Drop Rate / Dry Calculator
Enter a drop rate and kill count to see your odds -- pure probability math, no game data required.
For the third row below.
Chance of 0 drops in 400 kills
45.75%
Chance of at least 1 drop
54.25%
Expected kills for a drop
512
1 / drop chance
Kills for 50% chance
355
Kills for 90% chance
1,178
Kills for 75% chance
710
How it's calculated
chance of 0 drops in n kills = (1 − p)^n
chance of at least 1 drop = 1 − (1 − p)^n
kills for a target chance = ceil( ln(1 − target) / ln(1 − p) )
Worked example
A 1/512 drop rate after 400 kills:
| Chance of 0 drops in 400 kills | 45.75% |
| Chance of at least 1 drop | 54.25% |
| Kills for a 50% chance (median) | 355 |
| Kills for a 90% chance | 1,178 |
Frequently Asked Questions
What's the math behind a dry streak?
Each kill is an independent trial with the same drop chance p, so the probability of getting zero drops in n kills is (1 - p)^n -- multiply the "no drop" probability by itself once per kill. The chance of at least one drop is just 1 minus that. This assumes p never changes between kills; it doesn't apply to mechanics with a rising drop-rate floor.
How are "kills for 50% chance" and "kills for 90% chance" calculated?
Solving 1 - (1-p)^n >= target for n gives n = ceil( ln(1 - target) / ln(1 - p) ). Kills for a 50% chance is sometimes called the drop's "median" -- half of players will have received it by that point, half won't have, which is a different (and usually lower) number than the average (expected) kill count of 1/p.
Why is "expected kills for a drop" different from "kills for 50% chance"?
The expected (average) number of kills to first success for an independent-trial process is 1/p -- but because the underlying distribution is skewed (a small chance of a very long streak pulls the average up), the median (kills for a 50% chance) is meaningfully lower than the mean. Both numbers are real and correct; they just answer different questions.
Does a "dry streak" mean the game is due to give a drop?
No -- each kill is independent of the last under the standard model this calculator uses, so a long dry streak doesn't raise your odds on the very next kill (no "gambler's fallacy" correction happens automatically). It does mean, looking backward, that you landed in the less common tail of the distribution.
Max Hit Calc is a set of fan-made calculators built from the game's published combat and experience formulas, not affiliated with, endorsed by, or operated on behalf of Jagex Ltd. Old School RuneScape is a trademark of Jagex Ltd. Any preset gear, monster or action values above are typed from general knowledge of the game and are approximate -- verify the current figure in-game before relying on it. See the Terms.