Prediction Market Odds Converter for Kalshi & Polymarket
Convert market prices to American, decimal, fractional odds, and implied probability.
American odds to decimal odds conversion chart
These common lines also work in reverse as a Kalshi or Polymarket odds converter: a 40¢ contract is +150 American odds, 2.50 decimal odds, and 3/2 fractional odds.
| Market price | American | Decimal | Fractional | Implied probability |
|---|---|---|---|---|
| 20¢ | +400 | 5.00 | 4/1 | 20% |
| 25¢ | +300 | 4.00 | 3/1 | 25% |
| 40¢ | +150 | 2.50 | 3/2 | 40% |
| 50¢ | +100 | 2.00 | 1/1 | 50% |
| 60¢ | -150 | 1.67 | 2/3 | 60% |
| 67¢ | -203 | 1.49 | 1/2 | 67% |
| 75¢ | -300 | 1.33 | 1/3 | 75% |
| 80¢ | -400 | 1.25 | 1/4 | 80% |
What does this calculator do?
The odds converter translates between the formats you'll encounter across prediction markets and sportsbooks: American moneyline odds (e.g., −110 or +230), decimal odds (e.g., 1.91 or 3.30), fractional odds (e.g., 10/11 or 2/1), and implied probability (e.g., 60%). Each format encodes the same information — the price of a position — but in ways that are not immediately comparable without conversion.
Prediction markets like Kalshi and Polymarket quote prices as implied probability — a contract at 0.63 costs 63 cents and pays $1 if it resolves YES. Sportsbooks use American or decimal odds. When you're trying to compare a Polymarket price against a sportsbook line on the same event, you need to convert to a common format to see which is offering better value. To compare the prediction market venues against each other, the odds screen shows every venue's price for each game side by side, in cents, implied probability or decimal odds.
Enter any one format and the calculator instantly outputs every other format. The math is straightforward: implied probability = 1 / decimal odds; American odds for favorites = −(probability / (1 − probability)) × 100; for underdogs = ((1 − probability) / probability) × 100. The converter handles edge cases like exactly 50% (+100 moneyline) and near-certainty contracts cleanly.
Note that these conversions assume no vig — they treat the quoted price as the true probability. In practice, quoted prices contain a built-in margin. Use the No-Vig calculator after converting to strip that margin out and find the fair probability on each side.