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.
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.