Drop Rate Calculator
Each try is independent: at a drop rate of 1 in 128, even 128 tries give only a 63.4% chance of at least one drop, not 100%. The tool also finds the tries needed for a 50% or 90% chance.
How to use
- Enter the drop rate as a percentage, or switch the unit to 1 in N, for example 1 in 128.
- Enter how many tries you have made or plan to make. The chance of at least one drop appears at once.
- Set a target chance such as 90 to see how many tries you need. Raise the copies field if you need more than one drop.
How it works
Each try is independent. The chance of at least one drop in n tries is 1 − (1 − p)ⁿ, where p is the drop rate as a fraction. For 1 in 128 and 128 tries this gives 63.4%, not 100%.
The tries needed for a target chance t are n ≥ ln(1 − t) ÷ ln(1 − p), rounded up. For several copies the calculator adds up the exact binomial probabilities, so the answer is not an approximation.
Expected tries = copies ÷ p. It is an average. The luck of any single player can be far better or worse, which is why the target-chance row is the more useful number.
Past tries do not change the odds of the next one. The calculator tells you the odds before you start, not whether a drop is overdue.
FAQ
If an item drops 1 in 100, is it certain after 100 kills?
No. The chance is 63.4%. You are still empty-handed after 100 kills 36.6% of the time. Reaching 95% takes 299 kills.
How many tries for a 90% chance at a 0.5% drop?
You need 460 tries. The average is 200 tries, but about one player in ten still has nothing after 460.
How do I enter a rate like 1/512?
Switch the unit to 1 in N and type 512. The calculator converts it to 0.1953%.
Does the calculator handle guaranteed drops or pity?
No, it assumes a fixed rate for every try. For games with rising odds or a guaranteed pull, use the gacha pity calculator.