Calculators

How to Use the Probability Calculator

2026-11-124 min readBy Apex Tool Station Team

Find the probability of two independent events: both, either, neither and exactly one.

100% free No signup Works in your browser

1. What is the Probability Calculator?

For two independent events A and B, see the chance that both happen, at least one happens, neither happens, or exactly one happens. Enter probabilities as decimals (0.25) or percentages (25).

2. How to use the Probability Calculator

Here is the whole process, step by step. It takes less than a minute from opening the tool to seeing your result.

1Fill in the P(A) (0–1 or %), P(B) (0–1 or %) fields.
2Your result updates as you type — read it below the fields, with its breakdown where shown.

Your result updates as you type — there is nothing to press and nothing to wait for.

Everything runs in your browser — your files and text never leave your device.

3. Tips for best results

Your text never leaves your device — The tool runs entirely in your browser using JavaScript. Nothing is uploaded, so you can paste private documents without worry. That also means there is no account to create and no file to upload.
It works on your phone too — Open the tool in any modern browser on Android or iPhone. The layout adjusts to the screen and everything works the same way on a small screen as on a desktop.
Read the breakdown, not just the headline number — The result updates as you type. The breakdown underneath shows how the number was worked out, which is where mistakes usually show up.