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Probability Calculator

Combine independent event probabilities and find the chance of at least one success over trials.

  • 20%A and B
  • 70%A or B
  • 30%Neither
87.5%

at least one success in those trials

How to use it

  1. Enter two probabilities P(A) and P(B), each between 0 and 1.
  2. Read the combinations A and B, A or B, and neither.
  3. Try repeated trials See the chance of at least one success.

Examples

0.5 and 0.4 A and B = 0.2
1/6, 3 trials ~42%

About this tool

Probability questions get tricky once more than one event is involved. This calculator combines two independent event probabilities to give the chance of both happening, either happening, or neither — the building blocks of most probability problems.

It also answers the common “what’s the chance of at least one?” question across repeated trials, like rolling a six in several throws. Enter probabilities between 0 and 1 and the results update instantly in your browser.

Frequently asked questions

Does this assume independence?

Yes. The combined probabilities assume the events don't affect each other, so P(A and B) is simply P(A) × P(B).

What is "at least one"?

For repeated independent trials, the chance of at least one success is 1 minus the chance of none — 1 − (1 − p) raised to the number of trials.

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Updated June 15, 2026