Probability Calculator
Calculate the probability of a single event, or combine two independent events.
Reviewed by the WorldCalcs team · Methodology · Last reviewed: June 2026
Result
0.1667
= 16.67%
What is a probability calculator?
Probability measures how likely something is, from 0 (impossible) to 1 (certain). This calculator finds the probability of a single event, and combines two independent events to show the chance that both happen, that at least one happens, or that neither happens.
How it's calculated
For a single event, probability = favorable outcomes / total possible outcomes. For two independent events A and B (where one does not affect the other): both happen P(A and B) = P(A) × P(B); at least one happens P(A or B) = P(A) + P(B) − P(A) × P(B); neither happens = (1 − P(A)) × (1 − P(B)).
Example
Rolling a 4 on a die: 1 favorable / 6 total = 0.1667, or 16.67%. Flipping two coins (each heads = 0.5): both heads = 0.5 × 0.5 = 0.25; at least one head = 0.5 + 0.5 − 0.25 = 0.75; no heads = 0.5 × 0.5 = 0.25.
All calculations happen in your browser. Nothing is sent, stored, or tracked.
Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer
How to use
Choose Single event and enter favorable / total outcomes, or choose Two independent events and enter each probability (0–1, or with a % sign).
The two-event mode returns the AND, OR, neither, and exactly-one probabilities, assuming the events do not influence each other.