Odds converter
Convert odds between any format.
Last updated 2026-07-03
Type odds in any one field: American, decimal, or fractional. The other formats and the implied probability update instantly. All math runs in your browser.
The formulas
American to decimal: positive odds: 1 + odds/100 (+150 = 2.50). Negative odds: 1 + 100/|odds| (-110 = 1.909).
Decimal to implied probability: 1 / decimal. 2.50 implies 40%.
Fractional: profit over stake. 3/2 = decimal 2.50 = +150.
Remember: a single book's implied probability includes vig. To recover the market's true probability, use the no-vig calculator with both sides of the market.
Do this programmatically
TheOddsAPI serves both American and decimal natively. One parameter, no conversion code:
curl "https://api.theoddsapi.com/odds/?sport_key=baseball_mlb&oddsFormat=decimal" \ -H "x-api-key: YOUR_API_KEY"
Works on /odds/, /best-lines/, /props/, /historical/odds, and /edges/. Free key in minutes, no credit card.
Questions
Why do implied probabilities across a market sum to more than 100%?
That excess is the bookmaker's margin (vig). A typical NBA moneyline at -110 both ways implies 52.4% + 52.4% = 104.8%; the 4.8% is the book's hold.
Which format should I use for modeling?
Decimal. It multiplies cleanly for parlays, converts to probability with one division, and avoids the sign discontinuity American odds have between +100 and -100.
More tools: No-vig fair odds · Arbitrage · CLV · Parlay