Betting math, before the book takes your money
Five free calculators that answer the only question that matters about any bet: is this price worth taking? Type the odds you're seeing — American (−110) or decimal (1.91) — and get the vig, the fair line, the expected value, the arb check, and the right stake. All math runs server-side, same as every ranking on this site.
| Tool | What it tells you |
|---|---|
| No-vig calculator | The fair line and true probability once the book's margin is stripped out. |
| EV calculator | What a bet is worth in dollars, its ROI, and the break-even win rate. |
| Arbitrage calculator | Whether two prices lock in a profit, and the exact stake on each side. |
| Kelly calculator | The bankroll-optimal stake for your edge — full, half, and quarter Kelly. |
| Odds converter | American ↔ decimal ↔ fractional ↔ implied probability, instantly. |
Why these five numbers beat gut feel
- Every price implies a probability. −110 says 52.4%, +200 says 33.3%. The book's margin hides in those numbers summing past 100% — the no-vig calculator shows what the market really believes.
- EV is the whole game. Long-run profit is just edge × volume. If you can't say what a bet's EV is, the book can — and priced it so theirs is positive.
- Stake size is a math problem, not a mood. Kelly turns your edge into a stake; betting more than Kelly with an overestimated edge is the fastest route to zero.
Frequently asked questions
What is expected value (EV) in sports betting?
EV is what a bet is worth on average: win probability × profit minus lose probability × stake. A +EV bet pays more than the true odds require. Every calculator here exists to tell you that number before the book takes your money.
What does "no-vig" or "fair line" mean?
Books price both sides so the implied probabilities sum past 100% — the excess is their margin (the vig). Removing it reveals the market's actual opinion, the fair line. Beating the fair line at another book is the core of profitable betting.
Are these calculators free?
Yes — all the math runs on this page with numbers you type in. No account, no feed, no upsell. The daily best-lines snapshot, when shown, is refreshed each morning and timestamped — always verify a line before betting it.
Tools compute standard formulas on numbers you provide; snapshot lines (when shown) are dated and can be stale. Nothing here is a prediction or betting advice. 21+ where applicable; sports betting is legal only in some states. Gambling problem? Call 1‑800‑GAMBLER.