Implied probability calculator
Updated
A price is a probability. A prediction market at 62¢ is saying the outcome is about 62% likely, because each share pays $1 if it happens and nothing if it does not. A sportsbook says the same thing as -163. Type any one of them below and the rest follow.
Odds and probability converter
At 62.0%, a winning $1 share pays back $1.61 — a profit of $0.61. A losing share pays nothing, which is the whole of the downside: a share cannot cost you more than you paid for it.
What the bookmaker’s margin costs
Convert both sides of a two-way line and the implied probabilities will sum to more than 100%. The excess is the margin, and it is charged on every stake whether the bet wins or loses. Dividing it out gives the probabilities the prices would state without it.
- Quoted, side A
- 56.5%
- fair 54.3%
- Quoted, side B
- 47.6%
- fair 45.7%
- The book’s cut
- 4.14%
- of every stake, before anyone is right
The two quoted percentages sum to 104.1%. Anything above 100% is the margin, and it is charged whether you win or lose.
This divides the margin proportionally across both sides, which is the standard method and the one other calculators use. It is known to understate the favourite on lopsided markets, so treat the fair probabilities as an estimate rather than as the book’s own view.
The conversions, written out
- Market price to probability
- Divide the price in cents by 100. A market at 62¢ implies 62%.
- Negative American odds
- Divide the number by itself plus 100. -163 becomes 163 / 263 = 62%.
- Positive American odds
- Divide 100 by the number plus 100. +150 becomes 100 / 250 = 40%.
- Decimal odds
- Take the reciprocal. 1.61 becomes 1 / 1.61 = 62%.
- Fractional odds
- Divide the second number by the sum of both. 8/13 becomes 13 / 21 = 62% — a favourite, not an underdog.
Questions
- What does implied probability mean?
- Implied probability is the chance an outcome happens, as read off its price. A prediction market states it directly — a market at 62¢ implies 62% — because each share pays $1 if the outcome happens and nothing if it does not. A sportsbook states the same belief as odds, and the conversion is what this page does.
- How do you convert American odds to a probability?
- For a negative price, divide the number by itself plus 100: -163 becomes 163 / 263, or 62%. For a positive price, divide 100 by the number plus 100: +150 becomes 100 / 250, or 40%. Odds between -100 and +100 are not quoted, because they would imply a probability above 100%.
- Why do a bookmaker's two prices add up to more than 100%?
- The excess is the margin — the hold, or vig. On a two-way market priced -130 / +110, the implied probabilities sum to about 104%, and that 4% is charged on every stake whether the bet wins or loses. Removing it is what the second calculator on this page does.
- Do prediction market prices carry the same margin?
- The two sides of a prediction market sum to roughly 100¢ rather than to a marked-up total, so the equivalent cost is the spread between the buy and the sell price rather than a fixed margin built into the quote. On Papermarkets nothing costs anything at all, because the balance is simulated.
- Is this calculator free?
- Yes, and there is nothing to sign up for. It runs in your browser, sends nothing anywhere, and you are welcome to link to it from your own guide or embed the explanation in your own words.
Try it on a real price
Every market on Papermarkets carries a live price from Polymarket or Kalshi, and you can trade any of them with simulated money. Pick one from the live markets, read the price you just converted, and see what taking a side actually involves. Combining several bets into one is the parlay calculator, which also shows how much the bookmaker’s margin compounds per leg; sizing the position is the Kelly criterion calculator, and two venues disagreeing is the arbitrage calculator. For how much is open at any one time, there is a running count of the whole catalog.