Probability Calculator

How to use Probability Calculator

1. Open Probability Calculator in your browser — it loads instantly and works offline once cached.
2. Enter your values in the input fields. Every field is labelled so you know exactly what to type.
3. The result updates automatically as you type — there is no "submit" round-trip to a server.
4. Adjust any input to compare scenarios and see how the outcome changes in real time.
5. Copy or note the result. Nothing you enter is stored or sent anywhere.

Why use Probability Calculator?

• 100% free with no limits, no sign-up and no watermarks.
• Private by design — your data are processed in your browser and never uploaded to a server.
• Fast and lightweight, with instant results even on a phone or a slow connection.
• Works everywhere — any modern browser on Windows, macOS, Linux, Android or iOS.
• Part of a full math calculators suite, so related probability tasks are one click away.

What people use Probability Calculator for

• Calculating the probability of combined or sequential events.
• Working out combinations and permutations.
• Checking a homework answer on dice, cards or coins.

Probability Calculator: limits and things worth knowing

• Independent events multiply: two fair coins both landing heads is 0.5 × 0.5 = 0.25. Events are only independent if one genuinely does not affect the other.
• The complement is often far easier: the probability of at least one success is 1 minus the probability of none.
• Order matters for permutations and not for combinations. nCr = n! ÷ (r!(n−r)!) counts selections; nPr counts arrangements.
• The gambler's fallacy is the belief that past independent results affect future ones. A fair coin after ten heads is still 50/50.

Is it private and secure?

Your privacy is built in. Probability Calculator runs completely on your device, so whatever you enter stays in your browser and is never transmitted, logged or stored on any server.

Network activity: none. Nothing is sent and nothing is fetched. This tool makes no network request at all once the page has loaded — which is why it keeps working if your connection drops.

You do not have to take that on trust — our privacy proof page publishes the Content-Security-Policy that enforces it, lists every third party it permits, and shows how to verify the whole claim yourself.

Learn more

Why Browser-Based Tools Are Safer for Your Files — Most online converters upload your files to a server. Client-side tools don't. Here's why that difference matters for privacy.