CONVERTER
Odds converter
Enter odds in any format and the rest update at once: decimal, American, fractional and implied probability. A Polymarket or Kalshi contract price in cents equals the probability in percent.
The probability includes the bookmaker’s margin. A Polymarket or Kalshi contract price in cents equals the probability in percent.
Odds conversion table
| Decimal | American | Fractional | Probability, % · price, ¢ |
|---|---|---|---|
| 1.20 | -500 | 1/5 | 83.33 |
| 1.50 | -200 | 1/2 | 66.67 |
| 1.80 | -125 | 4/5 | 55.56 |
| 1.90 | -111 | 9/10 | 52.63 |
| 2.00 | +100 | 1/1 | 50 |
| 2.50 | +150 | 3/2 | 40 |
| 3.00 | +200 | 2/1 | 33.33 |
| 4.00 | +300 | 3/1 | 25 |
| 5.00 | +400 | 4/1 | 20 |
| 10.00 | +900 | 9/1 | 10 |
How to use the converter
- Type the odds into the field of your format: decimal 2.50, American +150 or −200, fractional 3/2, probability 40.
- The other fields update at once. You can edit any field: the last one you changed becomes the reference.
- For Polymarket and Kalshi, enter the contract price in cents in the probability field: a 40¢ contract equals odds of 2.50 before fees.
Conversion formulas
The reference format is decimal odds K. American: for K ≥ 2 it is +(K − 1) × 100, for K < 2 it is −100 / (K − 1); back again, +A → 1 + A/100, −A → 1 + 100/A. Fractional a/b is the net win per stake: K = 1 + a/b. Probability is 100 / K percent. Examples: 2.50 = +150 = 3/2 = 40%; 1.50 = −200 = 1/2 = 66.67%; −110 = 1.909 = 10/11 = 52.38%.
What to keep in mind
- The probability implied by the odds includes the bookmaker’s margin: the probabilities of all outcomes add up to more than 100%. The margin calculator gives the fair probability.
- Fractional odds are approximated with a denominator up to 100, so non-standard odds are rounded.
- Polymarket and Kalshi prices are converted without fees or spread; fees are covered in a separate article.
- American odds between −100 and +100 do not exist, and the converter rejects such values.
Formats get mixed when a surebet spans a bookmaker and a prediction market. The Dozor scanner converts bookmaker, Polymarket and Kalshi lines to decimal odds itself, and the surebet calculator splits the stakes.
FAQ
How do you convert American odds to decimal?
Positive: 1 + A/100, for example +150 → 2.50. Negative: 1 + 100/|A|, for example −200 → 1.50, −110 → 1.909.
How do you convert odds to probability?
Divide 100 by the decimal odds: 2.50 → 40%, 1.90 → 52.63%. This probability still includes the bookmaker’s margin.
How do you convert a Polymarket price to odds?
The contract price in cents is the probability in percent. Odds = 100 / price: 40¢ → 2.50, 65¢ → 1.538. Fees and spread lower the real odds.
What do fractional odds of 5/2 mean?
A win of 5 for every 2 staked, on top of the stake returned. Decimal odds = 1 + 5/2 = 3.50, probability 28.57%.
Other free tools
- Surebet calculator — up to 10 outcomes, exchange commission, a fixed leg and ROI
- Bookmaker margin calculator — margin, probabilities and fair odds
- Dutching calculator — stakes on several outcomes with the same return
- Hedge calculator — hedge stake and profit whatever the outcome
- Kelly calculator — share of the bankroll, stake and EV