Probability Calculator

Combine the probabilities of two independent events, or find the chance something happens at least once over repeated tries.

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Between 0 and 1 (0.5 = 50%)
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How to use this calculator

Enter your values after choosing the type of calculation in the tabs. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.

Formulas (independent events)

P(A and B) = P(A) × P(B) P(A or B) = P(A) + P(B) − P(A) × P(B) P(neither) = (1 − P(A)) × (1 − P(B)) P(at least once in n tries) = 1 − (1 − p)ⁿ

These assume the events don’t affect each other (independence). For dependent events, use conditional probabilities. Example: a 10% chance per try gives 1 − 0.9¹⁰ ≈ 65.1% of at least one success in 10 tries, not 100%.

Frequently asked questions

What is the probability of rolling at least one 6 in 4 rolls?

1 − (5/6)⁴ ≈ 51.8%.

About this tool

Written by
[Author: to be assigned]
Reviewed by
Formula tests passed · human review pending
Last updated
31 Oct 2026

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