Why does a 12.5% female Pokémon show 12.1%?

The games store the gender ratio as a number out of 256. Starters and other "1 in 8" species get 31 of 256, which is 12.1% female.

Why does the Everstone show 52% and not 50%?

The Everstone wins a coin flip half the time. When it loses, the Nature is random and still matches 1 time in 25, which adds 2%.

Why does the HP IV rarely pass down in Emerald?

Emerald picks three stats to copy but can pick the same one twice, and HP only gets picked 1 time in 6. Ruby and Sapphire have a smaller version of the same bug.

Emerald Breeding Calculator: Egg Chance, Steps & IVs

Pick two Pokémon: Egg chance, steps to the Egg and to hatch, gender, Nature, IVs and egg moves in Pokémon Emerald, Ruby and Sapphire.

Pick your game and the two Pokémon you leave at the Day Care; the answer updates as you go.

Emerald Breeding Calculator: Egg Chance, Steps & IVs — Pokémon Ruby, Sapphire & Emerald guide card

Published 23 Oct 2026

The interactive calculator runs in your browser. Its default example:

Emerald: a female Mudkip and a male Spheal, both caught by you
Egg chance	20% every 256 steps (“The two don’t seem to like each other much.”)
First Egg	~1,279 steps on average, 9 in 10 by 2,815 steps
Baby	Mudkip, ♂ 87.9% · ♀ 12.1%
Hatching	5,375 steps, 2,815 steps with Flame Body or Magma Armor in the party
Nature	Random; 52% the mother’s with an Everstone
Shiny	1 in 8,192
IVs	three from the parents 53.3% of the time; HP only 16.7%
Egg moves	Ice Ball (Spheal learns it at level 13)
Ball	Poké Ball, level 5

Reading the answer: Egg chance, IVs and egg moves in Gen 3

Every 256 steps the game rolls once for an Egg, so "20% every 256 steps" means about 1,300 steps on average. The hatch count starts when you take the Egg. The mother decides the species; the father passes on the egg moves he knows. In Emerald only, an Everstone on the mother or Ditto passes her Nature about half the time, and Flame Body halves the hatch steps.

Where the Day Care is, how to collect the Egg and where to catch Ditto: the Ruby, Sapphire & Emerald breeding guide.

Breeding calculator FAQ

Why does a 12.5% female Pokémon show 12.1%?: The games store the gender ratio as a number out of 256. Starters and other "1 in 8" species get 31 of 256, which is 12.1% female.
Why does the Everstone show 52% and not 50%?: The Everstone wins a coin flip half the time. When it loses, the Nature is random and still matches 1 time in 25, which adds 2%.
Why does the HP IV rarely pass down in Emerald?: Emerald picks three stats to copy but can pick the same one twice, and HP only gets picked 1 time in 6. Ruby and Sapphire have a smaller version of the same bug.

Daily Pokémon location quiz on Instagram: @pokemaps_

Explore PokéMaps: Interactive Pokémon maps for every region

More guides for this game

Ruby, Sapphire & Emerald Tips: Controls & Hidden Tricks — Reorder moves with SELECT, sort the Bag, register a bike or rod, use the Repel trick and soft reset in Pokémon Ruby, Sapphire and Emerald.
Emerald Breeding Guide: Day Care, Eggs, Ditto & Everstone — Which pairs make Eggs in Pokémon Ruby, Sapphire and Emerald, what babies inherit, hatch steps, Ditto and the Everstone trick.
Gen 3 Shiny Hunting: Odds & Soft Resets in Emerald — Shiny odds of every method, soft-reset steps, Emerald’s timing trap and the best targets in Ruby, Sapphire and Emerald.
Emerald TM Locations: Where to Get All 50 TMs — All 50 TMs in Emerald, Ruby and Sapphire in story order: gifts, item balls, shops and Game Corner prizes, and what each one needs.
Emerald Item Locations: Key, Held & Evolution Items — Where to get the key, held and evolution items in Emerald in story order: rods, bikes, Exp. Share, Leftovers, every stone and the Lilycove shops.
Emerald Battle Frontier Strategy: Teams, BP & Tips — How to win at the Emerald Battle Frontier: what to buy with BP, the best Battle Palace natures, how the Arena judges score, and Scott’s rewards.

Browse all guides