OSRS Drop Chance Calculator
See the odds of any drop after your kill count; pick a preset boss rate or enter your own 1-in-N.
Popular uniques, rates from the official OSRS Wiki.
Example: 512 means a 1/512 drop. Decimals like 162.5 are fine.
How many kills you've done without the drop.
Your chance of the drop in your next N kills.
How to use the drop chance calculator
- Pick your drop from the preset list, or type its 1-in-N rate yourself.
- Enter how many kills you've done at that drop.
- Read your chance of having the drop by now, plus the odds on your next kills.
- Copy the result or a share link for your clan chat.
How it works
Every kill is an independent roll with a 1-in-N chance, so the probability of still being dry after K kills follows the binomial formula:
P(at least one drop) = 1 − (1 − 1/N)^K Worked example: a 1/512 unique after 500 kills gives 1 − (511/512)500 ≈ 62.4%. The chance you'd still be dry is the remaining 37.6%, which is completely normal. Even after exactly N kills (512 at 1/512), the chance is only about 63.2%, never 100%.
Preset rates were copied from the official OSRS Wiki on 2026-09-30. Sources and re-verification dates are listed on the methodology page.
What this calculator can't tell you
It models flat per-kill rates only. Some content uses different mechanics, for example, the Barrows chest scales with reward potential, and raids roll loot from points-based tables. For those, check the drop table on the OSRS Wiki. And remember: past kills never improve future odds. Every kill rolls the same 1-in-N.
Frequently asked questions
Does my chance of a drop go up the more kills I do?
Not on any single kill: each kill rolls the same 1-in-N chance independently. What grows is your cumulative probability: the chance you'll have seen at least one drop across all your kills.
Why isn't the chance 100% after exactly N kills?
Because the rolls don't remember each other. At 1/512, 512 kills gives roughly a 63.2% chance, and even 3,000 kills only reaches about 99.7%. There is no pity timer on a flat-rate drop.
What does a 1-in-512 drop rate actually mean?
Each kill independently has a 512-sided roll: one side drops the item, 511 don't. Over many players the average works out to one drop per 512 kills, but any single grind can land anywhere.
Can I use this for boss pets?
Yes, but the pet chance calculator already has every boss pet rate preset, so it's quicker.
Is the math exact?
Yes; it's the exact binomial probability, computed in your browser. The only way a result is wrong is if the drop rate itself changed, so preset rates carry a verification date. Tell us if you spot a stale one.
Related calculators
Built and maintained by the OSRSCalc founder · Drop rates verified against the official OSRS Wiki on 2026-09-30 · Page last updated 2026-09-30
See the formulas and methodology · Spotted a wrong rate? Tell us · Everything runs in your browser - nothing you enter leaves your device.