Probability to Odds Calculator

Convert a probability given as a percentage into odds against and European decimal odds.

Odds against
1 : 3.00
For every time it happens, it doesn't happen 3 times
Probability
25.0 %
Decimal odds (European format)
4.00
Embed on your website →

How to use the probability and odds calculator

  1. Enter the probability that something happens, as a percentage (between 0.01 and 99.99).
  2. The calculator automatically converts to "odds against" and European decimal odds.
  3. Use the result to compare or understand how probability is expressed in different formats.

How probability converts to odds

Probability is expressed as a percentage between 0 and 100%, telling you how large a share of cases something is expected to happen. Odds express the same relationship differently — as a ratio between "happens" and "doesn't happen":

Odds against: (100 − P) ÷ P, shown as "1 : X"
Decimal odds: 100 ÷ P

Decimal odds are the format often used in European sports betting. The number shows the potential payout per unit staked, including the stake itself — decimal odds of 4.00 means a 1-unit stake returns 4 units if the outcome occurs.

Note: This is a mathematical tool for converting between probability and odds formats — it is not an endorsement of or guide to gambling. Gamble responsibly, and never bet more than you can afford to lose.
Ad space — reserved for future partners

Frequently asked questions

What's the difference between probability and odds?

Probability is expressed as a percentage of all possible outcomes, for example 25%. Odds express the same thing as a ratio between something happening and not happening, for example "1 : 3" — both describe the same chance, just in different ways.

What does "decimal odds" mean?

Decimal odds are an odds format often used in Europe. The number shows the total payout per unit staked if the outcome occurs, including the stake itself. Decimal odds of 2.00 means double your stake back.

How do I convert odds back to probability?

Divide 100 by the decimal odds to find the probability as a percentage. With decimal odds of 4.00, the probability becomes 100 ÷ 4 = 25%.

Embed this calculator on your website

Copy the code below to show this calculator directly on your blog or website — completely free.