Skip to content
HARESEL

Repeated Success Probability Calculator

Enter the success chance for one attempt and the number of independent attempts to see the combined probability instantly.

Calculate your probability

Results update as you type. Your inputs are also saved in the page URL for sharing.

Enter a value from 0 to 100. Decimals are allowed.

Enter a whole number of 1 or more.

Chance of at least one success
63.4%
Chance all attempts fail
36.6%
Expected successes
1

Attempts needed for a target chance

Minimum attempts needed to reach or exceed each chance of at least one success.

50%
69
90%
230
95%
299
99%
459

How this calculator works

What it calculates

It combines the same success chance across repeated attempts and also shows the average number of successes you can expect.

At least one success

The formula is 1 − (1 − p)ⁿ, where p is the success probability per attempt and n is the number of attempts.

Example

With a 1% chance per attempt over 100 attempts, the chance of at least one success is about 63.4%, not 100%.

Independent attempts

The calculation assumes each attempt is independent and has the same success probability. Pity systems or changing odds require a different model.