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Loot Drop Probability Calculator

Work out loot drop probability instantly with clear inputs, formula shown and shareable results.

About Loot Drop Probability Calculator

Independent attempts follow the geometric distribution: the chance of no drop is (1 - rate) to the power of attempts, and the attempts for a 90% chance is log(0.1) over log(1 - rate). At a 2% rate the average is 50 attempts but 115 are needed for a 90% chance, which is why runs of bad luck feel far worse than the headline rate suggests.

Formulas

At least one drop

P = 1 - (1 - drop rate) ^ attempts

Attempts for 90%

attempts = ln(0.1) / ln(1 - drop rate)

Worked example

With the default values below, Loot Drop Probability Calculator returns Chance of at least one drop of 86.7380%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Drop rate per attemptaccepts 0–100 %
2 %
Attempts mademinimum 1
100

Results

Chance of at least one drop
86.7380%
Drops expected
2.000
Attempts for a 90% chance
114
Average attempts per drop
50.00

Step by step

  1. 1Values used
  2. 2At least one drop
  3. 3Attempts for 90%
  4. 4Chance of at least one drop= 86.7380
  5. 5Drops expected= 2.000
  6. 6Attempts for a 90% chance= 114
  7. 7Average attempts per drop= 50.00

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Loot Drop Probability figure worked out?

P = 1 - (1 - drop rate) ^ attempts. Independent attempts follow the geometric distribution: the chance of no drop is (1 - rate) to the power of attempts, and the attempts for a 90% chance is log(0.1) over log(1 - rate).

Why does this matter?

At a 2% rate the average is 50 attempts but 115 are needed for a 90% chance, which is why runs of bad luck feel far worse than the headline rate suggests.

What do I need to enter?

Enter drop rate per attempt, attempts made. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

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