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Real binomial math, no pity timer.
OSRS Drop Rate Calculator
A 1 in 512 drop does not mean one drop every 512 kills. Enter the rate and your kill count to see your real chance of seeing the drop, your odds of going dry, and how many kills it should take.
-Chance of at least one drop
-Chance of going dry
-Expected kills
-Median kills
The drop probability formula
Every kill in OSRS is an independent roll, so the chance of getting at least one drop in N kills at a 1-in-X rate is: P = 1 - (1 - 1/X)^N. There is no bad-luck protection in OSRS: going dry for twice the drop rate is always possible, and this calculator shows exactly how likely it is.
Expected kills vs. median kills
Expected kills (1/p) is the long-run average, but half of all players get the drop before the median, which is lower: ln(0.5) / ln(1 - p). For a 1/512 drop, the expected kills are 512 but the median is only about 355. If you are past the median with no drop, you are officially unlucky, not broken.
Worked example
A 1 in 512 drop over 1,000 kills: chance of at least one drop = 1 - (511/512)^1000 = 85.8%. Chance of going completely dry = 14.2%. Expected kills = 512, median = 355. About one player in seven walks away empty-handed after 1,000 kills.
From odds to profit
Knowing your drop odds is half the plan. Feed the same drop table into the OSRS GP per hour calculator to turn those chances into an expected hourly profit, and use the OSRS XP calculator to see how much XP the grind earns along the way.
Planning estimate only. Results use the list prices shown and may differ from your actual bill. Terms
Frequently asked questions
Can I really go 1,000 kills dry on a 1/512 drop?
Yes. About 14.2% of players go dry on a 1/512 drop over 1,000 kills. OSRS has no pity timer or bad-luck mitigation, so long dry streaks are a normal part of the math.
What is the difference between expected and median kills?
Expected kills (1/p) is the average over infinite attempts. The median is the point where half of players have the drop, and it is always lower. For planning, the median is the more useful number: you are more likely than not to be done by then.
Does going dry make the drop more likely?
Each kill rolls independently, so past kills never change the odds. A drop is never due. The calculator's dry-streak chance already accounts for this.
What if a drop comes from multiple sources?
Enter the combined rate. If a boss drops the item at 1/512 from two different mechanics, add the rates. If the wiki lists 2/512, simplify it to 1/256.