Tennis value betting runs the same three steps as every other sport: turn each price into a chance, take the margin out, compare the fair price with what you can get. What is specific to tennis is where the money leaks. There is no draw, so the match winner market is two prices every operator takes seriously, which makes it one of the tighter books on the board and leaves little room for a price to be out of line.
The thin edge is only half of it. Tennis matches regularly stop before they finish, and operators do not write the same rule for what that does to your bet. An edge under one per cent can be smaller than the gap between two settlement rules, so in tennis the terms are part of the price rather than the fine print beside it.
The fair price when there is no draw
Two outcomes, so the arithmetic is short. A decimal price implies a chance of 1 divided by the price, so $2.00 implies 50%. Add both players: the amount over 100% is the overround, which is the operator's margin. Scale both chances down by the same factor until they add to 100% and you have a fair price for each player. Then edge = offered price / fair price - 1, and how to remove bookmaker margin works through the de-vig step on its own.
Worked example: a tennis head to head
Illustrative prices, chosen to show the arithmetic rather than a real match.
| Player | Priced at | Implies | Fair price |
|---|---|---|---|
| Favourite | $1.44 | 69.44% | $1.51 |
| Underdog | $2.85 | 35.09% | $2.98 |
The two implied chances add to 104.53%, so the overround is 4.53%. Scaling both down by that factor gives 66.43% and 33.57%, the fair prices in the last column ($1.50526 and $2.97917 before rounding). Now say the best price anywhere on the favourite is $1.48 and the best on the underdog is $3.00.
Example: the favourite at $1.48 against a fair $1.51 is an edge of minus 1.68%. The underdog at $3.00 against a fair $2.98 is plus 0.70%. One bet, one donation, and both were the top price on the board.
That 0.70% is a real edge. Hold onto the number, because the next section moves most of it without touching the price.
The settlement rule is part of the price
Three rule shapes are common, and they do not agree:
- Void unless the match is completed. A retirement refunds every single bet on the match.
- Stands once a set has been completed. The player who goes through is the winner, provided one set is in the book.
- Stands as soon as play has started. One serve is enough, and the player who advances wins the bet.
There is a public example of the first shape. Under the NSW Bookmaker Declared Betting Events Betting Rules, which bind bookmakers authorised in NSW, a match starts with the first serve and a single bet on one a player then fails to complete is void and refunded (clauses 5.2.8.1 and 5.2.8.3). Other operators write their own terms, so one retirement can be a refund at one and a settled bet at the next. Tennis retirement rules sets out the three shapes and what each one pays.
The same bet under two retirement rules
Take the plus 0.70% bet above, $100 on the underdog at $3.00, and add two illustrative assumptions so there is something to compute: 2% of matches end early, and 3 in 4 of those go to the favourite, as the player more often ahead when one stops. Neither is a measurement; both are inputs chosen to show the shape of the answer. That splits the 2% into 1.5% where the favourite advances and 0.5% where the underdog does, and the underdog's 33.57% fair chance of winning a completed match becomes 0.98 multiplied by 33.57%, which is 32.90% of all matches.
| Rule the bet settles under | Chance the bet is paid | Return on $100 | Edge |
|---|---|---|---|
| Void unless the match is completed | 32.90%, plus the $100 back 2% of the time | $100.69 | plus 0.69% |
| Stands as soon as play has started | 32.90% + 0.50% = 33.40% | $100.19 | plus 0.19% |
Same price, same opinion, same match. The rule alone took 0.50 of the 0.70 points.
The asymmetry runs the other way for the favourite. Price both at the fair $1.51 and $2.98: under a void rule each returns exactly $100.00, which is what fair means, while under the stands rule the favourite returns $100.26 and the underdog $99.49. The rule hands value to whichever player is more likely to be ahead when a match stops, which is usually the favourite.
Note: a walkover, where a player withdraws before a ball is struck, is normally void, because nothing has been triggered yet. The divergence starts at the first serve.
So four things in the terms decide whether your number survives: the retirement trigger, whether a disqualification counts as one, how a suspended match is treated if it resumes and if it never does, and how a handicap or total settles when the score had not decided it. An edge computed on one rule and settled under another was never an edge, which is also why two operators on different rules are a trap on one match: see arbitrage rule mismatches.
Sizing a 0.70% edge
The Kelly stake is edge divided by the price minus one, as a share of bankroll: 0.70% divided by 2.00 is 0.35%, and a quarter Kelly on a $2,000 bankroll is about $1.75. The expected value of that bet is 0.70% of $1.75, a little over one cent. That is the honest end of the arithmetic, because the edge is real and it can still be too small to be worth the click.
Two other numbers put it in proportion. One step down the price, $3.00 to $2.95, turns plus 0.70% into minus 0.98%: a swing of 1.68 points, more than twice the edge you found. The settlement rule above is worth another 0.50, which is most of what the edge was. Neither of those is a market opinion, and both move the number by more than the opinion did.
Risk: Betting involves risk. Bookmakers can restrict or close accounts and void bets, automation can fail, prices move, and a positive expected value bet can still lose. There is no guarantee of profit. See responsible gambling for limits and support. A bet above the fair price loses regularly, and at these edges a long losing run is ordinary rather than evidence of anything. The fair price is an estimate, and there is no guarantee of profit.
Where the margin sits across tennis markets
Measure it per match with the book total. Illustrative prices again, with the hold worked as 1 minus 1 divided by the book total, which is the share of turnover a market keeps when stakes go on in proportion.
| Market, illustrative prices | Book total | Overround | Hold |
|---|---|---|---|
| Match winner, $1.44 and $2.85 | 104.53% | 4.53% | 4.34% |
| Game handicap, $1.87 and $1.95 | 104.76% | 4.76% | 4.54% |
| Total games, $1.85 and $1.95 | 105.34% | 5.34% | 5.07% |
| Set betting best of three, $2.10, $4.00, $4.50 and $6.50 | 110.23% | 10.23% | 9.28% |
The set betting row keeps 9.28% against the match winner's 4.34%, a little over twice as much, for the same opinion expressed in a market with four outcomes instead of two. Tennis handicap betting and tennis total games betting work through how those two settle.
What moves the price, and what to check
Withdrawals and surface do most of the moving. A player pulling out voids singles on their own match, but it also reshapes the draw, so a fair price on a tournament outright built before the news is pricing a draw that no longer exists. The same two players are a different matchup on clay, grass and hard court, and best of five gives the better player more chances to express the gap: tennis betting explained has the set-to-match arithmetic.
Then the checklist, roughly in the order these go wrong.
- The settlement rule, as above, because it took most of the edge in the worked example.
- The price's age. Prices are read on a repeating cycle rather than tick by tick, so confirm the price in your account before you bet.
- The same handicap or total on both sides. Minus 3.5 games and minus 4.5 games are different propositions, so comparing the two manufactures an edge out of a difference in the bet.
- The same match. Qualifying draws, doubles and exhibition events carry similar names, and a screen keyed on player names can line up two of them as one row.
- The clock. Online, an Australian provider may only take the bet before the match starts, so every number here is a pre-match one (in-play betting in Australia).
- The sample. At under one per cent, profit takes a long time to say anything, while closing line value answers sooner.
Where B337 fits
The +EV screener lists bookmaker prices that sit above a fair price and ranks them by edge, with the fair price built by taking the margin out of prices across the market and combining them. The de-vig is adjustable, so you can change which prices count and how much margin comes off each, and every edge is worked out again to match. Filter by sport, market and bookmaker.
Two honest limits. The fair price is an estimate rather than a known probability, so a price above it can still lose. And B337 places no tennis bet by itself: the screener finds the price, and you place it into your own bookmaker accounts by hand, from the Terminal on Terminal Pro or Full Automation. A free account shows the live count of prices above fair and the best edge on the board, with the rows locked.
Nothing in a screener reads an operator's retirement rule, so that check stays yours. For the same arithmetic on a three-outcome sport see soccer value betting.