Price the edge before you bet it.
Enter the price you are being offered and the win probability you believe is fair. The calculator returns the expected value per $100 and the break-even rate the price demands.
How expected value works
EV is the long-run average of a bet. Take the probability you win times what you win, subtract the probability you lose times what you lose. At -110 with a 55% fair probability, that is 0.55 × $90.91 minus 0.45 × $100 — exactly +$5.00 per $100 staked. One number, and it already contains everything the price and your probability have to say.
Break-even is the bar the price sets. Every American price implies a win rate at which it returns exactly nothing: 52.4% at -110, 50% at +100, 60% at -150. Your fair probability either clears that bar or it does not. The margin above the bar — not the price itself — is what you get paid for.
The fair probability is the honest input. It comes from your model or from a devigged market — the vig calculator strips the juice from any two-sided quote. The output is only as good as this input; the calculator measures your disagreement with the price and cannot manufacture an edge you do not have.
Positive EV pays over volume, not tonight. A +5% edge loses routinely in small samples; variance owns the short run. The edge shows up across hundreds of prices, which is why serious bettors track every pick and watch closing-line value — the fastest evidence the number was right — rather than the last score.
How the calculator works
01
Your price converts to a break-even probability — the bar the odds set.
02
Your fair probability is compared against that bar.
03
The gap, times the payout, is your expected value per unit staked.
Expected value questions
- How is expected value calculated?
- EV = p × profit − (1 − p) × stake. At +100 with a 55% fair probability: 0.55 × 100 − 0.45 × 100 = +$10 per $100 staked. The calculator runs the same arithmetic for any American price and any probability you supply.
- What win probability should I enter?
- The number you actually believe — from a model, or a fair price devigged from a sharp market. Enter the book’s own implied probability and EV reads zero by construction; the tool measures your disagreement with the price, not the price itself.
- What does break-even probability mean?
- The win rate at which your price neither makes nor loses money over time. A -110 price breaks even at 52.4%. If your fair number clears that bar the bet is positive EV; below it, you are paying for action.
- Is positive EV a guarantee?
- No. EV is a long-run average and short samples are ruled by variance. The discipline is taking positive-EV prices repeatedly and letting volume work — closing-line value is the fastest signal that you are on the right side of the number.
Betting an edge you just priced? Track it and we will grade the pick against the closing line.