Market analysis
Expected value (EV) calculator
Expected value
Expected value (EV)
If your own estimated probability differs from the one implied by the odds, that gap can be quantified: EV = probability × odds − 1.
Enter your own probability estimate (0–100%) and the quoted odds.
The formula
EV = probability × odds - 1. Break-even probability: 1 / odds.
Worked example
Say you estimate an outcome at 45% and the odds are 2.50. EV = 0.45 × 2.50 - 1 = 0.125, i.e. +12.5% per unit staked. The break-even point is 1/2.50 = 40%: above a true 40% chance the mathematical expectation is positive, below it negative. Every part of the calculation rests on the 45% estimate: if the true chance is only 38%, the actual EV is -5%.
Reference point: what does the market say?
Our own research across more than 50,000 matches from 11 seasons found the bookmakers' closing prices more accurate than every model we tested. In practice a positive EV signal therefore usually means your estimate differs from the market, not that the market is wrong. On top of that, 100 bets at odds around 2.00 produce roughly ±20% of ROI swing from variance alone, with no skill involved.
Common misunderstanding
The most common mistake is treating EV as an objective property of the bet. It measures the relationship between your estimate and the price: with an inaccurate probability, positive EV exists only on paper. Short-term results neither confirm nor refute it: on a small sample, profit is mostly noise, not evidence.
What does positive EV mean?
That with the given probability estimate and odds, the formula returns a positive mathematical expectation per unit staked. This stands or falls with the accuracy of the estimate: the formula cannot check whether the probability you enter is sound.
What is the break-even probability?
The hit rate at which the given odds break even in the long run: 1/odds. At odds of 2.50 it is 40%, i.e. four hits out of ten are needed to break even.
Where should the probability come from?
That is the hard part; the formula itself is just arithmetic. A starting point can be the implied probability computed from market prices with the margin removed: our research shows the market's closing price is a very strong long-run reference.
Does positive EV guarantee a profit?
No. The estimate may be inaccurate, and even with an accurate one, variance produces long losing streaks: on a sample of about 100 bets the ROI can swing by roughly ±20 percentage points purely from noise.
How does EV relate to value betting?
A value bet is the situation where the estimated probability is higher than what the odds reflect, i.e. the formula returns a positive EV. In practice this means anything only if the estimate is more accurate than the market, which our measurements show is rare.