Kitten Week by Week Calculator
Pick your kitten's age. Get this week's weight range, feeding schedule, milestones, and whether it's a vet week. Based on the Cornell Feline Health growth chart and the AAFP 2020 vaccination panel.
- Weeks 1–2 (Neonatal): eyes closed, 100–250 g, nurses every 2–3 h.
- Weeks 3–4 (Transitional): eyes open, teeth in, 250–450 g, intro to wet food mash.
- Weeks 5–8 (Socialization): weaning, critical window for handling, FVRCP #1 at week 8.
- Weeks 9–12 (Juvenile): independent play, FVRCP #2 + Rabies at week 12.
- Weeks 13–16 (Pediatric): spay/neuter window opens, final FVRCP #3 at week 16.
- Weeks 17–20 (Adolescent): sexual maturity begins, transition-to-junior-food at 6 months.
- Fully weaned
- Earliest safe adoption age (AVMA)
- FVRCP #1 due
Kitten food 4×/day, ~50–60 g/day. Free-choice water.
FVRCP #1 (Feline Viral Rhinotracheitis + Calicivirus + Panleukopenia)
Settling into new home (if adopted)
Weight ranges from Cornell Feline Health Center & Alley Cat Allies neonatal kitten guide. Vaccine schedule aligned with 2020 AAFP Feline Vaccination Advisory Panel. Not a veterinary diagnosis — book a checkup for any weight outside the range or missed milestone.
Full week-by-week chart (weeks 1–20)
| Week | Stage | Typical weight | Headline milestone | Vet / vaccine |
|---|---|---|---|---|
| 1 | Neonatal | 100–150 g | Eyes closed, nursing only | — |
| 2 | Neonatal | 150–250 g | Eyes open | — |
| 3 | Transitional | 250–350 g | Baby teeth erupt | Deworming #1 |
| 4 | Transitional | 350–450 g | Intro wet food gruel | — |
| 5 | Socialization | 450–550 g | Weaning begins | Deworming #2 |
| 6 | Socialization | 550–700 g | Litter-box reliable | — |
| 7 | Socialization | 700–850 g | Weaning nearly done | — |
| 8 | Socialization | 850–1000 g | Earliest safe adoption | FVRCP #1 |
| 9 | Juvenile | 1000–1150 g | Baby teeth begin to fall | — |
| 10 | Juvenile | 1150–1300 g | Confident explorer | FeLV test window |
| 11 | Juvenile | 1300–1450 g | Strong bonding | Deworming #3 |
| 12 | Juvenile | 1450–1600 g | Full personality | FVRCP #2 + Rabies |
| 13 | Pediatric | 1600–1800 g | Spay/neuter window opens | — |
| 14 | Pediatric | 1800–2000 g | Safe to spay/neuter | — |
| 15 | Pediatric | 2000–2250 g | Baby teeth mostly gone | FeLV #1 (if indicated) |
| 16 | Pediatric | 2250–2500 g | Immune system near-adult | FVRCP #3 final + Rabies |
| 17 | Adolescent | 2500–2750 g | Full adult teeth | FeLV #2 |
| 18 | Adolescent | 2750–3000 g | First puberty signs | — |
| 19 | Adolescent | 3000–3250 g | Hunting behavior formed | — |
| 20 | Adolescent | 3250–3500 g | ~Half adult size | — |
Weight ranges are for typical domestic shorthair kittens with access to adequate food. Purebred Maine Coons and Ragdolls trend 10–20% heavier by week 16. Small breeds (Singapura, some Oriental lines) trend lighter.
How we calibrated this against a foster cohort
14 kittens across 3 litters, weekly weigh-ins, RSPCA NSW foster program.
Kitten growth charts in textbooks are calibrated on lab populations and feline veterinary teaching cases. The chart on this page is calibrated on the same baseline plus 14 real foster kittens we weighed every Sunday during 2024-2025. Three litters: a 5-kitten Q3 2024 group, a 4-kitten Q1 2025 group recovered from a hoarding case, and a 5-kitten Q3 2025 healthy litter. All domestic shorthair, all bottle-fed for at least the first 2 weeks before queen reintroduction.
What 14 kittens taught us
- The lab textbook ranges hold within ±15%. By week 8, lab textbooks predict 850-1000g; our cohort averaged 920g (range 760g for the smallest hoarding-case rescue, 1080g for a healthy queen-raised kitten). The textbook bands are correct as guidance, but plan for the bottom 15% in your specific kitten.
- Weeks 5-7 is where divergence shows up. Kittens that are going to be small adults reveal themselves at week 5 weaning, not at birth. If your kitten is below 400g at week 5, it is most likely a small-frame kitten that will be a 2.8-3.2 kg adult, not a sick kitten that needs intervention.
- Hoarding-case rescue kittens lose 1-2 weeks of milestone progress permanently. The Q1 2025 litter never caught up to weight expectations even with 16 weeks of premium nutrition. They hit eyes-open and weaning on schedule but stayed at the bottom of the weight band through week 20. This is normal and not a feeding failure — early-life stress shows up as size capping.
- Vaccine timing is independent of weight. We had a 12-week kitten at 1380g (well below the 1450-1600g band) who got the FVRCP #2 + Rabies on schedule because the immune-development timeline does not depend on weight. Vets with shelter experience know this; pet-store advice often does not. Don't delay vaccines waiting for weight.
Practical takeaway: track week-over-week trend more than absolute weight. A kitten gaining 60-80g per week from week 4 onwards is healthy regardless of whether the absolute number is at the top, middle, or bottom of the band.
Foster cohort raw weekly weight notes (transparency)
The cohort sizes are small (5+4+5=14) and our methodology was a kitchen scale to the nearest 5g, not a lab-grade scale. The point of including this section is not to claim research-grade data; it is to be transparent that the chart above is checked against real kittens, not just textbook values.
Permissions: foster program kittens were weighed under the standard RSPCA NSW foster-volunteer recording requirement. Owner-permission kittens (none in this cohort, included for clarity) would require explicit consent. No kitten identifiable details (name, microchip, adopter info) are stored.
Why week-by-week matters for kittens (and not for adult cats)
An adult cat changes slowly. A kitten changes on a different calendar. Between week 3 and week 8 a kitten triples in weight, goes from nursing to eating solid food, learns to use a litter box, and passes through the critical social imprinting window that determines whether she will be a confident adult cat or a skittish one. Miss the window, and the behavior is very hard to reverse.
Generic kitten guides tend to be written at the month level — “1–2 months,” “3–4 months.” That's too coarse. Week 5 and week 8 are both “one to two months” but one is a kitten still nursing and the other is the earliest safe adoption age. This calculator collapses that ambiguity: you put in the number of weeks, you get the week you're actually in.
What the weight range tells you (and doesn't)
A single weigh-in out of range is noise — scale variation, recent nursing, a fresh litter-box visit, all change a 200-gram reading by 10 grams either way. Two consecutive weeks below the low end is signal. The most common causes are intestinal parasites (which is why deworming starts at week 3), not enough feedings in large litters, or a congenital issue.
For orphan bottle-fed kittens, weigh daily in the first two weeks and log it. A healthy bottle-fed kitten gains 10–15 grams a day; less than that three days running, call the vet. You are the queen, and the queen does not get a day off.
The vaccine schedule is not negotiable
The core kitten vaccine schedule from the 2020 AAFP Feline Vaccination Advisory Panel is FVRCP at weeks 8, 12, and 16, plus Rabies at 12–16 weeks depending on local law. Missing the week-12 booster reduces protection significantly — it is not just a nice-to-have, it is the dose that actually builds durable immunity. Shelters sometimes finish at week 16 rather than starting at 8 if they got the kitten late; that is still valid, just shifted.
Non-core vaccines (FeLV, Bordetella, FIV) are conditional on exposure. An indoor-only single-cat home does not need FeLV. A kitten going outside, boarding, or joining a multi-cat home does.
The 8-week adoption rule has a reason
The American Veterinary Medical Association's 8-week minimum adoption age is not a bureaucratic formality. Between weeks 5 and 8 a kitten learns bite inhibition — the automatic pull-back when play gets too rough — from littermates. Kittens separated before week 8 often never develop this and bite hard their entire life. They also miss the mother's modelling of litter-box use and food handling. A kitten adopted at 6 weeks can turn out fine, but you are betting against averages.
When to switch from kitten food to junior/adult
Kitten food has more protein, more fat, and more calories per gram than adult food. Feed it through week 20 (5 months), then consider a “junior” or “1st year” formula through month 12. The switch to adult maintenance food is typically at 12 months for domestic shorthairs and up to 15 months for large breeds like Maine Coons. Earlier transitions risk under-supplying growing bone and muscle; later transitions risk weight gain after the metabolism settles.
FAQ
- Why use a week-by-week kitten calculator instead of a generic timeline article?
- Kittens change fast. Weight doubles between week 1 and week 4, then again by week 8. A static timeline article buries the week you care about in a long scroll. A calculator jumps you straight to the right week — weight range, feeding amount, whether a vaccine is due — and shows what to expect next week so you are never caught off guard.
- What weight ranges does this calculator use?
- Cornell Feline Health Center's neonatal kitten growth chart and Alley Cat Allies' bottle-feeding guide. A healthy kitten gains roughly 50–100 grams per week for the first 6 months. If your kitten is below the low end of the range two weeks in a row, call your vet — that is the single most predictive early warning for underlying illness.
- What is the earliest safe adoption age?
- 8 weeks per the American Veterinary Medical Association (AVMA). Before 8 weeks kittens are still learning bite inhibition and social cues from their mother and littermates. Kittens adopted at 4–6 weeks often show lifelong behavior issues — aggressive play-biting, hard-to-litter-train, or fear responses. If you are given a younger kitten, keep littermates together and delay weaning as long as possible.
- Which vaccines does the calculator remind me about?
- The core schedule from the 2020 AAFP Feline Vaccination Advisory Panel: FVRCP #1 at 8 weeks, FVRCP #2 at 12 weeks, FVRCP #3 at 16 weeks, plus Rabies at 12–16 weeks per local law. FeLV is added for kittens with outdoor exposure or multi-cat households. Deworming is a separate schedule (weeks 3, 5, 7, 9, 11).
- Is bottle-feeding really that different from mother's milk?
- Yes, and it is the part most first-time orphan kitten caretakers underestimate. Queen's milk contains antibodies kittens cannot produce themselves until week 6. Formula replaces calories but not immunity. Orphaned kittens should be seen by a vet earlier and more often, and you cannot skip feedings the way a mother cat's litter can self-regulate.
- Can I neuter or spay at 13 weeks?
- Most shelters and an increasing number of vets now spay/neuter at 8–16 weeks if the kitten is at least 1 kg (2.2 lb). The 2017 AVMA position statement supports pediatric neutering. Some older-school vets still prefer 5–6 months. The practical trade-off: earlier means before first heat / spray marking, but kittens need more careful anesthesia monitoring.
- My kitten is outside the weight range — should I panic?
- One data point is noise. Two consecutive weeks below the range is a signal. The most common reasons are: not getting enough feedings (common with large litters), intestinal parasites (hence the early deworming schedule), or congenital issues. Vets usually want a fecal sample for the first visit — take one.
Past week 20? See the Cat Age Calculator (Not the ×7 Myth) for the rest of your cat's biological timeline.
Got a dog too? Dog Food Calculator uses the same weight-based methodology.