Mewgenics Breeding Calculator
The only calculator built from the game's actual code — not guesswork.
Every kitten is determined by one function — glaiel::CatData::breed — with 13 steps governing stat inheritance, spells, passives, disorders, and birth defects. Other tools use 4 stats and averages; the real game uses 7 stats and picks one parent's value per stat. This calculator uses the formulas reverse-engineered by SciresM from the compiled binary, so you get accurate odds for better stats, ability inheritance, and inbreeding risks.
- 7 stats (STR, DEX, CON, INT, SPD, CHA, LCK) — one parent per stat, never averaged
- Stimulation breakpoints: 32 = first spell guaranteed, 95 = passive guaranteed
- 15% per parent to pass a disorder; birth defect odds scale with inbreeding
- Spec-complete: stat inheritance, spell/passive odds, disorders, birth defect parts, body part & mutation logic
Calculator
Enter each parent's base stats (STR, DEX, CON, INT, SPD, CHA, LCK), your room's Stimulation value, and the pair's inbreeding coefficient (0 for strays). Only base stats are inherited; gear and class collars do not pass to offspring. Unlock base-stat display by donating kittens to Tink (around 60 for the split view).
Parent base stats (STR, DEX, CON, INT, SPD, CHA, LCK)
Enter each parent's base stats only — gear, collars, and buffs don't pass to offspring. Unlock base-stat display at Tink's ~60 kitten milestone. Strays cap at 7 per stat; breeding can exceed.
Parent 1 (e.g. mom)
Parent 2 (e.g. dad)
Room Stimulation & inbreeding coefficient
Breakpoints: 32 = first spell guaranteed; 95 = passive guaranteed. Only room stat that affects breed formulas.
Strays = 0. Unlock display at Tink (40 donations). Raises birth defect disorder & parts; exact game formula not yet published.
Stimulation reference
| Stim | P(better stat) | 1st spell | Passive |
|---|---|---|---|
| 0 | 50% | 20% | 5% |
| 25 | 55.6% | 82.5% | 30% |
| 32 | 56.4% | 100% | 37% |
| 50 | 60% | 100% | 55% |
| 95 | 66.1% | 100% | 100% |
| 100 | 66.7% | 100% | 100% |
| 200 | 75% | 100% | 100% |
Predicted outcomes
Stat inheritance (per stat)
Each stat is taken from one parent's value — never averaged. Probability of getting the higher of the two:
Spell & passive inheritance
- First spell: 20.0%
- Second spell: 2.0%
- Passive: 5.0%
Skill Share+ guarantees the other equipped passive is passed; Skill Share itself is excluded from the normal passive pool.
Disorders (127 in game)
- From mother: 15% (one random disorder; independent roll)
- From father: 15% (one random disorder; independent roll)
- Birth defect disorder: 2.0% — only rolled if the kitten got 0 or 1 disorder from the parents above. Scales with inbreeding (2% baseline at IC ≤ 0.2).
Max 2 disorders per cat. Room furniture does not change these odds.
Birth defect parts (visual deformities)
0.0% chance of deformed body parts (impossible at IC ≤ 0.05).
Body part inheritance
80% all parts from parents; 20% one part-set randomly assigned. Mutations are part variants; when only one parent has a mutated part, Stimulation uses the same formula as stat inheritance to favor the mutation.
Quick tips
- Keep 4 or fewer cats per room to avoid Comfort penalty; clean poop.
- Aim for Stimulation 32+ to guarantee first spell, 95+ for passive.
- Stimulation never reaches 100% better-stat odds — even at 200 it's 75%.
- Breed with strays to reset inbreeding (strays have zero kinship with house cats).
Why use this Mewgenics breeding calculator?
No other public calculator implements the actual datamined formulas. NKBGaming's tool uses 4 stats and averages parent values; the game uses 7 stats and picks one parent per stat. Mewgenics.org's calculator returns errors. This tool is built from SciresM's reverse engineering of glaiel::CatData::breed — the only public source derived from real game code — so you get correct Stimulation curves, disorder probabilities, and inbreeding-dependent birth defect risks.
How Mewgenics breeding works
Breeding happens at home between adventure runs, during the overnight phase. You place compatible cats in the same room (heterosexual male + female, or any gender with a Ditto, or bisexual cats), optimize room furniture for Comfort and Stimulation, then end the day. Overnight, cats may breed (1–2 kittens), fight, or do nothing. You cannot choose which pair mates — only which cats share a room. Comfort determines whether cats breed or fight; keep 4 or fewer cats per room and clean poop to avoid penalties. Wiki has full breeding and room mechanics.
Tink's unlock milestones
Donate kittens to Tink to unlock breeding-related info (10 kittens per milestone):
- 10 — Symbol/icon for cat tracking
- 20 — Libido indicator
- 30 — Aggression indicator
- 40 — Inbreeding status display
- 50 — Sexuality flags ("Gaydar")
- 60 — Base stats vs. bonus stats (essential for this calculator)
- 70 — Family tree viewer
The seven base stats
Kittens inherit one parent's value per stat — never an average. The game rolls independently for each of the seven stats: Strength (STR), Dexterity (DEX), Constitution (CON), Intelligence (INT), Speed (SPD), Charisma (CHA), and Luck (LCK). Only base stats are inherited; bonuses from gear, class collars, buffs, injuries, and status effects are ignored. Stray cats cap at 7 in any single base stat; selective breeding can push stats higher.
- STR — melee attack and melee ability damage
- DEX — ranged attack and ranged ability damage
- CON — max HP and post-combat regeneration
- INT — mana regeneration rate
- SPD — turn order and movement range
- CHA — max mana and starting mana
- LCK — base crit chance and general randomness
Body shapes and build optimization
Body parts use a Mendelian two-allele system. Head shape (Triangle = Mage, Square = Tank, Round = balanced), body shape (Slender = Rogue/Speed, Fat = Tank, Average = no bonus), and tail shape (Long = range, Stubby = knockback, Curly = carry capacity) affect stat aptitude and ideal class. Pure shape combos (e.g. Square head + Fat body) outperform hybrids. Shape inheritance follows the same dominant/recessive rules as other parts; the exact dominance hierarchy for shapes is not yet fully datamined.
Stimulation and room stats
Stimulation is the main room stat that affects breeding quality. It increases the chance the kitten gets the better of the two parents' stats, and raises spell and passive inheritance odds. Key breakpoints: at 32 Stimulation the first spell is guaranteed; at 95 passives are guaranteed. At 100 Stimulation, the better-stat probability is about 66.7%. The formula never reaches 100% — Stimulation is intentionally modest. Other room stats: Comfort (breeding vs. fighting), Health (disease spread; 10+ can cure disorders), Mutation (overnight mutation chance), and Appeal (house-wide, stray quality). Furniture like Toxic Waste Barrels boost Stimulation at the cost of Comfort; balance both for best results.
Inbreeding coefficient
The game uses a system inspired by Wright's coefficient of inbreeding (COI), tracking kinship across the full pedigree. Stray cats have zero kinship with house cats, so they reset inbreeding. The exact in-game formula has not been published; Wright's COI is the best approximation for calculators. Higher inbreeding raises the chance of birth defect disorders (extra disorder roll) and birth defect parts (visual deformities). At coefficient 0.05 or below, birth defect parts are impossible; at 0.5 there is about a 75% chance. Tink unlocks inbreeding status display at 40 kitten donations.
Disorders and birth defects
The game has 127 confirmed disorders (physical and mental). Each parent has a 15% chance to pass one random disorder to the kitten (independent rolls). An additional birth defect disorder can occur only if the kitten got 0 or 1 disorder from the parents; that probability scales with inbreeding (2% baseline at IC ≤ 0.2, up to 42% at 1.2+). A separate roll determines birth defect parts (visual deformities), possible only when inbreeding > 0.05; at IC > 0.9 the game applies birth defect parts twice. Max 2 disorders per cat. Room furniture does not change disorder odds.
Frequently asked questions
- What is Stimulation in Mewgenics?
- Stimulation is a room stat (Yarn Ball icon) that improves breeding outcomes: it increases the chance the kitten gets the higher of the two parents' stats and raises spell and passive inheritance probabilities. First spell is guaranteed at 32+ Stimulation; passives at 95+. It is the only room stat that feeds directly into the breed formulas. SciresM noted it is "surprisingly weak" — the formula never reaches 100% better-stat odds.
- How does stat inheritance work?
- For each of the seven stats (STR, DEX, CON, INT, SPD, CHA, LCK), the kitten gets one parent's value at random — never an average. The probability of getting the better (higher) value is (1 + 0.01×Stimulation) / (2 + 0.01×Stimulation). At 0 Stimulation that is 50%; at 100 it is about 66.7%.
- How do I see base stats for the calculator?
- Donate kittens to the NPC Tink. At around 60 donations you unlock the base stats vs. bonus stats split view. Before that, you only see total stats (base + gear, collar, mutations, etc.), so you can't plug accurate numbers into a breeding calculator. Stray cats cap at 7 in any single base stat; breeding can push higher.
- What is the inbreeding coefficient?
- A value (0–1.5+) that reflects how related the parents are. The game uses a recursive, pedigree-based system inspired by Wright's COI. Stray cats have zero kinship with house cats — use them to reset inbreeding. Higher values increase birth defect disorder and birth defect parts chances. Unlock the inbreeding display via Tink at 40 kitten donations.
- What is Skill Share+?
- A passive that guarantees your other equipped passive is passed to offspring when breeding. Skill Share itself cannot be inherited through the normal passive roll — only via Skill Share+. Class spells can also be favored in parent selection (0.01×Stimulation chance to favor the parent with class spells).
- Do traits follow Mendelian genetics?
- Yes. The game has 79+ traits with dominant/recessive alleles (e.g. Strong dominant, Weak recessive, Lucky recessive). The wiki documents 24 with dominance. Standard Mendelian tables apply (e.g. Aa×Aa → 25% AA, 50% Aa, 25% aa). Mutations are body part variants (~52), not a separate genetic system; they inherit via the same Stimulation formula when only one parent has the mutation.
- Why do other Mewgenics calculators get it wrong?
- No other public calculator uses the datamined formulas. Some use 4 stats instead of 7, average parent stats instead of picking one per stat, or invent mechanics (e.g. elemental breeding). This tool is based on SciresM's reverse engineering of the game binary — the only public source from actual game code.
About this calculator
The formulas used here come from SciresM's reverse engineering of the game binary — the only public source derived from actual game code. The breed logic lives in glaiel::CatData::breed and runs 13 steps: furniture effects, stat inheritance, Skill Share+ application, spell and passive inheritance, disorder inheritance, birth defect rolls, body part (and mutation) inheritance, symmetrization, unknown/voice inheritance, and birth defect application. The exact inbreeding coefficient calculation has not been published; we use the same probability formulas the game uses once the coefficient is known. For more detail, see the technical specification and the wiki.