Steal an Egg Hatch Calculator
Plan hatch and mutation odds before you spend a single egg.
By Steal an Egg Wiki Team
Last updated:
Hatch & Mutation Odds Calculator
What “2% per hatch” actually means once you hatch 25 eggs — and how many you really need.
Reaching Speed 150 doubles the base mutation chance — roughly 2% to 4% per hatch.
Hatches needed for a realistic shot
17
50% chance
57
90% chance
113
99% chance
Formula: chance of at least one success = 1 − (1 − p)n, where p is the per-hatch rate and n is the number of hatches. The maths is exact; the default rates are community-observed, not published by the developer.
Why plan your hatches?
A “2% chance” feels hopeless until you run it 25 times. Hatching is a sequence of independent rolls, so the odds compound:
At p = 2% over 25 hatches that is roughly a 40% chance of at least one mutation; push your Speed to 150 and the rate doubles to 4%, turning those same 25 hatches into a 64% chance. That is the real value of the Speed 150 milestone.
For mutation multipliers and how they stack on pet income, see the Mutations guide, and for the pets those eggs produce, the Pet Tier List. The full suite of tools lives on the Calculators page.
Frequently Asked Questions
How do I use the hatch calculator?
Enter the per-egg success rate (for example a 2% or 4% mutation chance) and the number of eggs you plan to hatch. The tool shows your chance of at least one success and the expected number of successes.
What mutation rates should I use?
The developer does not publish official odds. Community observation puts the base mutation chance near 2% per hatch, doubling to about 4% once your Speed reaches 150. The calculator lets you type in any rate you prefer.
How many eggs for a guaranteed mutation?
Nothing is ever guaranteed in a roll-based system, but at 4% you need about 17 hatches for a 50% chance, 57 for 90%, and 113 for 99%. Use the calculator to model any rate and target.