Mutation breeding is a numbers game. Pick the stat you want to mutate, configure the traits on both parents, and this tool tells you how many females per round you need to reliably hit that mutation.
+0% per-roll mutation chance+0 target stat weight+0% higher stat inheritance
Breeding pool size
23420% failure rate1 in 5 rounds fail
33510% failure rate1 in 10 rounds fail
4365% failure rate1 in 20 rounds fail
5692% failure rate1 in 50 rounds fail
Breeding group size
Success rate: 0.6859% (1 in 146 rounds)Failure rate: 99.31%
How mutation chance is calculated
Every breeding pair gets three mutation rolls by default. Each roll has a 2.5% base chance to trigger a mutation, and if it triggers it picks one of the mutable stats uniformly. If the chosen stat is the one you want, there's still a 55% base chance the offspring inherits the higher parent's value, which is required for the mutation to be useful.
ASA traits stack on top of this. Mutable traits add to both the per-roll chance and the stat-pick weight. Robust traits add to the 55% inheritance chance. Frail traits subtract from it. The calculator multiplies these together per roll, combines across three rolls, and finally accounts for gender (50% if you only accept males).
The number of females you need is the smallest count such that no single female succeeding is rarer than your chosen failure tolerance. Mathematically that's the ceiling of log(accept) / log(fail-per-female).
Frequently Asked Questions
How many females do I need for a mutation?⌄
Practical breeding lines use 10-20 mutator females per generation. More females improves the chance of rolling a desirable mutation per breeding cycle.
What do Mutable, Robust and Frail traits do?⌄
Mutable boosts mutation odds, Robust grants extra hit points, and Frail reduces stamina drain. Each trait shifts the probability distribution of inherited stats.
Does off-stat Mutable help or hurt?⌄
Off-stat Mutable increases mutation chance on stats you don't care about, which dilutes your line. Pair with stat-locked breeding to keep mutations focused on the target stat.
What happens if one parent is mutation capped?⌄
If both parents are over the 20-mutation cap, no new mutations roll. Pair a low-mutation parent with the capped parent to keep the chance alive.
Does this calculator work for the S+ Mutator?⌄
Yes - the calculator supports stock vanilla rules and the S+ Mutator workflow. Switch the toggle above to match your server setup.