Loot tables in games such as RuneScape, World of Warcraft, Diablo, Minecraft or Genshin Impact give rare items a fixed chance per attempt. A common mistake is to think that a 1% drop arrives within 100 tries. It does not: each attempt is independent, so after 100 kills the chance of having seen the item at least once is 1 − 0.99¹⁰⁰ ≈ 63.4%, and about one player in three is still empty-handed.
Enter the drop rate in whichever form the game or wiki uses – a percentage, “1 in 512” or a decimal – and the number of attempts. The calculator returns the chance of at least one drop, of none (the “dry streak” probability), of at least k drops if you need several, and the expected number of drops. It also works backwards: how many attempts give a 50%, 90% or 99% chance, or any target you choose.
The results assume a constant drop rate with no pity timer or bad-luck protection. Games that guarantee a drop after a set number of failures, or raise the chance with each miss, will do better than these numbers.
How to use the Drop Chance Calculator
- Drop rate given as
- Drop chance
- Drop chance: 1 in
- Drop chance (decimal)
- Number of attempts (kills, runs, rolls)
- Number of drops you need
- Target probability
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Convert the rate to a probability p. The chance of missing every time is (1 − p)ⁿ, so at least one drop is the complement. Solving 1 − (1 − p)ⁿ = T for n gives the attempts needed. Several drops use the binomial distribution.
Worked example
A boss drops a pet 1 time in 100 (p = 0.01). After 100 kills: 1 − 0.99¹⁰⁰ = 1 − 0.366 = 63.4%. For a 90% chance: ln(0.1) ÷ ln(0.99) = 229.1, so 230 kills; for 99%: 459 kills. A 3/100 drop gives 1 − 0.97¹⁰ ≈ 26.3% in 10 rolls and 1 − 0.97¹⁰⁰ ≈ 95.2% in 100.
Chance of at least one drop after n = X attempts
| Attempts | Chance |
|---|---|
| 0.5 × X | 39.3% |
| 1 × X | 63.2% |
| 2 × X | 86.5% |
| 3 × X | 95.0% |
| 4.6 × X | 99.0% |
Inputs explained
| Field | What to enter |
|---|---|
| Drop rate given as | Choose one: Percentage, 1 in X, Decimal (0–1) |
| Drop chance | In % |
| Drop chance: 1 in | A number |
| Drop chance (decimal) | A number |
| Number of attempts (kills, runs, rolls) | A number |
| Number of drops you need | A number |
| Target probability | In % |
What each result means
- Chance of at least one drop = (1 – (1 – [p])^[Number of attempts (kills, runs, rolls)])×100
- Chance of no drop at all = ((1 – [p])^[Number of attempts (kills, runs, rolls)])×100
- Expected number of drops = [Number of attempts (kills, runs, rolls)]×[p]
- Average attempts per drop = 1÷[p]
- Chance per attempt = ([p])×100
Formula
P(at least one) = 1 − (1 − p)ⁿ · attempts for target T: n = ⌈ln(1 − T) ÷ ln(1 − p)⌉ · expected drops = n × p · P(at least k) = 1 − Σ₀ᵏ⁻¹ C(n, i) pⁱ(1 − p)ⁿ⁻ⁱ
Worked example
Inputs — Drop rate given as: 1 in X; Drop chance: 1 in: 100; Number of attempts (kills, runs, rolls): 100; Number of drops you need: 1; Target probability: 90 %.
Results — Chance of at least one drop = 63.4 %; Chance of no drop at all = 36.6 %; Chance of at least k drops = 63.4 %; Expected number of drops = 1; Average attempts per drop = 100; Attempts for the target probability = 230; Attempts for a 50% chance = 69; Attempts for a 90% chance = 230; Attempts for a 99% chance = 459; Chance per attempt = 1 %.
Key terms
- Drop rate
- Probability that one attempt gives the item.
- Independent event
- An attempt whose outcome does not depend on earlier ones.
- Dry streak
- A long run of attempts without the drop.
- Pity system
- A game rule that guarantees or boosts a drop after many failures.
Frequently asked questions
Does a 1% drop rate mean I get it in 100 tries?
No – after 100 tries the chance is 1 − 0.99¹⁰⁰ ≈ 63.4%. You need 230 tries for 90% and 459 for 99%.
How do I calculate the chance of getting an item at least once?
1 − (1 − p)ⁿ, where p is the drop rate and n the number of attempts.
What are the odds of a 1/512 drop in 512 kills?
1 − (511/512)⁵¹² ≈ 63.2% – the same 63% you get whenever attempts equal the "1 in X" number.
What is a dry streak?
Going far beyond the drop rate without the item. The chance of being 3× the rate dry is about e⁻³ ≈ 5%.
Do my previous failures make the next drop more likely?
Not unless the game has a pity system; each roll is independent.
How many kills for two drops of a 1/100 item?
About 168 kills give a 50% chance of at least two; the average is 200.
What is the average number of attempts?
1 ÷ p – 100 for a 1% drop – but half of players get it sooner than 69 attempts.