Steal an Egg Hatch Calculator
Plan hatch and mutation odds before you spend a single egg.
By Steal an Egg Wiki · Site Maintainer: CT
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.
Reading the output
Two different numbers come out of a hatch plan and people mix them up constantly. The chance of at least one answers “will this session give me anything?” and it rises steeply at first, then flattens. The expected number of successes answers “how much should I expect?” and it grows perfectly linearly — double the eggs, double the expected hits. If you are deciding whether a session is worth the time, use the first number. If you are budgeting eggs, use the second.
| Eggs hatched | At 2% (base) | At 4% (Speed 150) | Expected hits at 4% |
|---|---|---|---|
| 10 | ~18% | ~34% | 0.4 |
| 25 | ~40% | ~64% | 1.0 |
| 50 | ~64% | ~87% | 2.0 |
| 100 | ~87% | ~98% | 4.0 |
Where the base rate comes from
The developer does not publish official hatch or mutation odds, so the defaults in this tool are community-observed figures rather than developer-confirmed ones: a base mutation chance of roughly 2% per hatch, understood to double once your Speed reaches 150. That is exactly why the calculator takes your own input — if you have tracked your own session and your rate differs, use your number. The maths is exact; the default rate is an estimate, and the two should not be confused.
Three mistakes that waste eggs
- Reading a per-hatch chance as a session guarantee. “2%” does not mean one hit per 50 eggs; it means about a two-in-three chance of at least one across 50, and a real chance of none.
- Hatching before the Speed 150 milestone. If the double rate is right, every egg opened before that threshold costs you half its value in expected hits. Bank the eggs and push Speed first.
- Planning around a session instead of a target. Decide the outcome you want (a mutation, a specific tier), let the calculator tell you the egg volume, then work out whether your current Speed and income can fund that volume at all.
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.