Free tool · Odds
Odds converter
Type odds in any box and every other format updates: American, decimal, fractional, implied probability, and the matching Kalshi or Polymarket price.
The three odds formats
All three formats describe the same thing: how much a winning bet pays. They just write it differently, depending on where you bet.
- American odds (US sportsbooks). A plus sign shows what you win on a $100 stake: +150 wins $150. A minus sign shows what you must stake to win $100: −120 means stake $120 to win $100.
- Decimal odds (Europe, Canada, Australia, betting exchanges). The total return for each $1 staked, including your stake: 2.50 returns $2.50 for $1.
- Fractional odds (UK and Ireland). Profit over stake: 3/2 wins $3 for every $2 staked. "Evens" is 1/1.
Conversion formulas
American to decimal
Decimal to American
Fractional to decimal
Odds to implied probability
Implied probability is the chance the price suggests, not the true chance. A sportsbook builds its margin into the prices, so the implied probabilities of every outcome in a market add up to more than 100%.
Common odds, converted
| Fractional | Decimal | American | Implied probability |
|---|---|---|---|
| 1/5 | 1.20 | −500 | 83.3% |
| 1/4 | 1.25 | −400 | 80.0% |
| 2/7 | 1.29 | −350 | 77.8% |
| 1/3 | 1.33 | −300 | 75.0% |
| 2/5 | 1.40 | −250 | 71.4% |
| 1/2 | 1.50 | −200 | 66.7% |
| 4/7 | 1.57 | −175 | 63.6% |
| 8/13 | 1.62 | −163 | 61.9% |
| 4/6 | 1.67 | −150 | 60.0% |
| 4/5 | 1.80 | −125 | 55.6% |
| 10/11 | 1.91 | −110 | 52.4% |
| Evens (1/1) | 2.00 | +100 | 50.0% |
| 11/10 | 2.10 | +110 | 47.6% |
| 6/5 | 2.20 | +120 | 45.5% |
| 5/4 | 2.25 | +125 | 44.4% |
| 6/4 | 2.50 | +150 | 40.0% |
| 7/4 | 2.75 | +175 | 36.4% |
| 2/1 | 3.00 | +200 | 33.3% |
| 5/2 | 3.50 | +250 | 28.6% |
| 3/1 | 4.00 | +300 | 25.0% |
| 4/1 | 5.00 | +400 | 20.0% |
| 5/1 | 6.00 | +500 | 16.7% |
| 7/1 | 8.00 | +700 | 12.5% |
| 10/1 | 11.00 | +1000 | 9.1% |
Bookmaker margin and fair odds
Enter both sides of a two-way market, in any format. The tool shows how much margin the book has built in, and the fair odds once that margin is removed. If the two sides add up to less than 100%, the prices come from different books and you have found an arbitrage.
American (−110, +150), decimal (1.91) or fractional (10/11). The format is detected for you.
Prediction market prices as odds
On Kalshi and Polymarket, a contract pays $1 if its outcome happens, so the price in cents is the implied probability. A contract at 40¢ is decimal odds of 1 / 0.40 = 2.50, or +150. Both platforms charge a trading fee on top of the price, which lowers the odds you really get. For the after-fee numbers, use the Kalshi arbitrage calculator, and see Kalshi fees explained.
Using converted odds for arbitrage
Arbitrage starts with the same step this converter does: turning every price into an implied probability. When the best prices for each outcome, from different books, add up to less than 100%, you can cover every outcome and lock in a margin. The arbitrage calculator takes American or decimal odds and splits your stake for you.
Found two prices that disagree? Size both bets.
Open the arbitrage calculatorFAQ
How do you convert American odds to decimal odds?
For positive American odds, divide by 100 and add 1: +150 becomes 2.50. For negative American odds, divide 100 by the number without its minus sign and add 1: −120 becomes 1.83.
What does −110 mean in betting?
−110 means you stake $110 to win $100, which is decimal odds of 1.91 and an implied probability of 52.4%. When both sides of a game are −110, the two probabilities add up to 104.8%, and the extra 4.8% is the sportsbook's margin.
How do you convert odds to implied probability?
Divide 1 by the decimal odds. Decimal odds of 2.50 are 1 / 2.50 = 40%. For American or fractional odds, convert to decimal first.
What are evens in betting?
Evens, written 1/1 in fractional odds, means you win the same amount you stake. It is decimal odds of 2.00, American odds of +100 and an implied probability of 50%.
How do Kalshi and Polymarket prices compare to odds?
A prediction market price in cents is the implied probability. A contract at 40¢ pays $1 if it wins, which is decimal odds of 1 / 0.40 = 2.50, or +150 in American odds, before fees.