At least once probability calculator
For example the chance of at least one six in 4 dice rolls, or how many tries give a 95% chance.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter chance per try, number of tries and target chance.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
P(at least once) = 1 - (1 - p)^n. Tries to reach target T = the smallest whole number ≥ ln(1 - T) ÷ ln(1 - p).
Example
Inputs: Chance per try = 10 %, Number of tries = 10, Target chance = 50 %. Result: Chance of at least once: 65.132156%; Chance it never happens: 34.867844%; Tries needed for the target: 7.
Limits and caveats
- Assumes independent tries with the same chance each time.
Questions about this tool
What is the chance of at least one six in 4 rolls?
1 - (5/6)^4 ≈ 51.77%, just over half.
Why is 10 tries at 10% not 100%?
Chances do not add up, since any try can fail; the right answer is about 65.1%.
Does a losing streak raise my chance next time?
No, with independent tries the chance stays the same every time.