How does IV inheritance work in this model?

A fixed number of stats are guaranteed to copy one parent's IV exactly, chosen at random without repeats. The remaining stats roll a fresh random IV from 0 to 31. This matches the standard breeding inheritance system.

How is the chance of a perfect offspring computed?

For each target stat the tool checks whether at least one parent already has a perfect 31 in it. Inherited stats then need to land on a perfect parent slot, and any non-inherited target stat must roll 31 by chance, which is 1 in 32.

What does the expected attempts number mean?

It is one divided by the per-egg success probability — the average number of eggs to get one offspring meeting all your targets. The actual count varies because each egg is independent, but this is the long-run average.

Why do more guaranteed inherited stats help so much?

Each stat that must be rolled randomly only hits 31 one time in 32. Forcing five stats to inherit from perfect parents removes five of those long-shot rolls, cutting the expected attempts dramatically.

Does nature or gender affect the math here?

This tool focuses on IV inheritance probability. Nature and gender add independent multipliers you can layer on separately; the attempt count shown is for hitting your IV targets only.

Terraria Breeding & IV Calculator

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Breeding for perfect stats is a numbers game. This calculator models the standard IV inheritance system — a set number of guaranteed inherited stats plus random rolls for the rest — and tells you the real probability of a perfect offspring and how many attempts it should take.

How it works

The inheritance model assigns IVs to offspring in two ways. A fixed count of stats are forced to copy a parent’s exact IV, and the rest roll uniformly from 0 to 31. The chance any single random stat lands on a perfect 31 is 1/32. To meet all your targets, every target stat must either be a guaranteed-inherit slot that copies a perfect parent, or win the 1/32 random roll. Multiplying those independent probabilities gives the per-egg success chance, and:

expectedAttempts = 1 / successProbability

Tips and example

Suppose you want a perfect 31 in three stats, both parents already hold 31 in two of them, and five stats are guaranteed to inherit. The two covered targets are near-certain through inheritance, while the third must either inherit from a perfect parent or roll 31. Stacking perfect parents on the stats you care about is the single biggest lever — it converts long-shot 1/32 rolls into reliable inheritance and slashes the expected egg count.