Probability Calculator

Calculate basic probability of single and compound events.

Probability Calculations

Select mode and enter probabilities

Calculation Mode

Favorable Outcomes

Total Outcomes

P(A)

P(B)

Event Relationship

P(B|A) — Probability of B given A

P(A)

P(B)

P(A ∩ B) — Both events occurring

P(A)

Enter your values above and tap Calculate Probability to see the result.

Your Results

Probability

Select a mode and enter values above, then tap Calculate.

Step-by-step Solution

Probability Formulas

Basic:
P(A) = Favorable / Total

AND (indep):
P(A∩B) = P(A) × P(B)

AND (dep):
P(A∩B) = P(A) × P(B|A)

OR:
P(A∪B) = P(A) + P(B) − P(A∩B)

Complement:
P(A') = 1 − P(A)

Related Calculators

Binomial Distribution

Statistics

Combination Calculator

Mathematics

Normal Distribution

Statistics

Key Concepts

Mutually Exclusive: Two events that cannot occur simultaneously. If A and B are mutually exclusive, P(A∩B) = 0.

Independent Events: The occurrence of one event does not affect the probability of the other. P(B|A) = P(B).

Dependent Events: The outcome of one event affects the probability of another. Use conditional probability P(B|A).

Complement Rule: The probability that an event does NOT occur is 1 minus the probability it does occur.

Pro Tips

Results update as you type — change any field to see the effect immediately.

Check that every value uses the same unit before comparing results.

Use the copy button to paste the probability figures into a note or spreadsheet.

Nothing is sent to a server, so you can use this with private figures.