Odds to Probability Calculator
Convert odds into probability and decimal odds.
Results update as you type.
How it works
Odds and probability are two ways of expressing the same likelihood, and this calculator converts odds into a probability percentage and into decimal odds. You enter the odds for an event, the favourable count, and the odds against it, the unfavourable count, and it returns the implied probability and the decimal odds used in betting. Odds stated as, say, one to three mean that for every one favourable outcome there are three unfavourable ones, giving one chance in four, or a 25 percent probability. This differs from probability, which expresses the favourable outcomes as a fraction of the total rather than a ratio against the rest, and the two are easy to confuse. Decimal odds, popular in Europe and in betting exchanges, represent the total return per unit staked including your stake, so decimal odds of four mean a one-unit bet returns four units if it wins. Converting between these forms is essential for anyone comparing gambling odds, assessing risk, or interpreting statistics quoted as odds, such as in medical studies. Being able to translate odds into a plain probability makes their meaning clear. Enter the odds for and against to convert them into probability and decimal odds.
probability = for / (for + against); decimal odds = (for + against) / for
Odds expressed as favourable to unfavourable are converted to probability by dividing the favourable count by the total of both. So odds of one to three mean one favourable outcome out of four total, a probability of 25 percent. Decimal odds, common in betting, are the total divided by the favourable count and represent the payout per unit staked including the stake.
Source:Probability theory (odds)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter odds for (favourable) and odds against (unfavourable).
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Probability updates instantly as you type — no button to press.
Frequently asked questions
What is the difference between odds and probability?
Probability expresses the chance of an event as favourable outcomes divided by the total number of outcomes, while odds express it as the ratio of favourable to unfavourable outcomes. Odds of one to three mean one favourable to three unfavourable, which is a probability of one in four, or 25 percent. They convey the same information in different formats.
How do I convert odds to probability?
Divide the number of favourable outcomes by the sum of favourable and unfavourable outcomes. For odds of two to five, the probability is two divided by seven, about 28.6 percent. The calculator does this automatically when you enter the odds for and against, and it also gives the equivalent decimal odds used in betting.
What are decimal odds?
Decimal odds, common in Europe and betting exchanges, represent the total amount returned per unit staked, including the stake itself. Decimal odds of 4.0 mean a successful one-unit bet returns four units, a three-unit profit plus your original stake. They are found by dividing the total outcomes by the favourable outcomes, and they relate directly to implied probability.
What is implied probability?
Implied probability is the probability suggested by a set of odds, obtained by converting the odds into a percentage. It tells you the likelihood the odds represent. In betting, comparing the implied probability of the odds offered with your own estimate of the true probability is how you judge whether a bet offers value.
Are these gambling odds or statistical odds?
The conversion works for both. Gambling odds and the odds used in statistics, such as odds ratios in medical research, follow the same mathematics of favourable versus unfavourable outcomes. This calculator converts any such odds into a plain probability and decimal odds, making it useful whether you are assessing a bet or interpreting a study that reports results as odds.