How do I calculate a single event probability?

Divide favorable outcomes by total equally likely outcomes. One desired face on a six-sided die has probability 1/6.

What does AND mean in probability?

For independent events, AND means both happen, so multiply their probabilities.

What does OR mean for independent events?

OR means at least one happens. Add both probabilities, then subtract the probability that both happen.

Can I use the two-event mode for dependent events?

No. It assumes independence. Use conditional probability when one event changes the likelihood of the other.

Math Calculators

Probability Calculator

Calculate single-event probability or combine two independent events with AND or OR.

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Favorable outcomesTotal outcomes

Probability

0.166666666667

16.6666666667%Not: 0.833333333333For: 1:5Against: 5:1

Glossary

Probability: How likely an event is, from 0 (never) to 1 (certain).
Favorable outcomes: The results you are counting as a success.
Total outcomes: Every possible result that could happen.
Independent events: Events where one happening does not change the odds of the other.
A and B: The chance that both events happen (multiply the two probabilities).
A or B: The chance that at least one of the events happens.

About the Probability Calculator

For equally likely outcomes, probability is the number of favorable outcomes divided by the total possible outcomes. The result can be written as a decimal, percentage or odds.

Single-event mode also shows the complement, odds for and odds against. Independent-events mode calculates the probability that both events occur or that at least one occurs.

The two-event formulas assume independence, meaning one event does not change the probability of the other. Dependent events require conditional probability and should not use this mode.

Key features

Decimal and percentage probability
Complement and simplified odds
Independent AND probability
Independent OR probability

How to use

1Choose Single event or Two independent events.
2Enter outcomes or probabilities from 0 to 1.
3Select AND or OR when combining events and read the result.

Examples

Single event probability

Input: 3 favorable of 6 outcomes

Output: 0.5 (50%)

Favorable outcomes divided by total outcomes gives the probability.

Frequently asked questions

How do I calculate a single event probability?: Divide favorable outcomes by total equally likely outcomes. One desired face on a six-sided die has probability 1/6.
What does AND mean in probability?: For independent events, AND means both happen, so multiply their probabilities.
What does OR mean for independent events?: OR means at least one happens. Add both probabilities, then subtract the probability that both happen.
Can I use the two-event mode for dependent events?: No. It assumes independence. Use conditional probability when one event changes the likelihood of the other.

Open a related tool to prepare your files or refine the finished result.