How to use the odds to probability calculator
- Choose what you have: fractional odds, decimal odds, American odds or a probability in percent.
- Type the value. Examples: 5/2 or 5-2 for fractional, 3.5 for decimal, +250 or -150 for American, and 28.57 for a probability.
- Open the advanced options to change the example stake used for the profit line. It does not affect the conversion.
- Read the implied probability, the same odds in every format, the odds against and in favor, and the profit and total return on the stake.
Formula
profit per 1 staked: fractional a/b gives a/b, decimal d gives d - 1
American +A gives A/100, American -A gives 100/A
probability = 1 / (1 + profit per 1 staked)
decimal odds = 1 + profit per 1 staked
All conversions use exact fractions, so 28.57% becomes 7143/2857 rather than a rounded decimal. American odds are +100 times the profit per unit when it is at least 1, and -100 divided by the profit per unit otherwise.
Odds of 5/2
Fractional odds of 5/2 mean a profit of 5 for every 2 staked, or 2.5 per 1. The probability is 1 / (1 + 2.5) = 28.5714%, the decimal odds are 3.5 and the American odds are +250. A $10 stake would earn $25 profit and return $35 in total.
American -150 means risking 150 to win 100, a profit of 2/3 per unit. The probability is 1 / (1 + 2/3) = 60%, the fractional odds are 2/3 and the decimal odds are 1.6667. A probability of 25% converts the other way: the profit per unit is 75 / 25 = 3, so odds of 3/1, decimal 4 and American +300.
What each format means
Fractional odds such as 5/2 state the profit relative to the stake. Decimal odds state the total return per unit staked, stake included. American odds use a base of 100: a plus number is the profit on a 100 stake, and a minus number is the stake needed to make a 100 profit.
All three describe the same bet. The implied probability is the chance at which the bet would break even, which is why it equals the stake divided by the total return.
Implied probability is not a forecast
A set of odds from a bookmaker or a market includes a margin, so the implied probabilities of all outcomes add up to more than 100%. The converted figure is therefore a little higher than a fair estimate of the chance. Converting odds does not say what will happen, and no result here is advice to place a bet.
For chances built from counted outcomes, use the probability calculator, for poker decisions the pot odds calculator, and to weigh payoffs against chances the expected value calculator.
Assumptions and limits
- The conversion treats the entered value as exact. Odds with more than 18 digits are refused.
- American odds below 100 in size do not exist in the format, so values like +50 or -50 are rejected.
- Decimal odds must be greater than 1, and a probability must be above 0% and below 100%.
- The stake line is an example amount. Taxes, fees, commissions and betting margins are not modeled.
Frequently asked questions
How do I turn odds into a percentage?
Convert the odds to profit per unit staked, then use probability = 1 / (1 + profit per unit). For 5/2 that is 1 / 3.5 = 28.57%. The page does this for fractional, decimal and American odds.
What is the difference between odds for and odds against?
Odds against compare misses with hits, so 5 to 2 against means 5 misses for every 2 hits. Odds in favor flip the order. The page shows both for the odds you enter.
Why does even money show as +100 and 2.0?
Even money pays a profit equal to the stake. That is 1/1 fractional, 2.0 decimal and +100 American, and the implied probability is exactly 50%.
Can I enter a probability and get odds?
Yes. Choose A probability, type a percent such as 25, and the page returns the fractional, decimal and American odds that would pay out fairly at that chance.