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Drop Rate Probability Calculator

See your odds over many runs.

Result

63.58%
1.00

How it is calculated

The tool finds the chance of getting at least one drop in a number of independent attempts. It first computes the chance of getting nothing every time, (1 − p/100)n, and subtracts it from 1: P = 100 × (1 − (1 − p/100)n). Here p is the drop rate as a percentage (2 for 2 %, not 0.02) and n the number of attempts, a whole number of at least 1. The drop rate must be above 0 and at most 100. It also shows the expected number of drops, n × p / 100. Every attempt is treated as separate with the same rate: pity counters, guaranteed drops and rate boosts are not modelled.

Worked example

A rare item drops at 2 % per kill and you farm 50 kills. The chance of no drop in one kill is 1 − 0.02 = 0.98. Over 50 kills that is 0.9850 ≈ 0.3642. Subtract from 1: 1 − 0.3642 = 0.6358. The calculator shows 63.58% and an expected 1.00 drops. So even after the number of kills that 'should' give one drop on average, you still miss about 36 % of the time.

Try this example →

Common mistakes

  • Multiplying: 2 % × 50 = 100 %. Chances do not add up like that. The real probability here is 63.58 %.
  • Typing the rate as a decimal. A 0.5 % drop must be entered as 0.5, not 0.005.
  • Assuming that the expected number of drops is a guarantee. An expected value of 1.00 still leaves a large chance of zero.
  • Expecting the odds to improve because you have failed so far. Each attempt is independent and the tool does not model pity systems.
  • Using the rate shown in a game for one item when the drop is a pool of several items, or confusing 'per kill' with 'per run'.

About this calculator

If a single attempt has a fixed drop chance p, the probability of getting at least one drop across n independent attempts is 1 − (1 − p)^n, not p × n as intuition often suggests — this is because the calculation works out the chance of getting nothing at all across every attempt, then subtracts that from 1, which correctly accounts for the fact that at least one success and all failures are complementary outcomes.

Gamers use this formula constantly to estimate their odds of getting a rare item drop, loot box pull, or gacha character over a given number of runs, pulls, or kills, and it’s the same math game designers use in reverse when balancing drop rates to hit a target average number of attempts before a player gets an item. It also explains why pity or guaranteed-drop systems exist in many games — without them, a low enough drop rate leaves a meaningful chance of going far longer than average without a single drop.

This calculator takes a drop rate and number of attempts and returns the probability of getting at least one drop.

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