Probability Calculator
Calculate the basic probability of events.
Tip: Probability is expressed 0–1 or 0–100%. P(A) = favourable outcomes ÷ possible outcomes.
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About this digital tool
The probability calculator determines how likely an event is from the number of favourable outcomes and the total number of outcomes. Enter the two numbers and get the probability as a percentage, as a fraction and as odds (e.g. "1 in 13"). If the favourable outcomes exceed the total, the calculator warns you.
The formula is P = favourable outcomes ÷ total outcomes. Drawing an ace from a 52-card deck has 4 favourable outcomes: P = 4 ÷ 52 = 1/13 ≈ 7.69%. Rolling a die to get a 6 has P = 1/6 ≈ 16.67%. Probability is always between 0 (impossible) and 1 (certain). It is used in games, statistics, insurance and decision-making.
How to use
- Enter the number of favourable outcomes, that is the results you are interested in.
- Enter the number of total outcomes, that is all possible results.
- Read the probability as a percentage and as a fraction.
- See the "1 in ..." odds to understand it more easily.
Frequently asked questions
How is the probability of two independent events calculated?
P(A and B) = P(A) × P(B). E.g. two dice both rolling 6: (1/6) × (1/6) = 1/36 ≈ 2.78%.
How is the probability of an event calculated?
Divide the number of favourable outcomes by the total number of outcomes. E.g. to get an even number on a die: 3 outcomes (2, 4, 6) out of 6, so P = 3/6 = 50%.
What is the probability that the event doesn't happen?
It is 1 minus the probability of the event. If P(6) = 1/6, then the probability of not rolling a 6 is 1 − 1/6 = 5/6 ≈ 83.33%.
What do probabilities 0 and 1 mean?
0 means an impossible event, 1 (or 100%) a certain event. Every other event has a probability between them.