Implied Probability Calculator
Enter every side of a market to see the total implied probability and the bookmaker's vig.
How To Use This Calculator
Turn any odds into a win percentage in a few seconds.
Switch between American, decimal, and fractional. It opens on your saved odds format.
Type the price for the outcome you want. The implied probability updates as you type.
Add both sides of a market to see each win % and the total overround, or vig.
What is implied probability?
Implied probability is the win chance built into a set of odds, written as a percentage. Decimal odds of 2.00 imply a 50% chance, and American odds of -110 imply roughly 52.38%. It is simply the odds expressed a different way.
It reflects the price a book is offering, not the real likelihood of the outcome. Because the odds still include the bookmaker's margin, implied probability always overstates the true chance by a little. Removing that margin is called devigging.
Implied probability formulas
The math depends on the odds format. Each formula returns a probability you can read as a percentage.
Positive American odds: 100 / (odds + 100). Example: +150 gives 100 / 250 = 40%.
Negative American odds: |odds| / (|odds| + 100). Example: -200 gives 200 / 300 = 66.67%.
Decimal odds: 1 / decimal. Example: 2.50 gives 1 / 2.50 = 40%.
Fractional odds a/b: b / (a + b). Example: 1/2 gives 2 / 3 = 66.67%.
Why odds add up to more than 100%
Add the implied probability of every outcome in a market and a fair market totals 100%. Real markets total more. Two -110 sides imply 52.38% each, so the market adds up to about 104.76%. That extra 4.76% is the overround, the margin the book keeps.
To see the fair price with the margin stripped out, remove the vig with the no-vig calculator and compare it against the odds you can actually bet.
Common Mistakes to Avoid
The odds still contain the vig, so implied probability is always a touch high. Devig before you trust the number.
Positive and negative American odds use different formulas. Include the sign so the calculator applies the right one.
Comparing one side's implied probability without checking the full market hides how much margin is priced in.
Frequently Asked Questions
What is implied probability in betting?
Implied probability is the win chance baked into a set of odds, expressed as a percentage. Decimal odds of 2.00 imply 50%, and American -110 implies about 52.38%. It reflects the book's price and still includes the vig.
How do you convert American odds to implied probability?
For positive odds, 100 / (odds + 100): +150 becomes 40%. For negative odds, |odds| / (|odds| + 100): -200 becomes 66.67%.
Why do the probabilities add up to more than 100%?
A fair market sums to 100%. The excess is the overround, or vig, that the book builds in. Two -110 sides total about 104.76%, so the vig is 4.76%.
Implied probability vs true probability?
Implied probability comes from the odds and includes the vig, so it overstates the real chance. True probability is what remains after the vig is removed by devigging.
How do I convert implied probability back to fair odds?
Remove the vig, then divide 100 by the fair probability to get fair decimal odds. The no-vig calculator handles two-way and three-way markets.
Pro tip
Implied probability tells you the price. To know whether a bet is worth taking, compare it against your own estimate with the expected value calculator and bet only when the edge is positive.