Implied Probability: How to Turn Betting Odds into Percentages
Every price is a probability in disguise. Here’s how to convert American, decimal and fractional odds, and what the number tells you.
The Smart Lines teamOctober 20264 min read
What implied probability is
Implied probability is the chance of winning that a price represents. It’s also your break-even rate: the share of bets like this one you need to win just to break even at that price. If you think a team wins more often than its implied probability, the price looks good to you; if less often, it doesn’t.
How to convert odds to implied probability
American odds
- Negative odds (favourites):
implied = odds ÷ (odds + 100), using the number without its minus sign. −200 is 200 ÷ 300 = 66.67%. - Positive odds (underdogs):
implied = 100 ÷ (odds + 100). +250 is 100 ÷ 350 = 28.57%.
Decimal odds
implied = 1 ÷ decimal odds. Decimal 2.50 is 1 ÷ 2.50 = 40%. This is the format most Canadian sportsbooks show by default, and it’s the easiest to work with.
Fractional odds
For odds of A/B: implied = B ÷ (A + B). 5/2 is 2 ÷ 7 = 28.57%, the same as +250.
| American | Decimal | Implied probability |
|---|---|---|
| −200 | 1.50 | 66.67% |
| −110 | 1.91 | 52.38% |
| +100 | 2.00 | 50.00% |
| +150 | 2.50 | 40.00% |
| +250 | 3.50 | 28.57% |
The implied odds calculator does these conversions for any price, and the odds converter switches between formats.
Why both sides add up to more than 100%
Convert both sides of almost any bet and they’ll sum to more than 100%. A game at −110 / −110 implies 52.38% + 52.38% = 104.76%. The extra 4.76% is the sportsbook’s margin, also called the vig. Implied probability therefore overstates each side’s true chance a little.
To get each side’s fair chance, remove the margin first. Our guide to no-vig odds shows two ways to do it.
Example
Is +150 a good price?
+150 implies 40%. Suppose the sharpest prices in the market, with the margin removed, give the team a 42% chance. You’d be paid as if the team wins 40% of the time when it really wins 42% of the time:
- Break-even rate at +150
- 40.0%
- Fair chance of winning
- 42.0%
- Expected value: 0.42 × 2.50 − 1
- +5.0%
That gap between the fair chance and the price’s implied probability is exactly what expected value measures.
The short version
- Implied probability is the break-even win rate for a price.
- Decimal: 1 ÷ odds. American minus: odds ÷ (odds + 100). American plus: 100 ÷ (odds + 100).
- Both sides add up to over 100%; the excess is the book’s margin.
- A bet is +EV when its fair chance of winning is above its implied probability.