CALCULATOR
Arbitrage betting calculator (surebet)
Free arbitrage betting calculator: enter the odds of each outcome and your bankroll to get the stake on each leg, the ROI and the profit; on half-point lines the profit is the same whatever the outcome. Legs can be sportsbook bets, Polymarket or Kalshi shares priced in cents, lay bets or a free bet. No sign-up; it all runs in your browser. For example, odds of 2.10 and 2.05 on a bankroll of 10,000 give a surebet with an ROI of 3.73% and a profit of 373.49.
On a bookmaker or lay leg, the field next to the odds is the commission on net winnings, % (as at Betfair); empty means none. On an exchange ¢ leg the fee is charged on top of the price: the venue rate is already filled in and can be changed.
Σ 1/k′ = 0.9640surebet
ROI 3.73 % · profit 373.49 whatever the outcome
| Leg | Odds | Stake | Payout | Threshold |
|---|---|---|---|---|
| 1 | 2.10 | 4,939.76 | 10,373.50 | 1.952 |
| 2 | 2.05 | 5,060.24 | 10,373.49 | 1.909 |
| Total staked | 10,000.00 | |||
The threshold is the value up to which the surebet holds: bookmaker odds no lower than it, an exchange price and lay odds no higher.
Settings
Real amounts are capped by bookmaker limits, and odds last only seconds. The rounding step is set in the settings: the calculator picks the best set of rounded stakes and works out the actual profit and ROI from the amounts shown.
How to use the calculator
- Choose a tab: "Surebet" for a new surebet, "Already placed" when one bet is in and you need to close the other leg or top up, "Handicaps and totals" for whole and quarter lines and middles.
- Set the number of outcomes, from 2 to 10, and the type of each leg: bookmaker, exchange ¢ (share price in cents and the venue: Polymarket with its market category, Polymarket US or Kalshi), lay or free bet. The calculator takes the exchange fee from the venue; for a bookmaker or lay leg, enter the commission on winnings if there is one.
- Enter the odds or prices: the best one for each outcome across venues. Decimals can be typed with a point or a comma; the odds format (decimal, fractional, American) is chosen in the settings.
- Choose what to calculate from: the bankroll, the stake on one leg or the limits. If a bet is already placed, use the "Already placed" tab: it needs the odds the bet was accepted at, not the current ones.
- Check the Σ 1/k′ line: below one means there is a surebet. Place the stakes from the table, starting with the leg at the book whose odds move more often or whose limit is lower; the leg threshold shows how far the odds can move before the surebet is gone. Copy the link to save the calculation.
How it is calculated
Each leg is reduced to net odds k′, the payout per unit spent: for a bookmaker k′ = k, with a commission c on winnings 1 + (k − 1) × (1 − c), for an exchange with price p and fee rate r 1 / (p × (1 + r × (1 − p))), and for a lay at odds L (L − c) / (L − 1), where the leg amount is the liability. There is a surebet when Σ 1/k′ < 1; the ROI equals 1 / Σ 1/k′ − 1 and the stake on leg i is bankroll × (1/k′ᵢ) / Σ 1/k′, so the payout is the same whatever the outcome. Two-outcome example: 1.85 and 2.25 → 0.541 + 0.444 = 0.985 < 1, ROI ≈ 1.5%. Three outcomes: 2.10, 3.60 and 4.20 → 0.476 + 0.278 + 0.238 = 0.992, ROI ≈ 0.8%. A free bet without stake returned pays amount × (k − 1), and the other legs cover that payout. A worked example is in the article “What Is a Surebet in Betting and How to Calculate It”; terms are in the glossary.
What the calculator does not account for
- Bookmaker limits: the maximum stake on a leg may be lower than the calculated one. The "Limits" mode works out the largest bankroll they allow.
- Time: according to Dozor data, the median surebet lives 2 seconds, and the odds may move before you place the second bet.
- Different settlement rules for the same market at two venues. On a cancellation, draw or postponement an exchange often resolves the market 50-50 and pays $0.50 per share, while a bookmaker refunds the stake; the "If 50-50" line shows that result.
- Currencies: if legs are in different currencies, the rate can move between the bet and the withdrawal, and buying and selling currency go at different rates. That is a separate risk of the surebet.
- Rounding: the step is set in the settings; the calculator picks the best set of rounded stakes and works out the actual profit and ROI from the amounts shown.
The calculator cannot find surebets. That is what the Dozor scanner does: it reads the lines of dozens of bookmakers and exchanges and shows pairs where Σ 1/k′ is already below one, with the stakes already split.
FAQ
What is a surebet in betting?
A surebet is a set of bets on every outcome of an event at different bookmakers that pays out more than the total stake whatever the outcome. It appears when bookmakers price the event differently or one of them is slow to update its line.
How is a two-outcome surebet calculated?
Add up the inverse odds: 1/K₁ + 1/K₂. If the sum is below 1, there is a surebet, and its return equals (1/sum − 1). Example: 1.85 and 2.25 → 0.541 + 0.444 = 0.985, return ≈ 1.5%. Stake on a leg = bankroll × (1/K) / sum.
How is a three-outcome surebet calculated?
Convert each odd into a probability (1/K) and add them up. If the sum is below 1, there is a surebet, and its return equals (1/sum − 1). Example: 2.10, 3.60, 4.20 → 0.476 + 0.278 + 0.238 = 0.992, return ≈ 0.8%.
How do I calculate a 4-way or larger surebet?
The same way as 2-way and 3-way: the sum of 1/k′ over all outcomes must be below one, and the stake on an outcome is bankroll × (1/k′) / sum. The calculator takes up to 10 outcomes: for example, 4 outcomes at 4.20 give a sum of 0.952 and an ROI of about 5%. The outcomes must cover every result of the event without overlapping.
What is a surebet leg?
A leg is one bet of the surebet on one outcome. The calculator sizes each leg so that the payout is the same whatever the outcome: stake = bankroll × (1/K) / sum of probabilities.
Is the surebet calculator free?
Yes. The calculator works without sign-up or payment, runs in your browser and does not send the odds you enter anywhere.
Why does the calculator not find surebets itself?
The calculator splits amounts across odds you already know. Finding surebets is the scanner’s job: it compares the lines of dozens of books and refreshes them to within 0.1 seconds.
How do I account for an exchange commission in a surebet?
Set the leg type to "Exchange ¢" and choose the venue: the calculator takes the price in cents and the venue fee, which is charged on top of the price, and turns the leg into net odds k′ = 1 / (p × (1 + r × (1 − p))). Example: Polymarket sports at 52¢ gives k′ = 1.878 instead of 1.923, so against a sportsbook at 2.20 the ROI is 1.31%, not 2.61%. For exchanges that charge commission on winnings, such as Betfair, enter the percentage in the leg commission field.
What if one bet is already placed?
Open the "Already placed" tab and enter the stake and the odds it was accepted at, plus the current odds of the other legs. Example: 5,000 accepted at 2.10, the other outcome now at 2.05: stake 5,121.95 and get 378.05 whatever the outcome. If you enter your book’s current 2.00 instead of 2.10, the calculator suggests 4,878.05 and the guaranteed profit turns out to be 121.95, 256 less.
How do I calculate a surebet with a free bet?
Set the leg type to "Free bet" and enter its amount: a free bet does not return the stake, so it pays amount × (k − 1), and the other legs cover that payout. Example: a 1,000 free bet at 5.00 against 1.25: 3,200 on the other leg, a profit of 800 whatever the outcome, a free bet conversion of 80%.
How are whole and quarter lines calculated?
In the "Handicaps and totals" tab. On a whole line (total 2), both bets are refunded at a total of 2 and the profit is 0. A quarter line of 2.25 is half the stake on 2 and half on 2.5, so equal payouts do not mean equal profits: over 2.25 at 2.10 and under 2.25 at 2.05 with stakes of 493.98 and 506.02 give 37.35, 18.67 and 37.35. The calculator sizes the stakes by the worst outcome: 488 and 512 give at least 24.80.
What is a middle and when does it pay off?
A middle is over on a low line and under on a high one, for example over 26.5 and under 27.5 rounds: at exactly 27 both win. At 1.95 and 1.95 with a 1,000 bankroll, 500 on each: outside the middle −25, inside +950. It pays off if the chance of landing in the middle is above 2.56%; the calculator shows that threshold.
How do I calculate a surebet across two currencies?
Turn on "Different currencies", choose the currency of each leg and enter the rate. Example: a sportsbook in euros at 2.10 and Polymarket in dollars at 47¢, a €1,000 bankroll and $1 = €0.92: €496.73 at the sportsbook, $547.03 on Polymarket (1,133.84 shares), ROI 4.31%. If you buy dollars at 0.93 and withdraw at 0.91, enter 0.93/0.91: the ROI drops to 3.17%.
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