“At Least Once” Probability Calculator
A 1-in-37 shot, tried 37 times, is not a sure thing — it misses completely about 36% of the time. Find the real odds for any repeated chance.
Your chance
Presets:
—At least once
—Never
—Expected hits
Tries needed for…
Chance of at least one hit vs. tries
The formula
P(at least one success in N tries) = 1 − (1 − p)^N
Tries needed for target T: N = ln(1 − T) ÷ ln(1 − p)
Notice what happens when N equals the “1 in X” figure: the answer is always close to 63%, because (1 − 1/N)^N approaches 1/e ≈ 36.8% as N grows. That constant is part of why we're called e.casino — see the about page. For streaks and the illusion of “due” outcomes, try the Coin-Flip Lab and read The Gambler's Fallacy.