How to use this probability calculator
Enter the values requested above and select Calculate. Change any input to compare another scenario. The calculation runs locally in your browser and does not require an account.
Formula and method
Example
If A has probability 0.5 and B has probability 0.25, independent P(A and B) is 0.125.
Tips for a useful result
The combined-event results assume A and B are independent.
What this calculator is useful for
Calculate the probability of one event, its complement, and simple independent AND/OR combinations. The result is intended for quick estimates, checking arithmetic and comparing scenarios. When a result affects a contract, tax filing, medical decision, building-code requirement or other high-stakes situation, verify the result with the appropriate professional or authoritative source.
Frequently asked questions
What does the Probability Calculator calculate?
Calculate the probability of one event, its complement, and simple independent AND/OR combinations.
How does the Probability Calculator work?
For independent events, P(A and B) = P(A)×P(B). P(A or B) = P(A)+P(B)−P(A)P(B).
Is the Probability Calculator free to use?
Yes. ERICH Calculators is free to use and does not require an account.