Probability Calculator
Calculate probability for single events, combined AND/OR events, and complementary events. Results shown as decimal, percentage, odds, and fraction.
Enter values and click Calculate Probability to see results
Formula
What is Probability?
Probability measures the likelihood of an event occurring. It is a value between 0 (impossible) and 1 (certain).
Combined Events
AND (Intersection): The probability that both events occur. For independent events:
OR (Union): The probability that at least one event occurs:
Not Exclusive: P(A ∪ B) = P(A) + P(B) − P(A) × P(B)
Complementary Probability
The complement of an event A is the probability that A does not occur:
Related Tools
For counting arrangements, use our Permutation & Combination Calculator. For statistical analysis, try the Standard Deviation Calculator.
Frequently Asked Questions
What is the probability formula?
Probability = Favourable Outcomes ÷ Total Outcomes. The value ranges from 0 (impossible) to 1 (certain). Multiply by 100 to express as a percentage.
Is this calculator free, and do I need to sign up?
Yes, it is completely free with no sign-up. There are no usage limits and no paywalls.
Are my inputs saved or sent to any server?
No. Every calculation happens entirely in your browser. Nothing you type is uploaded, logged, or shared with us or any third party.