About the Probability Calculator
Find the chance of two independent events happening together or separately. This tool is free, works in your browser and needs no sign-up.
How to use the Probability Calculator
Enter the probability of event A and event B as numbers from 0 to 1.
Formula used
Both = P(A) × P(B). Either = P(A) + P(B) − P(A) × P(B). Neither = (1 − P(A)) × (1 − P(B)).
Example
With P(A) from 0 to 1 0.5, P(B) from 0 to 1 0.3, the calculator shows: A and B both happen = 0.15; A or B (at least one) = 0.65; Neither happens = 0.35.
Frequently asked questions
Is the Probability Calculator free to use?
Yes. It is completely free and you can use it as many times as you like.
How accurate is the Probability Calculator?
The calculator uses standard formulas, so the maths is exact. Real life results can differ because of fees, taxes, rounding or personal factors, so treat the answer as an estimate.
Do you store the numbers I enter?
No. All calculations run in your browser. The values you type are not sent to our server.
Disclaimer: results are estimates for information only. They are not financial, medical or professional advice.