Math Calculators
Drop rate calculator: chance of at least one drop.
Enter a 1-in-N drop rate and how many tries you have made. See the odds of at least one drop, and how many tries it takes to reach 50%, 90%, 95% and 99%.
Inputs
Result
Enter a drop rate and a number of tries.
Assumes every try has the same fixed, independent chance. Pity counters, guaranteed drops and rates that change per try are not modelled. Use the rate your game or source publishes.
How the drop chance is calculated
If each try has a 1-in-N chance p = 1/N, the chance of at least one drop in n tries is 1 - (1 - p)n. That is the cumulative distribution of the geometric distribution, and its mean, the expected number of tries to the first drop, is 1/p = N. Note that after N tries your chance is only about 63%, not 100%.
To find the tries needed for a confidence level c (0.5, 0.9, 0.95, 0.99), solve 1 - (1 - p)n ≥ c, which gives n = ceil(ln(1 - c) / ln(1 - p)). For more than one drop, the chance of at least k drops is one minus the sum of the binomial probabilities of 0 to k-1 drops, where the chance of exactly x drops is C(n, x) px (1 - p)n-x.
This tool ships no game's drop rates. Type in the rate your game publishes, and remember that results describe odds over many players, not a promise for your next try.
Sources: Wikipedia, Geometric distribution; NIST/SEMATECH e-Handbook of Statistical Methods, Binomial distribution. Read 2026-09-29.