Probability Calculator
Calculate single event, AND, and OR probabilities. Results shown as fraction, decimal, and percent.
Example: rolling a 4 or higher on a 6-sided die = 3 favorable / 6 total
P(Event)
50.00%
Formula: 3 / 6
Probability Bar
Statistics & Probability Guide
Free probability cheat sheet and worked examples.
Frequently Asked Questions
How is basic probability calculated?
Probability = number of favorable outcomes / total number of possible outcomes. The result is always between 0 (impossible) and 1 (certain).
What is the difference between AND and OR probability?
P(A AND B) = P(A) × P(B) for independent events — both events must occur. P(A OR B) = P(A) + P(B) − P(A AND B) — at least one event occurs. The subtraction prevents double-counting overlapping outcomes.
What does independent probability mean?
Two events are independent if the outcome of one does not affect the other. For example, flipping a coin twice: the first flip has no effect on the second. The AND formula P(A)×P(B) only applies to independent events.