Guide to Betting on Tennis
Tennis is a sport played around the world, and it's becoming increasingly popular with fans looking to get into betting.
Tennis ranks behind only soccer (football) and horse racing in terms of money generated for bookmakers in the United Kingdom, and there is good reason that more and more people want a piece of the action: it's an intriguing game that offers a wide array of markets, and tournaments take place throughout the year.
Are you missing out and want to learn more?
A Beginner's Guide to Tennis
Before we jump into how a game of tennis is played, let's start with the very basics: where tennis is played. Tennis takes place on a rectangular court that is divided into two halves by a net across the middle. Each half of the court as two sides, the deuce side (the right) and the ad side (the left). On each side of the court there is a service box which runs from the net until just over half way to the edge of the court (the baseline). When serving, a player will look to hit the ball into their opponent's service box diagonally across from where they are serving from. There are alleys running the length of the court which are out in a singles match, but are in play in a game of doubles.
Now that we've got a lay of the land let's get to grips with the scoring system - and be warned, it's a little strange! Each player begins the game with '0' except this isn't your regular zero. In tennis, when a player has '0' it's called 'love'. Winning one point will take you to 15, a second point to 30, a third to 40, and if a player wins a fourth point then they will win the game - unless the players were at 'deuce' that is. 'Deuce' is the term used when the score is 40-40. From there, the winner of the next point will go to 'advantage'. If that same player wins the next point they will also win the game, but if they lose the point, the score returns to deuce.
A game forms part of a 'set' which is played to six or seven, with a player needing to win by two games. So, if a player is 6-5 up, they have the chance to win 7-5. If both players reach six games each then the set moves to a tiebreaker which you can think of as an additional game that's played to seven points. A tennis match consists of either three or five sets depending on the competition.
Ready for the action now? To get a tennis match underway, the players (or teams) stand on opposite sides of the net. One player will serve the ball to the other, aiming to land the ball into the service box diagonally across from where they're serving from. The player serving (known as the 'server') will start from the right side of the court and has two opportunities to get the ball into play. If they fail to get it in play on their first go then that's a 'fault'. If they can't get the ball in play with their second serve too then it's a 'double fault' and they lose the point.
For now assume that you're dealing with a great server who hits the ball into the correct serve box at the first attempt. From there the players hit the ball back and forth until one player hits a 'winner' (the ball bounces in the court and their opponent can't return it) or one player commits an 'error' (the ball is hit into the net or outside of the court). The winner of the point gets 15 and the loser gets 0, taking the score to 15-0 or 'fifteen-love'. From there the players slog it out to win the game, the set, and eventually the match.
The Fundamental Rules
It's time to delve a little deeper into some of the essential rules of tennis:
Tennis' scoring system may seem a bit confusing (or fairly arbitrary) at first, but we've once you get the hang of it things are pretty straightforward.
As we've already briefly been over, every game begins with the players on zero or 'love'. From there the scoring goes like this:
- Winning one point will take you to 15
- A second point to 30
- A third point to 40
- A fourth point could win you the game
However, that's where 'deuce' comes in. If the scores are level at 40-40 then the score then one of the players need to win two consecutive points to win the game. If a player wins one more point then the score moves to 'advantage'. If they then lose the next point the score returns to deuce. That process can go on indefinitely, but it's usually not too long before the game is resolved.
Once again there is a catch though: if a player is 6-5 ahead, they have the opportunity to win that game and take the set 7-5. However, if they don't win the game and the scores are then tied, the set moves to a tiebreak.
A tiebreak is a race to seven points, but like in the set itself, a player needs to win by two points. The scoring system in a tiebreaker is different to that of a normal game, with the score simply going 0, 1, 2, 3 etc. The order in which the players serve is also different. The player who received serve in the preceding game serves first in the tiebreaker. They serve the first point of the tiebreak, after which their opponent serves twice. From there, the players rotate serving, with each player serving twice per turn. When six points have been played and then for each multiple of six after that, the players switch sides.
Matches are played over three or five sets. In women's tennis, a best-of-three format is always used, while in men's tennis the same format is used for many ATP Tour events, but in grand slams, men play best-of-five set matches.
The serve is an all important weapon in a tennis player's arsenal, and it's also fundamental to learning about the game as the serve is where play begins.
A few key rules to remember about serving:
- A pre-match coin toss determines which player serves first.
- Players alternate which side of the court they serve from, with the right side (the 'deuce side') always served from first
- The server will aim to hit the ball into the service box diagonally across from them.
- At no stage can the server's feat move in front of the baseline before the serve. Should they do so, a foot-fault is called.
- If the server misses with their first serve (it goes into the net or outside the court), they have served a fault.
- If a fault is served, a player can make use of their second serve. If another fault is served then it is a double fault and the server loses the point.
- If a serve clips the top of the net it is called a 'let'. If the serve hit the net and went into the service box then they don't lose a serve. However, if the serve clips the net and goes outside of the service box it is a fault.
- There receiver does not have to stand in a particular position, but it is standard for them to take up a position on or just outside the baseline diagonally across from the server.
- Once a serve is in play, a rally ensues and play is only ended when one player hits the ball into the net or outside of the court.
Once a point is underway there are a few basic regulations:
- A player cannot hit the ball twice
- A player must hit the ball before it bounces for a second time
- The ball must be hit within the boundaries of the court to remain in play
- If the ball hits the line or any part of the line, it is in
- If a player touches the net either with their body or their racket, they lose the point
- If the ball is hit into the net, the point is ended
Easy, isn't it?
There are two types of officials who enforce the rules during a match, line umpires and the chair umpire.
Line umpires work in teams of up to nine officials, and are responsible for calling whether or not a ball is in play. They, as the name suggests, are stationed to view specific lines of play.
The chair umpire oversees the game from an elevated chair that is in line with the net. The chair umpire has the final say on all calls, and can overrule the decision of the line umpires. The chair umpire is responsible for keeping score, and calls out the score to the players at the end of each point. Additionally, the chair umpire is also charged with ensuring players obey the rules of the game and can hand out penalties (known as 'code violations') if the rules are infringed upon.
There are two additional off-court officials, the tournament referee is charged with ensuring that the tournament as a whole is played to the rules of tennis, and a chief umpire who appoints chair umpires to matches and is in charge of the administrative side of umpiring.
The A-Z of Tennis
One of the most important and also most confusing parts of learning a new sport is the terminology associated. Sometimes it can sound like the sportscasters and your friends are speaking another language of sorts. To help you out with this, we have put together a full glossary of tennis related terms for you to review or reference when needed.
How Tennis is Run
The International Tennis Federation (ITF) is the governing body of all things tennis, including beach tennis which we bet you didn't even know was a sport (we didn't either).
The ITF is affiliated with 211 national tennis associations and six regional associations, and is charged with the administration and regulation of the sport, organizing international competitions, and developing and promoting the sport.
The ITF partners with the Association of Tennis Professionals (ATP) and the Women's Tennis Association (WTA) to govern professional tennis. The ITF remains responsible for organizing grand slams, the Fed Cup, the Davis Cup, tennis at the Olympics and the Futures-level tournaments.
Originally created in the 1970s to protect the rights of professional men's tennis players, since 1990 the Association of Tennis Professionals (ATP) has organized the premier men's tennis tour, the ATP World Tour. In addition, the ATP manages the Seniors Tour.
The ATP World Tour comprises of: the ATP World Tour Masters 1000, ATP World Tour 500 Series, and ATP World Tour 250 tournaments.
The ATP also oversees the ATP World Rankings, the merit-based system which determines the rankings of players. The ATP Rankings are in place for both singles and doubles, and are used for determining qualification for all tournaments and the seedings used in them.
The seven-member ATP Board of Directors governs the ATP together with a 12-man Player Council, and a Tournament Council made up of 13 representatives from across the globe.
Like the ATP, the Women's Tennis Association (WTA) has its origins in the 1970s, and evolved into the primary organizer of women's professional tennis.
The WTA comprises of: Premier Tournaments, International Tournaments, and the WTA 125k Series.
The WTA has its own ranking system, it too is a merit-based, rolling 52-week, cumulative system that ranks both singles and doubles players. It is used to determine who qualifies for an event, and how players are ranked at tournaments.
The WTA is governed by a board of directors, with an eight-member Players' Council set up as a sub-committee to advocate the opinions of the players.
A Brief History of Tennis
What do European monks, French Kings, and King Henry XIII have in common? We'll forgive you for not guessing that they were all tennis pioneers! Yes, tennis is believed to have its roots in 12th century Europe when monks in Italy and France struck balls with the bare hands in a game known as jeu de paume or 'game of the hand'.
As the sport developed into 'real tennis' it soon became popular with the aristocracy and first King Louis X of France and later King Charles V of France took a liking to the game which by this stage was played with paddles, the precursor to rackets. Across the Channel in England, King Henry VIII was not to be outdone, and had a court built at the Royal Palace of Hampton Court - one which still exists today.
It was in England - many years after the King had met his demise - that 'lawn tennis' rose to prominence and the foundations of modern tennis were laid. It's Major Charles Wingfield who is credited as the founder of the modern game, and in 1874 Wingfield patented the equipment and rules for the game of tennis.
The All England Croquet and Lawn Tennis Club made a few tweaks to Wingfield's game that included changing the court to a rectangle, and allowing for over-arm serving. Remarkably, just three years after Wingfield patented the game the first edition of Wimbledon was held.
Tennis continued to be refined in the years that followed, but by the 1890s tennis had reached a stage of development that produced a game not too dissimilar from what we know tennis as today. In fact, tennis' rules and scoring system have changed little in the last 120 years, with the addition of the tiebreak in the 1970s one of the few major changes.
The crown jewels of the sport, the grand slams, originated during this period of development, with the US Open hosted for the first time in 1881 - four years after the maiden edition of Wimbledon - with the French Open (1891), and Australian Open (1905) following not too long after.
It was in the 1920s that players began to play tennis professionally, but it was not until 1968, the dawn of the Open Era, that professionals were able to play in all events. Before that point, only amateurs were able to play in the grand slams. The Open Era saw a professional circuit develop, and the Association of Tennis Players (ATP) and the Women's Tennis Association (WTA) were formed to look after the interests of the players.
There has been no looking back from that point with tennis now a global sport that has seen the rise of worldwide superstars the likes of Roger Federer and Serena Williams. Revenue from television rights and advertising means that tennis' top players are among the richest in the world; Federer walked away with $2,882,660 for winning the 2017 men's singles title at Wimbledon, a far cry from the $18 awarded to Spencer Gore for winning the inaugural edition of the Championship.
Betting on tennis comes down to picking winners and losers. One of the best ways to start learning how to pick winners and losers is to study some of the legends of the sport. You can see how their styles worked and didn't work and use that to your advantage moving forward. Also, knowing these people will help you to fit in when discussions happen at the bar or around the courts. If you don't know the most famous tennis players of all time, people will be confused and look at you funny.
Tennis' Big Events
Tennis has four grand slam events: the Australian Open, the French Open, Wimbledon, and the US Open. These are the most prestigious tournaments on the calendar, and offer the most prize money, ranking points, and, of course, fame.
Contested over two weeks, grand slams have five categories - men's singles, women's singles, men's doubles, women's doubles, and mixed doubles. Players can participate in multiple categories, and many do so with much success. In addition, there are junior's championships and wheelchair championships.Australian Open
The Australian Open, the opening grand slam of the year, is played on the hard courts of Melbourne Park in Melbourne, Australia from mid-January.
The first Australian Open was first held in 1905, and, in a lesser-known piece of trivia gold, was originally held on grass. The tournament was not designated a grand slam until 1924, and was held in five Australian cities and two New Zealand cities (so much for the 'Australian' Open...) before it settled in Melbourne in 1972.
The Melbourne Park complex has played host to the tournament since 1988, and the venue has boasted a number of firsts. It was at the Australian Open that retractable roofs were first used in the case of rain or extreme heat. The show courts - the Rod Laver Arena, Margaret Court Arena and the Hisense Arena -are all equipped with retractable roofs. Blazing-hot temperatures can make the Australian Open even more of a challenge, with the event forced to adopt an 'extreme heat policy' after criticism that players were forced to play in dangerously hot temperatures; In 2014, when temperatures reached 111.0 °F, a number of players collapsed (one even began to hallucinate), while others said their shoes and water bottles were melting!
Despite the penchant for hot conditions, the Australian Open has set the bar for crowd attendance. In 2017, the Australian Open was attended by 728,763 people, bettering the previous record at a grand slam which was held by the 2009 US Open which was attended by 721,059 people.
Prize money isn't in short supply at the Australian Open either.
Not bad for two week's work!
Williams is the most successful women's singles player at the Australian Open in the Open Era, bagging the Daphne Akhurst Memorial Cup seven times. Novak Djokovic leads the way in the men's singles race, with the Serbian having taken home the Norman Brookes Challenge Cup on six occasions.French Open
In May and early June of each year, the tennis roadshow heads to Paris, France for the Championnats Internationaux de France de tennis, known to us commoners as the 'French Open' or simply 'Roland Garros'.
The French Open is held on the clay courts of the Stade Roland-Garros (hence the nickname), a surface which makes it a unique challenge - one that has been too great for some of the game's greatest players. On grass and hard courts it's a big serve and booming groundstrokes that are a recipe for success, while on clay players are forced to contend with a surface that is slower and produces a higher bounce, resulting in longer rallies and play from behind the baseline.
Founded in 1981, the French Open has been played at Roland Garros since as early as 1928, lending the event an extra layer of historical charm. The Roland Garros complex comprises of 20 courts, including three stadium courts: Court Philippe Chatrier, Court Suzanne Lenglen, and Court 1.
The tournament holds the honor of being the first grand slam to include amateurs and professionals, embracing the term 'open' in 1968. The French Open offers less prize money than the other three majors on the calendar, but with €2,100,000 up for grabs for the winner of the men's and women's singles, it's still a bounty that shouldn't be scoffed at!
Rafael Nadal is the undisputed 'King of Clay', and the Spaniard claimed a record 10th title at Roland Garros in 2017 - forget a trophy cabinet, Nadal will need a whole room to fit all 10 of his Coupe des Mousquetaires! In the women's singles, there were records of a different nature being set in 2017, with 20-year-old Jelena Ostapenko claiming the coveted Coupe Suzanne Lenglen, a trophy that was not only here first grand slam title, but also her first at full Tour level!Wimbledon
Wimbledon is considered the pinnacle of tennis by many fans and players; as the oldest tennis tournament in the world, it's layered with history and tradition that sets it apart from the rest.
First held in 1877 at the All England Lawn Tennis and Croquet Club in London, England, Wimbledon or 'The Championships, Wimbledon' as the event is officially called, is the only grand slam still played on grass. The tournament gets underway on the first Monday in July, and depending on the unpredictable British weather can either be plagued by rain or searing heat more commonly associated with the Australian Open! The All England Club comprises of 19 courts, with the two show courts, Centre Court and Court One, only used for Wimbledon.
Wimbledon involves a number of traditions which make it both unmistakably English and a unique event. The tournament has historically been closely linked with British royalty, and until 2003 players bowed or curtsied to members of the royal family seated in the Royal Box when they entered or left Centre Court. Yes, in the 21st century tennis players were still bowing and curtsying! Staying on the theme of being prim and proper, at Wimbledon there is no men's or women's events, but rather the competitions are referred to as the 'Gentlemen's' and 'Ladies'' events.
Purple and green might be the official colors of Wimbledon, but don't expect to see much color on the players, with strict uniform rules asserting that players can only wear white, with the outfitter's logo the exception. It's not just the players at Wimbledon who may look a little different, but also the courts: there is no advertising on or around the Wimbledon courts. Despite this lack of advertising, Wimbledon still holds the longest running sponsorship in sports history, having made use of Slazenger since 1902.
It was at Wimbledon where ball boys and ball girls first came to the fore. For many years the ball kids were selected from a local orphanage, but in more recent years it's the local schools where children are chosen from. As you would expect, ball kids are dressed in purple and green, and their behavior is impeccable!
All this may appear a little bit over the top, but whether you're a fan at the All England Club sitting on the hill watching the action while eating strawberries and cream or enjoying the tennis from the comfort of your sofa, there is something very special about Wimbledon.
The ladies champion is presented with the Venus Rosewater Dish, and the gentleman's winner takes home the Gentlemen's Singles Trophy which comes with the an inscription befitting the tournament: "All England Lawn Tennis Club Single Handed Championship of the World"!
The legendary Roger Federer racked up his eighth Wimbledon title in 2017, a new record for men's singles titles won. However, the Swiss maestro is still one behind Martina Navratilova who has nine women's singles titles to her name.US Open
The US Open takes place on the hard courts of the USTA Billie Jean King National Tennis Center in Flushing Meadows, New York. The tournament kicks off on the last Monday of August so that the middle weekend of the event coincides with the Labor Day weekend.
The US Open has its roots in the U.S. National Championship which first took place in 1881 in Newport, Rhode Island, making it one of tennis' oldest tournaments. The tournament moved to the USTA National Tennis Center in Flushing Meadows, Queens in 1978 and it was then that it made a permanent switch to hard courts, having first been played on grass and then clay.
While the Australian Open is also played on a hard court, the surfaces at the two venues does differ slightly, with the Pro DecoTurf surface on offer at Flushing Meadows producing less bounce than other hard courts. The courts also look slightly different - while the Australian Open courts are entirely blue, there area around the courts at the US Open are green to help viewers distinguish the playing surface.
The USTA Billie Jean King National Tennis Center boasts 22 courts - four show courts (Arthur Ashe Stadium, Louis Armstrong Stadium, Grandstand and Court 17, also known as 'The Pit'), 13 field courts, and five practice courts. The 22,547-seater Arthur Ashe Stadium is the world's largest tennis venue.
The winner of the men's and women's singles each secure a massive $3.5 million.
In 2006, the US Open delivered a first in grand slam tennis when it introduced instant replay reviews of umpire and line judge calls, with a system known as 'Hawk-Eye'. The system is now used at all grand slams and most major tournaments.
The US Open differs from other grand slams in that there are tiebreakers in every set - at other grand slams there is no tiebreaker in the final set (the third set for women, and the fifth set for men).
Jimmy Connors, Pete Sampras, and Roger Federer share the honor of having won the most men's singles titles at the US Open (five). Chris Evert and Serena Williams top the charts among the women's singles winners with six titles each.
The grand slams are undoubtedly the crown jewels of tennis, but there are plenty of other prizes to play for. Most notably the end-of-season Tour Finals. The regular season on the ATP and WTA Tours is structured in a similar fashion, but there are a few differences.Men's Tennis
The main ATP Tour has three levels: Masters 1000, 500 series, and 250 series.
The Masters Series consists of the year's nine Masters 1000 events (named as such for the number of ranking points on offer), and culminates with the ATP Tour Finals which features the top-eight ranked players. Four of the Masters 1000 tournaments - Indian Wells, Miami, Madrid, and Beijing - are held concurrently with the WTA, creating a crackerjack 10 days of tennis that at times can feel a bit like a grand slam.
The eleven ATP Tour 500 series tournaments still have a lot to offer when it comes to prize money - the winner of the Dubai Tennis Championships takes home nearly two million dollars - and with 500 ranking points on offer they are still important events.
The 250 series tournaments are a little lower key as players fight it out for ranking points to get to the bigger events.
A level below that is the Challenger Tour which players ranked lower than 80 take part in. This is the lowest level run by the ATP, and prize money ranges from US$25,000 and US$150,000.
The Futures Tour, which is administered by the ITF Men's Circuit, is the lowest level of professional tennis. Players can still win US$10,000 and US$15,000, and there are some pretty interesting tournament venues like Sri Lanka and Zimbabwe!Women's Tennis
Over on the women's circuit, it's the 'Premier' events which are the most prestigious. There are three levels of 'Premier' events: Premier Mandatory, Premier 5, and Premier.
'Premier Mandatory' might not sound like a tournament you want to play in, but these are the events held together with the ATP Tour and that provide the most ranking points and prize money. No surprises here in that there are five 'Premier 5' events, while there are 12 'Premier' tournaments.
Like on the ATP Tour, the WTA Tour ends with a huge finale, the WTA Championships which sees the eight top-ranked singles players, and the eight top-ranked doubles players doing battle.
The second-tier of tour competition in women's tennis is the International Tour which consists of 32 events joined by the WTA 125k Series.
There is some international flavor to the tennis schedule, with international team events the Davis Cup and Fed Cup held on an annual basis. The Davis Cup sees the stars of the men's game battle it out for their countries, while the women face off in the Fed Cup. The two competitions can be thought of as being a bit like the World Cup of tennis.
Qualification for the two events differ slightly, but the end result is the same, with top 16 teams slug it out through four rounds of ties for the right to feature in the final. Each tie is played in a best-of-five format over two days in the Fed Cup and three days in the Davis Cup.
In the Fed Cup, on the first day two singles matches (known as 'rubbers') are played, with the reverse singles matches played on the second day. The doubles rubber rounds out the second day and the tie. In the Davis Cup, the first singles matches are played on day one, the doubles match takes place on day two, and the reverse singles takes place on the third and final day.Olympic Tennis
Tennis first appeared at the Summer Olympics in 1896, but it wasn't until 1988 that it became a permanent feature at the Games.
There are five events at the Olympics: men's singles, men's doubles, women's singles, women's doubles, and mixed doubles. The surface on which the event is played varies according to which nation is hosting the Games, but has predominantly been played on hard courts.
Venus Williams tops the medal-winning charts at the Olympics, having claimed four gold medals and one silver medal. The Olympics form part of the 'Golden Slam', an achievement which entails winning singles gold at the Olympics as well as all four grand slams in the same year. Steffi Graf is the only player to have achieved the Golden Slam, sweeping the big events in 1988.
How to Bet on Tennis
Tennis odds are available on just about any tennis match you could imagine, ranging from the grand slams to the lowest-tier, the Futures Tour, and that's a major plus to betting on tennis: if you want to bet on a match you'll be able to find a bookmaker who will enable you to do so.
Looking at some tennis betting basics, there are five main types of betting: outright betting, match betting, handicap betting, over under betting, and in-play betting.
In an outright bet, you'll be picking the winner of a tournament, not just a single a match. Depending on the tournament, this could require as many as seven individual match victories.
As the name suggests, match betting relates to a single match - you pick the winner or the loser. This is the most straightforward method of betting on tennis.
If you're familiar with betting on American sports then you probably do a lot of spread betting, tennis handicap betting is the tennis equivalent.
There are two areas of handicap betting, set handicaps and game handicaps, both of which are fairly straightforward. One player is given a number of sets or games as a handicap to level the playing field. You then decide whether Player A will win with a handicap advantage or whether Player B will make up their handicap disadvantage and still win. For example, if Roger Federer has a games handicap of -8 to beat John Isner who has a handicap of +8, and Federer wins 6-4, 7-6, 6-3 the games score is 19-13 in Federer's favor. So, while Federer has won the match, you would lose your bet if you put money on the Swiss to overcome his handicap.
Set handicaps work in the same fashion, except the handicap is a number of sets rather than games.
As is the case with handicap betting, with over under betting you're looking at either the number of games or sets that will be played. This is again a two-way bet where you put money on the number of games or sets being more or less than the number offered.
For this example, let's use sets rather than games. In a WTA Tour contest, the match will be a best-of-three set affair, so you will be offered odds on under 2.5 sets or over 2.5 sets. Let's say Serena Williams is up against Angelique Kerber, and you're confident the American is going to win in straight sets then you would bet on under 2.5. In other words, you think that all three sets will not be required.
In-play betting is emerging as a popular go-to spot for tennis punters. Tennis moves relatively quickly - a game can be over in a matter of minutes, and matches can finish in less than an hour - so you need to be on your toes, but there are plenty of opportunities to bet on individual games and sets.
If you don't want to wait it out to the end of a tournament, there are many options to explore. For instance, you can bet on a player to reach a certain point of the tournament or pick the winner of one half of the draw.
A match bet can be made more intricate by picking the number of sets you expect the match to last and how many sets each player will win. This is known as set betting.
Betting on the margin of victory can be an interesting category. A three-set match provides six different possible outcomes.
Set winner is also a good one to keep an eye on. Backing an underdog to be quick out of the blocks and win the first set but lose the match can have good value.
Some bookmakers will offer a 'double result' category which allows you to bet on two different events in the match. For instance, you might bet on Andy Murray to lose the first set and win the match, coupling two bets together.
Tennis Betting Strategy
When betting on tennis there is one thing to always remember: look for the value. Over the long-term you'll come out on top by being patient and consistently making smart bets where the value is evident rather than backing a host of long shots in the hope of a big payday.
This principle can make betting on tennis tricky because the value can at times be hard to spot as it's a sport in which the favorites get the job done significantly more often than upsets occur. But value doesn't mean longer odds and bigger returns, it means spotting the opportunities where your research shows that the odds on offer play in your favor.
If you want to apply a strict principle to finding value, a useful formula is: Value = (Probability * Decimal Odds) - 1. To find the 'probability' value for that formula there is no substitute for good, old research.
As with any sport, there are a number of factors that influence the outcome of each bet, and a bit of pre-bet research will go a long way.
There are three surfaces on which tennis is played: hard-court, clay-court, and grass, and each is a very different prospect. Every player has their preferred surface, and it tends to go beyond player preference: a champion on grass might be cannon fodder on clay.
With that in mind, the first thing to look at when considering a bet is how a player fares on that surface. If history suggests a player is weak on grass then don't count on them to buck the trend any time soon, it's likely that the surface simply does not suit their style of play.
Much like favored surfaces, players have opponents who they consistently struggle against. Roger Federer holds the lion's share of win-related records in men's tennis, but the Swiss has a 14-23 head-to-head record against arch-rival Rafael Nadal.
There is nothing special about tennis on this one; if a player is struggling today they're likely to be struggling tomorrow, upturns in fortune are generally seen over the course of a few tournaments.
There is a mass of free, readily available data on tennis players, make sure you tap into it. From the average speed of a player's serve to the break points they've saved to the number of trophies in their cabinet, it's all available and it should make a difference on who you bet on and why.