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Odds Calculator

Created by Bogna Szyk and Steven Wooding
Reviewed by Dominik Czernia, PhD and Jack Bowater
Last updated: Jan 18, 2024

If you ever wondered about your chances of winning a bet with odds 3 to 5, our odds calculator is here to help you. Having given the betting odds, you will now be able to calculate the percentage probability of winning or losing and decide whether the reward is worth the risk. You will also find out how to calculate the odds ratio using the odds equation.

What are the odds...?

The odds are usually presented as a ratio. For example, the odds of your favorite football team losing a match maybe 1 to 5. The odds of you winning a lottery might by 1 to 10,000. On the other hand, the odds of the horse you bet on winning the race may be equal to 4 to 3.

What do these numbers mean? There are two types of odds ratios: "odds of winning" and "odds of losing". For odds of winning, the first number is the chances for success, and the second is the chances against success (of losing). For "odds of losing", the order of these numbers is switched.

How to calculate odds

Our betting odds calculator takes a step further and calculates the percentage probability of winning and losing. The team would win 5 out of 6 games and lose 1 of them. By converting fraction to percent, we can say that the chances of winning are 5/6 = 83.33%, and of losing 1/6 = 16.67%.

Do you understand how we calculated this percentage? If not, take a look at the odds formulas:

probability of winning = chances for success / all chances

probability of losing = chances against success / all chances

all chances = chances for success + chances against success

How to use the odds ratio calculator: an example

  1. Find out what the odds are expressed as a ratio. Let's say that the odds of you winning in a school lottery are 5 to 12.
  2. Decide which number represents chances for success (for winning), and which number represents chances against success (for losing). In this case, there are five chances for success and 12 chances against success.
  3. Sum up all of the chances: 5 + 12 = 17.
  4. Calculate the probability of winning according to the odds formulas: 5/17 = 29.41%.
  5. Calculate the probability of losing according to the odds formulas: 12/17 = 70.59%.
  6. Check whether the result is correct with the betting odds calculator.


What are one to five odds of losing?

If the odds for a football team losing are 1 to 5, it means that there are five chances of them winning and only 1 of them losing. That means that if they played six times, they would win five times and lose once.

How do I convert odds to probability?

To calculate probability given odds, first you need to know if the odds are in favor or against:

  • if x : y are odds in favor, then:
    probability = x / (x + y)

  • if x : y are odds against, then:
    probability = y / (y + x)

Example: If odds are 4:1 in favors, then probability is 4 / (4 + 1) = 4/5 = 80%.

How do I convert probability to odds?

To calculate odds given probability, you need to divide the probability by one minus the probability:

odds = probability / (1 - probability)

Remember to replace 1 by 100% if the probability is given as a percentage.

Example: If probability is 25%, then odds are is 25% / 75% = 1/3 = 0.33.

How do I calculate odds ratio?

To calculate odds ratio for some event, you need to:

  1. Determine the probability that the event will occur.

  2. Compute the probability that the event will not occur: if the probability of it occurring is p, then the probability of it not occurring is 1 - p.

  3. Divided the probability that the event will occur by the probability that it will not occur:

    Odds ratio = p / (1 - p)

Example: If p = 20%, then 1 - p = 80% and Odds ratio = 20% / 80% = 1/4 = 0.25.

Bogna Szyk and Steven Wooding
Related calculators
Chances for success
Chances against success
Probability of winning
Probability of losing
Odds conversions
Fractional odds:
Decimal odds
American (moneyline odds)
Total returned
Potential net profit
Disclaimer: Omni Calculator does not recommend any form of betting.
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