OSRS Pet Drop Rates and Dry Chance

Use the calculator first

Open the OSRS Pet Chance Calculator and replace the example defaults with values for the exact OSRS activity you are modeling.

Formula and assumptions

Single-roll probability is 1 divided by the drop-rate denominator. Cumulative chance after n independent attempts is 1 minus (1 minus p) raised to n. Dry chance is the complement. Attempts for a target probability use the logarithmic inverse of the cumulative formula and are rounded up.

Worked example

For a 1 in 5,000 pet chance per eligible roll, 5,000 independent attempts do not guarantee the pet. The cumulative probability is about 63.2%, while the dry probability remains about 36.8%.

Visual explanation

The calculator includes a live result diagram and a calculation-flow diagram. They use the same inputs and outputs as the calculator rather than a separate hidden model.

Important limitations

This model assumes independent eligible rolls with a constant probability. Some OSRS pets use activity-specific formulas, scaling, thresholds, experience-based rates, kill-count modifiers, or other mechanics that cannot be represented by a single fixed 1-in-N rate. Verify the exact pet formula before using the calculator.

Source

Verify method-specific values against current Old School RuneScape information before using a large cost, training, or probability plan.