Probability Calculator
Enter the probabilities of two independent events to see the chance of both, either or neither happening.
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The rules used
- A and B (both): P(A) × P(B), for independent events.
- A or B (at least one): P(A) + P(B) − P(A) × P(B).
- Not A: 1 − P(A).
- At least once in n tries: 1 − (1 − P(A))ⁿ. With a 1-in-6 chance per roll, the chance of at least one six in 4 rolls is 1 − (5/6)⁴ ≈ 51.8%.
Independent events
These formulas assume the events don't affect each other, like two coin tosses or two dice. If one event changes the chance of the other (drawing cards without putting them back, or rain and traffic jams), the results won't be exact. Those need conditional probability.
Odds
Odds compare the chance of not happening with happening. A probability of 20% is odds of 1 : 4. Enter probabilities as percentages: 0.5 as a fraction is 50%.
Free to useNo software to install — works in any modern browser.
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Runs in your browserNothing you enter is sent to a server.
Works on mobileSame tool on your phone, tablet or desktop.
How it works
- Enter — type or paste your values or text.
- Get the result — it is worked out in your browser.
- Adjust — change the inputs to compare, or copy the result.
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