Surebet calculator: split a stake so every result pays

What a surebet calculator is

A surebet calculator, also called an arbitrage calculator or arb calculator, is a tool that checks whether a set of odds from different bookmakers adds up to a profit on every outcome, and if it does, tells you the stake for each one. It works from one rule: divide 1 by each price, add the results, and if the total is under 100% the gap between that total and 100% is your profit.

Where the odds come from

Type in the best price you can find for each outcome, each from a different bookmaker. For a tennis match that is two prices, one per player. For a football match with a draw, three.

The prices usually come from one of two places. An arbitrage scanner lists them ready-made, with the bookmakers named. Or you find them yourself on an odds comparison grid and type them in. Either way, type what the bookmaker shows right now, not what the scanner showed a minute ago.

The calculator reads three formats without a switch: decimal (2.10), American with a sign (+110 or −110) and fractional (11/10). Mixing them in one calculation is fine.

Reading the result on the 2.10 / 2.05 example

Two tennis prices: 2.10 at one bookmaker on the first player, 2.05 at another on the second. Total stake 200.

1 ÷ 2.10 is 47.6%, the chance the first bookmaker is pricing in. 1 ÷ 2.05 is 48.8%. Together, 96.4%. That number is the one to watch. Under 100% means a surebet; over it means the bookmakers' margin wins whatever happens.

The big number, 3.73%, is the profit as a share of what you stake. It comes from 100 ÷ 96.4, which gives 1.0373. On 200 that is 7.47, and the calculator puts 98.80 on the first player and 101.20 on the second so that both sides return 207.47.

Under 100% combined is a surebet. The further under, the bigger the profit; a real one is usually between 0.5% and 5%.

Why the stakes are not equal

The bet with the lower odds needs the bigger stake, because it pays less per unit. The calculator sizes each stake in proportion to 1 ÷ odds, so the return is the same whichever side wins.

For two outcomes, the stake on the first is the total × (1 ÷ odds 1) ÷ (1 ÷ odds 1 + 1 ÷ odds 2), and the rest goes on the second. For three, the same rule with three terms. You never need to do this by hand, but it is why the split looks lopsided when one price is short.

Rounding, and why the profit becomes a range

Nobody bets 98.80. Bookmakers see stakes to the cent, and a stake of 98.80 next to a stake of 101.20 at another book is one of the clearest signs of arbitrage there is. The calculator rounds to whole units by default; the buttons switch to 5, 10 or no rounding.

Rounding breaks the equal return. With 99 and 101 the first side returns 207.90 and the second 207.05, so the profit is 7.90 if the first player wins and 7.05 if the second does. The calculator shows that range rather than an average, because the range is what you will actually get. On small stakes, rounding to 10 can eat the whole margin: check the range before you bet.

Round the stakes, then read the profit again. A 3% surebet rounded to tens can be a 1% one.

Fix one bet: when a bookmaker limits you

The second mode covers the most common thing that goes wrong. You place the first bet, the bookmaker accepts only 50 instead of the 98.80 you wanted, and now the other side has to match a smaller return.

Type the amount the bookmaker took straight into that Stake field. The calculator fixes it, lights the lock beside it, and sizes the remaining stake or stakes to match that bet's return; the total stake becomes an output instead of an input. Press the lock again to release it. This is also the mode for the reverse case: you have already placed one side and want to know what to put on the other.

Three-way surebets: 1, X and 2

Switch to three for any market with a draw (the rows become 1, X and 2), or for three-way handicaps and totals with a push line. The rule is the same: three prices, three implied chances, one combined total that needs to be under 100%.

Three-way surebets need three accounts at three bookmakers, and the combined total is harder to get under 100% because three margins are stacked against you. The example preset 3.40 / 3.60 / 3.50 gives 85.8% combined, which is a 16.6% surebet and a sign that one of those prices is a mistake. Real three-way arbs are small; big ones are usually a line that will be corrected or voided.

Exchange commission

Under “More options” is a field for the commission a betting exchange takes from winnings, usually 2% to 5%. It applies to the last outcome only, because that is where an exchange bet normally sits: back the favorite at a bookmaker, back the other side at the exchange.

Commission lowers the effective odds on that side, so a 2.05 at 5% commission counts as about 2.00. Leave it at 0 for two bookmakers. It is not a lay calculator: laying at an exchange, where you take the bet rather than place it, is a different sum.

Check the prices again before you bet

It cannot see whether the odds are still there. Prices move, and a surebet found a minute ago may be a loss by the time both bets are placed. It cannot know what stake the bookmaker will accept, or whether one side will be voided as a pricing mistake after the match starts, which leaves the other side at full risk.

What it can do is take the arithmetic out of the ninety seconds you have. Enter the prices, read the combined number, round the stakes, and then open both bookmakers and check the prices again before you confirm either bet.