OSRS Drop Rate Calculator
Find at-least-one, dry, expected-drop and reverse kill-count probabilities.
See dry chance and reverse kill targets
36.7520% chance of receiving zero in 512 kills
OSRS Wiki drop-rate formula and individual drop tables · reviewed 2026-09-05. Probability is 1 − (1 − p)ⁿ. Independent drops have no memory unless Jagex documents a separate pity or threshold mechanic.
What the OSRS Drop Rate Calculator calculates
The OSRS Drop Rate Calculator answers two different loot questions: the chance of at least one success after a kill count, and the number of kills needed to reach a chosen cumulative chance. It accepts familiar inputs such as 1/128, 1/512, or 1/5000.
Expected drops are shown separately from probability. Reaching the denominator gives an expectation of one drop, but it does not create a guarantee; the at-least-one chance is only about 63.2 percent for a 1/n independent roll repeated n times.
Use the Drop Rate Calculator
- 1
Enter the exact per-kill rate from the monster’s current drop table.
- 2
Set completed or planned kills.
- 3
Read both success and zero-drop probabilities, then use reverse milestones for a goal.
A result you can audit
Each section documents the calculation and the limits that apply to this specific gameplay problem.
How This OSRS Drop Rate Calculator Works01+
For probability p and kills n, zero drops equals (1−p)^n. At least one is 1−(1−p)^n, expected drops are n×p, and the reverse target uses ceiling(log(1−target) ÷ log(1−p)).
Each kill is treated as independent. The previous dry streak does not raise the next ordinary roll unless Jagex documents a separate threshold, guaranteed drop, or bad-luck system.
Worked Example for the OSRS Drop Rate Calculator02+
At 1/512 over 512 kills, expected drops equal exactly one while the chance of at least one is about 63.248 percent. A 50 percent cumulative chance arrives at 355 kills, not 256 or 512.
How to Use the OSRS Drop Rate Calculator Result03+
Use the reverse rows to choose a probability tolerance. Ninety-five percent still leaves a five percent dry tail; do not convert a planning milestone into a promise about the next kill.
OSRS Drop Rate Calculator Accuracy and Limitations04+
Multi-roll tables, tertiary drops, conditional rolls, kill-count guarantees, team allocation, and changing rates need separate modeling. Presets are conveniences and should be checked against the linked monster page.
Independent OSRS drop outputs
Probability and expectation are deliberately shown as different concepts.
| Output | Formula | Interpretation |
|---|---|---|
| Zero drops | (1−p)^n | Dry chance |
| At least one | 1−(1−p)^n | Cumulative success |
| Expected drops | n×p | Long-run average |
| Reverse kills | log ratio, rounded up | Chance target |
Official references used for this page
OSRS calculator FAQs
Clear answers about calculations, data, independence, privacy and practical use.
Is an OSRS drop guaranteed at its denominator?
No. At n attempts for a 1/n independent drop, the at-least-one probability approaches 63.2%, not 100%.
What does being dry mean in the OSRS result?
The zero-drop percentage is the probability that every independent attempt so far failed.
How many OSRS kills give a 95% drop chance?
It depends on the entered rate; the reverse row solves and rounds the required kill count upward.
Does the OSRS drop tool handle guaranteed thresholds?
Not automatically. A documented guaranteed drop or pity mechanic must be modeled separately from independent probability.