Probability Calculator

Combine the probabilities of two events: and, or, not, and at least one in several tries.

What Do You Want to Find?
Fractions and decimals both work.
–
Result
A and B
A or B (at least one)
Exactly one
Neither
Not A
Work

Saved Calculations

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Probability Rules

Independent: P(A and B) = P(A) × P(B)
P(A or B) = P(A) + P(B) − P(A and B)   P(not A) = 1 − P(A)
At least once in n tries = 1 − (1 − p)ⁿ

Worked Example

Tips

"Independent" means one event doesn’t change the other’s chance (separate coin flips). Drawing cards without replacement is not independent; use conditional probability for those.