Expected Value Calculator
Enter the price and your own estimated chance of the outcome, and see whether the bet leans positive or negative on average — plus how big that edge actually is.
Key terms, plainly put
Expected value weighs up what a bet is worth on average, over many repeats — not what happens this one time. Put your own estimated chance against the price on offer, and it tells you whether the maths leans your way or the bookmaker's.
The maths behind it
EV = (your probability × profit if it wins) − (chance of losing × stake). Positive means the price pays more than your estimated chance justifies. Negative means the opposite. It only holds up as well as your own estimate does.
Worked example
Odds of 2.50, and you reckon a genuine 45% shot rather than the 40% the price implies. On a £10 stake, expected value comes out around +£1.25 — a small edge in your favour, assuming your 45% holds up.
Breakeven point by price
The probability your own view needs to clear before a bet at that price stops losing money on average. Think the real chance sits above this line — leans positive. Below it — leans negative.
| Decimal odds | Breakeven probability |
|---|---|
| 1.50 | 66.7% |
| 1.91 | 52.4% |
| 2.00 | 50.0% |
| 2.50 | 40.0% |
| 3.00 | 33.3% |
| 4.00 | 25.0% |
| 5.00 | 20.0% |
| 7.50 | 13.3% |
| 10.00 | 10.0% |
| 15.00 | 6.7% |
Common questions
Where does my probability estimate come from?
That part's on you — your own research, model, or judgement. This tool takes whatever number you enter and runs the maths; it doesn't generate the estimate itself.
A positive EV bet still lost — was the maths wrong?
No. EV describes the average outcome across many repeats, not any single result. A positive-EV bet can lose, and a negative-EV bet can win — that's just variance doing its thing.
How different does my estimate need to be from the price to matter?
There's no fixed threshold, but small gaps are easily explained by estimation error. A meaningful, repeatable edge tends to show up as a clear gap, not a rounding difference.