XP Calcs
Independent drop probability

OSRS Dry Calculator

Enter a one-in-X drop rate and completed attempts to see the chance of at least one success, the probability of still being dry, and the median attempt count.

Enter the drop and attempts

Chance of at least one

63.40%

Chance of still being dry: 36.60%

50% chance reached by 69 attempts.

How it works

Every eligible attempt is treated as an independent Bernoulli trial with the same probability. The complement method is exact: it calculates the chance that every attempt fails, then subtracts that number from one. A listed drop rate is not a guarantee or a countdown.

P(at least one)=1−(1−1x)nP(dry)=(1−1x)n\begin{aligned} P(\text{at least one}) &= 1 - \left( 1 - \frac{1}{x} \right)^n \\ P(\text{dry}) &= \left( 1 - \frac{1}{x} \right)^n \end{aligned}
Inputs are kept at full precision. Discrete counts round up when a partial action cannot complete the goal; probabilities and rates keep their fractional meaning.

Worked example

At a 1 in 100 rate across 100 independent kills, the chance of at least one drop is about 63.40%; roughly 36.60% of players are still dry.

Interpreting the result

Start by checking that each field describes the same scenario as the result: levels are visible base levels, bonuses are entered separately, costs are per unit, and a one-in-X rate means one divided by X on each eligible roll. The calculator updates immediately and writes the complete input state into the address bar. “Copy link” preserves those assumptions; “Copy result” copies a short summary rather than the entire method.

Do not treat a rounded count as an hourly rate. A required-action total says how many successful units complete the target under the entered reward. Banking, movement, failed attempts, animation timing, missed ticks and setup changes affect elapsed time. When time matters, measure a representative session with the same method and divide the required count by the observed successful actions per hour.

Economic outputs are arithmetic scenarios rather than live market quotations. Check current item values before buying supplies, include any outputs that can be sold, and consider limits or low-volume price movement. Probability outputs describe repeated independent trials; they do not promise that a result arrives at the displayed attempt count. The visible formula is the authority for what this page includes.

Read this as a planning estimate. Game updates, equipment effects, failures, travel, downtime and live prices can move a real session away from the mathematical result. Check the inputs against the account and use the output as a reproducible baseline.

Questions about OSRS Dry Calculator

Am I guaranteed the drop at the denominator?
No. At x attempts for a 1/x drop, the success chance is about 63.2%, not 100%.
Does going dry improve the next roll?
Not for independent drops. The next eligible roll keeps the same probability unless the game has an explicit protection mechanic.
What does dry percentile mean?
The dry probability is the share of equivalent independent streaks expected to last at least this long without success.

Sources

Mechanics and fixed tables were reviewed in 2026. Price-like inputs are user-controlled or approximate rather than live quotes. Source links name the public reference used for the page; the visible formula states the exact implementation.

  1. Old School RuneScape Wiki — Experience — Public XP table and level formula, reviewed 2026.
  2. Old School RuneScape Wiki — Combat level — Seven-stat combat-level formula, reviewed 2026.
  3. Old School RuneScape Wiki — Maximum melee hit — Effective Strength and maximum-hit formula, reviewed 2026.
  4. Old School RuneScape Wiki — Attack roll — Accuracy and defence-roll mechanics, reviewed 2026.
  5. Old School RuneScape Wiki — Calculators — Public skill, activity and reward tables, reviewed 2026.

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