Mathematical Tools

Probability Calculator

Calculate probability for single events, combined AND/OR events, and complementary events. Results shown as decimal, percentage, odds, and fraction.

✓ Runs in your browser · Updated 2026-03-31

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Calculate probability for single events, combined AND/OR events, and complementary events. Results shown as decimal, percentage, odds, and fraction.

Updated: 2026-03-31

What is Probability?

Probability measures the likelihood of an event occurring. It is a value between 0 (impossible) and 1 (certain).

P(Event) = Favorable Outcomes / Total Outcomes

AND (Intersection): The probability that both events occur. For independent events:

P(A ∩ B) = P(A) × P(B)

OR (Union): The probability that at least one event occurs:

Mutually Exclusive: P(A ∪ B) = P(A) + P(B)
Not Exclusive: P(A ∪ B) = P(A) + P(B) − P(A) × P(B)

The complement of an event A is the probability that A does not occur:

P(A') = 1 − P(A)

For counting arrangements, use our Permutation & Combination Calculator. For statistical analysis, try the Standard Deviation Calculator.

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.