Drop Chance Calculator

How this is calculated

Each attempt is independent, so the chance of getting NOTHING in a run of attempts is the chance of missing once, multiplied by itself for every attempt: (1 - p) to the power of n. The chance of at least one drop is everything else, so 1 minus that. That is the whole calculation, and it is the same in every game with a fixed drop rate. The rate is the only game-specific number, and you supply it. The attempts-for-50% and attempts-for-90% figures invert the same equation with a logarithm: how many attempts before the chance of still having nothing falls to a half, or to a tenth. The expected drops figure is simply rate times attempts. It is an average over many players, not a promise: at a 5 percent rate over 50 kills the average is 2.5 drops, and getting zero is perfectly ordinary. This assumes a fixed, independent rate. It does NOT apply to pity systems, bad-luck protection, guaranteed drops after N attempts, or loot tables that change with progress - those deliberately break independence.

Common questions

A 1 in 100 drop — am I guaranteed it in 100 tries?

No, and this is the most common misunderstanding about drop rates. In 100 attempts at 1 percent your chance of at least one is about 63 percent, not 100. Roughly a third of players will still have nothing, and that is the maths working correctly rather than bad luck.

Why is my expected drops number not a whole number?

Because it is an average across everyone doing the same grind. At 5 percent over 50 kills the average is 2.5 drops. No single player gets 2.5 of anything - some get 0, some get 5.

I am past the 90% point and still have nothing. Is something wrong?

Probably not. Ninety percent means one player in ten is still empty-handed at that point, and someone has to be that player. It only starts to suggest a wrong rate, or a drop you are not actually eligible for, when the still-having-none figure gets genuinely tiny.

Does this work for gacha pulls and pity systems?

For a plain rate with no pity, yes - this is the right tool. For pity, no, and you want the gacha pity calculator instead. Pity deliberately breaks the independence this maths assumes: a drop is guaranteed after a set number of pulls, and many games also raise the rate as you approach that cap. Once a counter is involved these numbers become a floor rather than the real odds, and the CAP usually decides the answer long before the probability does - at a 0.6 percent rate the raw arithmetic implies about 167 pulls, while a hard pity of 90 makes 90 the maximum. That is a different question, so it has its own tool.

Does the game remember my previous attempts?

In a fixed-rate system, no. Every attempt rolls fresh, and the 200 kills behind you change nothing about the next one. That is exactly why long dry streaks happen and why they are not evidence of anything.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Drop Chance Calculator at https://www.bfcbrilliance.com/tools/drop-chance-calculator.

What I entered:
- Drop chance (%): ___
- Attempts so far (tries): ___

What it calculated:
- Chance of at least one by now: ___
- Chance of still having none: ___
- Drops expected on average: ___
- Attempts for a 50% chance: ___
- Attempts for a 90% chance: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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