Probability Calculator
Free probability calculator — single-event probability and combined odds of two independent events (and, or, neither).
Everyday Uses
Games & dice
Find the odds of a roll, draw, or coin flip.
Stats homework
Compute single and combined event probabilities.
Risk & chance
Understand "at least one" and "neither" outcomes.
Decisions
Turn favorable-vs-total counts into clear percentages.
Frequently Asked Questions
How do you calculate probability?
The probability of an event is the number of favorable outcomes divided by the total number of equally likely outcomes. Rolling a 6 on a die is 1 favorable ÷ 6 total = 0.167, or about 16.7%. Probability always falls between 0 (impossible) and 1 (certain).
How do you find the probability of two events?
For independent events, the chance of both A and B happening is P(A) × P(B). The chance of either one is P(A) + P(B) − P(A)×P(B). For two coin flips landing heads, "both" is 0.5 × 0.5 = 0.25, and "at least one" is 1 − 0.5 × 0.5 = 0.75.
What is the difference between odds and probability?
Probability compares favorable outcomes to the total, while odds compare favorable to unfavorable. A 1-in-6 dice roll is a probability of 1/6 ≈ 16.7%, but the odds are 1 : 5 (one way to win, five ways to lose).