How to Calculate a Surebet: Formula, Stakes and Mistakes
How to check a surebet, split stakes across two and three legs, round amounts, handle limits, and why an ROI above 10% is a red flag. Examples and a calculator.
A surebet is calculated in three steps: add up the inverse odds, confirm the sum is below one, and split the bankroll in proportion to the inverse odds. Everything else in this article is about where the math parts ways with reality: limits, rounding, three outcomes, fees. You don't have to do it by hand — there's a calculator — but you do need to understand what it does.
Step 1. The check
For outcomes with odds k₁, k₂ (and k₃ for three outcomes):
Σ = 1/k₁ + 1/k₂ (+ 1/k₃)
If Σ < 1, there's a surebet. ROI equals 1/Σ − 1.
| k₁ | k₂ | Σ | Surebet | ROI |
|---|---|---|---|---|
| 2.10 | 2.05 | 0.964 | yes | 3.7% |
| 1.95 | 2.00 | 1.013 | no | −1.3% |
| 3.40 | 1.45 | 0.984 | yes | 1.6% |
| 1.30 | 4.60 | 0.987 | yes | 1.3% |
Step 2. Splitting the bankroll
The stake on leg i equals bankroll × (1/kᵢ) / Σ. That way the payout on every leg is the same.
Bankroll of 10,000 ₽, odds of 2.10 and 2.05, Σ = 0.964:
| Leg | Calculation | Stake | Payout |
|---|---|---|---|
| 1 | 10,000 × 0.476 / 0.964 | 4,940 ₽ | 10,374 ₽ |
| 2 | 10,000 × 0.488 / 0.964 | 5,060 ₽ | 10,373 ₽ |
A profit of 373 ₽ whatever the outcome — the same 3.7%.
Three outcomes
Win, draw and loss, or three teams in a group market. The formula is the same with three terms, and so is the split. Three legs at three bookmakers have to be placed before any of the three odds changes, so three-way surebets in live almost never work out in time, and in prematch they require three accounts with sufficient limits.
Where the math parts ways with reality
- A limit on one leg. The bookmaker accepts 3,000 ₽ instead of 4,940 ₽. Then you recalculate from the limit: the second leg equals 3,000 × (1/2.05) / (1/2.10) = 3,073 ₽, and total profit shrinks proportionally. The calculator works from the bankroll; you only find out the limit at the bookmaker.
- Rounding. Stakes of 4,940 and 5,060 ₽ look calculated, and that gets noticed. Rounding to the nearest hundred (4,900 and 5,100) shifts payouts by tens of rubles and makes the split uneven: a profit of 290 ₽ on one outcome and 455 ₽ on the other. That's the price of staying inconspicuous, and it's small.
- The odds moved. Three seconds passed between the first and second bet, and the second price dropped from 2.05 to 1.95. Σ became 0.989, and ROI 1.1% instead of 3.7%. At 1.90 there's no surebet left. According to Dozor data, the median surebet lifetime is 2.1 seconds, so you need to bet with the stakes already worked out, not calculate after the first bet.
- Different settlement rules. One book settles total rounds on a map including overtime, another without it. The math is right, but there's no surebet.
- Fees and currency. On prediction markets the platform fee is deducted from the payout, and the dollar-to-ruble exchange rate feeds into ROI. More in the article on arbitrage with Polymarket and Kalshi.
Why a high ROI is a red flag
According to Dozor scanner data for the 24 hours of September 6, 2026, the median ROI of the surebets found was 3%, and nine out of ten were below 9%. A 15% surebet in live almost always means one book hasn't updated its line after something happened in the match, or has mispriced the line. A bookmaker is entitled to settle a bet at erroneous odds at odds of 1, and then the second leg remains an ordinary bet with ordinary risk. The rule is simple: the higher the ROI, the more carefully you check the rules and the price age.
What it means in money
At a 3% ROI and a 10,000 ₽ bankroll, a surebet earns 300 ₽. Twenty surebets a day is 6,000 ₽ on 200,000 ₽ of turnover. The realistic figure is lower: limits, limited accounts, moved odds and voided bets eat into it. Surebets are low-margin, high-turnover work, not a one-off win.
FAQ
Do I have to bet the exact calculated stakes?
No. Rounding to the nearest hundred changes the profit by tens of rubles and makes your bets less conspicuous.
How do I calculate if the limit is below the calculated stake?
Work from the limit: the stake on the second leg equals limit × (1/k₂) / (1/k₁).
What if the second leg doesn't go through?
You're left with an ordinary bet. Your options: hedge it with an opposite bet at a third book at the current line (usually at a small loss), or leave it as it is.
How is ROI different from margin?
Margin is a single book's markup over fair probabilities. A surebet's ROI is the negative combined margin of two books against each other. The terms are in the glossary.