Sure Bet Calculator: How the 2-Way and 3-Way Formulas Work
Every sure bet calculator is doing the same handful of steps behind the scenes. Here's exactly what those steps are, so you can sanity-check any number it gives you.
How does a sure bet calculator work?
A sure bet calculator divides your total stake across every outcome of a market so that the payout is identical no matter which outcome wins. It does this by weighting each stake in proportion to the inverse of its odds, so the outcome with the shortest odds gets the largest stake and the outcome with the longest odds gets the smallest.
What a Surebet Calculator Actually Calculates
At its core, a surebet calculator is solving one problem: given a set of odds from different bookmakers for every outcome of the same event, how do you split a total stake so that your payout is the same regardless of which outcome happens? It does this using the implied probability of each price, which is simply 1 divided by the decimal odds.
Add up the implied probabilities across all outcomes and you get the market's total 'book percentage.' If that number is below 100%, an arbitrage exists, and the gap below 100% is roughly your guaranteed margin before stakes and rounding are accounted for.
The 2-Way Formula
Two-way markets are the simplest case, common in tennis, sets in volleyball, or any market with exactly two outcomes. For odds A and B, each stake is calculated as: Stake on A = Total Stake x (1/A) / (1/A + 1/B), and Stake on B = Total Stake x (1/B) / (1/A + 1/B). Your guaranteed return, before rounding, is Total Stake / (1/A + 1/B), the same regardless of which side wins.
The shorter-odds outcome always receives the larger stake, since 1 divided by a smaller decimal odds figure produces a larger weight.
The 3-Way Formula
Three-way markets, most commonly football's 1X2 (home win, draw, away win), extend the same logic across three outcomes instead of two. For odds A, B, and C: Stake on A = Total Stake x (1/A) / (1/A + 1/B + 1/C), and the same pattern for B and C. Your guaranteed return is again Total Stake / (1/A + 1/B + 1/C).
The math scales the same way to four-way or more outcomes, such as correct score or first goalscorer markets, though those are far less commonly arbitrageable since more bookmakers need to disagree simultaneously across more outcomes.
A Worked Example With Real Numbers
Say Bookmaker A offers 2.10 on a home win, Bookmaker B offers 3.60 on the draw, and Bookmaker C offers 4.20 on an away win. The implied probabilities are 1/2.10 = 47.62%, 1/3.60 = 27.78%, and 1/4.20 = 23.81%, adding up to 99.21%, just under 100%, meaning roughly a 0.8% guaranteed margin exists.
With a total stake of 100, you'd place 47.62 on the home win, 27.78 on the draw, and 23.81 on the away win, for a guaranteed return of about 100.80 whichever outcome wins, a profit of roughly 0.80 before accounting for rounding to whatever minimum stake increments your bookmakers allow.
Common Calculator Mistakes That Wipe Out the Margin
Rounding stakes to whole numbers or to a bookmaker's minimum increment can eat a thin margin entirely, so it's worth checking your actual guaranteed return after rounding, not just the calculator's raw output. Mixing up decimal odds with fractional or American odds formats is another common error, since plugging fractional odds directly into a decimal-odds formula will produce a completely wrong stake split.
It's also worth double-checking that all bookmakers are settling the exact same market definition, since 'draw no bet' and a standard 1X2 draw are not interchangeable, and a calculator has no way of knowing you've mismatched them.
Frequently asked
What's the difference between a 2-way and 3-way surebet calculator?
A 2-way calculator splits a stake across two outcomes (like a tennis match winner), while a 3-way calculator splits it across three (like football's home/draw/away). The underlying formula is the same, just extended across more outcomes.
Why does the calculator give me uneven stakes?
Stakes are weighted inversely to each outcome's odds, so the outcome with the shortest price always gets the largest stake. This is what makes your payout identical regardless of which outcome wins.
Can I use a 2-way calculator for a 3-way market?
No, using a 2-way formula on a 3-way market will miscalculate your stakes and payout, since it ignores the third outcome's odds and implied probability entirely.
How do I know if a set of odds is actually arbitrageable?
Add up the implied probability (1 divided by the decimal odds) of every outcome. If the total is below 100%, an arbitrage exists; if it's at or above 100%, there's no guaranteed profit available.
Where can I use these formulas without doing the math by hand?
Our free <a href="/surebets-calculator">sure bets calculator</a> handles both 2-way and 3-way splits automatically, including rounding to your chosen stake increments.