Expected Attempts Calculator
Enter a per-attempt drop chance and get the average number of tries it takes to land the drop — the reciprocal of the rate, with the variance you should still expect around it.
One number, instantly
Enter the drop chance per attempt as a percentage and the calculator returns the average number of attempts to get one drop (1 ÷ p).
It is an average
The result is an expected value across many runs, not a promise — luck means you may need far more or far fewer tries than this figure.
What is the expected number of attempts?
The average tries per drop
The expected attempts calculator turns a single number — the chance of getting a drop on each attempt — into the average number of tries it takes to land that drop. Any farmable item, gacha pull, or rare enemy spawn has a drop rate, and the smaller that rate, the more attempts you should plan for. The maths is simple: take the chance as a fraction and flip it. A 2% drop becomes one attempt in fifty, so fifty attempts is the average. It is the figure behind every "how many runs until I get it" question, and it sets a realistic expectation before you start grinding.
Enter a drop chance per attempt as a percentage to get the average number of attempts to land the drop instantly.
The expected number of attempts is one divided by the drop probability, where the probability is the percentage drop rate divided by 100.
expected attempts = 1 ÷ pThe drop rate is a percentage, so first convert it to a fraction by dividing by 100: a 2% chance becomes 0.02. Then take the reciprocal — one divided by 0.02 — to get 50. This is the mean of the geometric distribution, the standard model for the number of independent tries until the first success. Smaller chances flip into bigger averages: a 0.1% drop averages 1,000 attempts.
Suppose a rare item has a 2% chance to drop on each kill.
Convert the rate to a fraction
2% ÷ 100 = 0.02 — the per-attempt probability as a decimal.
Take the reciprocal
1 ÷ 0.02 = 50 — flipping the probability gives the average number of tries.
Read the result
50 attempts on average. Plan for around fifty kills, knowing some players finish much sooner and some much later.
The key thing to understand is that 50 attempts is an average, not a target you are guaranteed to hit. Across thousands of players farming the same 2% drop, the tries needed average out to fifty, but any individual run varies wildly: some land it on the first kill, others push well past a hundred. A useful rule is that after a number of attempts equal to the average, you have only about a 63% chance of having seen at least one drop — so roughly one player in three reaches fifty kills with nothing to show, which is ordinary variance rather than a bug or bad luck alone. Treat the number as a planning anchor: it tells you the scale of the grind and lets you compare two drops sensibly (a 2% drop averages 50 tries, a 1% drop averages 100, so the 1% item is twice the grind), but it never promises the drop will arrive on schedule.
The formula is exact for a fixed, independent chance, but a couple of practical points are worth keeping in mind.
Independent attempts and a fixed rate
This calculator assumes every attempt is independent and the drop chance never changes. Many games break that assumption with pity systems or guaranteed drops after a threshold, which lower the real number of attempts — in those games the figure here is a conservative upper estimate. It also gives the average, not a ceiling: there is no number of attempts that guarantees the drop when the rate is fixed.