Cat Pregnancy Calculator (Queening Date)

Background.

Your queen spent a long weekend with a stud tom, or slipped out to meet the neighbour's, and now you want to know when to have a kittening box ready. For a cat that question has a surprisingly firm answer, firmer than for almost any other pet. A queen does not release eggs on a hormonal clock of her own. Mating itself sets off the luteinising-hormone surge that makes her ovulate, so the day you saw her mate is, for practical purposes, the day the pregnancy started.

The Merck Veterinary Manual puts parturition in the queen at 64 to 66 days from that copulation-triggered surge, and its table of approximate gestation periods lists 65 days for the cat. Compare a bitch bred on an unknown day of a heat that can run three weeks: from an untimed mating the same manual can only offer 58 to 72 days. Induced ovulation is what buys the cat its narrow range.

Narrow, though, is not the same as fixed. When Root Kustritz, Johnston and Olson timed fifteen pregnancies in a feline research colony in 1995, gestation averaged 66.9 ± 2.9 days, with a range from 62 to 71. VCA's veterinary authors quote 60 to 67 days, averaging 63 to 65, and Merck's own cat-owner page gives 64 to 66 days after breeding in one place and 60 to 65 days in another. Rather than blend these into one confident number, you choose between Merck's clinical figure and the measured colony, and the note under the result names the source that dated it.

Alongside the due date you get the dates that actually shape the next nine weeks: when a vet can first confirm the pregnancy, when her food should go up, and how far the birth window stretches when she was with the tom for several days. None of this diagnoses pregnancy or replaces your veterinarian, and no medicine or wormer dose appears anywhere here.

What is cat pregnancy calculator?

Feline gestation is the interval from ovulation to queening, the birth of the litter. In the cat, ovulation is induced: stimulation of the vagina and cervix during mating triggers the LH surge, and a single mating may not be enough, which is why Merck advises several breedings over two or three days. Because ovulation follows mating so closely, gestation can be counted from the mating date itself, and that count runs about nine weeks. Inside it sit a few fixed landmarks. Nothing can be reliably detected before roughly day 21. Palpation and ultrasound can confirm the pregnancy from day 21 to day 30 after breeding. Fetal skeletons show on an X-ray from around day 45, which is when kittens can be counted. Energy needs climb in the last three weeks as the kittens gain most of their birth weight, and the first stage of labour, mostly restlessness and nesting, comes in the day or so before the first kitten.

How to use this calculator.

1. 01Enter the first day you saw her mate, not the last. If she roams outdoors and you never saw a mating, there is no date to count from, and an ultrasound is the way to stage the pregnancy.
2. 02Enter how many consecutive days she had access to the tom, from 1 to 7. Use 1 for a single observed mating; a planned breeding is usually two or three days. If she had unsupervised access for longer than a week, no window can be estimated.
3. 03Choose the published figure. The clinical option gives Merck's 65 days with a three-day window; the observed-colony option gives a 67-day estimate and a much wider window that reflects how real pregnancies spread out.
4. 04Leave today's date as it is, or set a later date to see where she will be then, for example the day before you go away for a weekend.
5. 05Copy the confirmation window, the food step-up date and the birth window into a calendar, and book the vet visit inside the confirmation window rather than before it.

The formula.

Every date is counted in whole calendar days from the first mating. The expected queening date is mating + L, where L is 65 days on the clinical figure and 67 days on the colony figure; 67 is the colony's 66.9-day mean rounded to the nearest day, and the result note says so whenever that figure is in use. The birth window runs from mating + lo to mating + hi + (s − 1), where lo and hi are 64 and 66 days for the clinical figure or 62 and 71 days for the colony, and s is the number of days she had access to the tom. The reasoning behind (s − 1): if she mated on three consecutive days, any one of them could have triggered ovulation, so the latest plausible birth moves two days later, while the earliest plausible birth, still tied to the first mating, stays put. The point estimate is never moved by the mating span. The confirmation window is mating + 21 to mating + 30 for both figures, straight from Merck's breeding-management guidance. The feeding step-up is the queening date minus 21 days, which falls on day 44 of gestation on the clinical figure and day 46 on the colony figure. Days to go is L minus the gestation day, so it turns negative once the expected date has passed. The stage message reads the gestation day against these landmarks in order: too early to confirm (before day 21), confirmation window open (21 to 30), mid gestation, last three weeks (from the step-up day), birth window open (from lo), and past the window. Two inputs are refused rather than guessed at: a today earlier than the mating date, and a gap of more than 400 days between them, which can only mean one of the dates is wrong. The main assumption is that ovulation followed the first mating you saw. If she also mated unseen before that date, every date here will be too late.

A worked example.

Frequently asked questions.

References& sources.

1. [1]MSD/Merck Veterinary Manual, "Whelping and Queening in Bitches and Queens" (Autumn P. Davidson, DVM, MS, DACVIM; last reviewed June 2025) — "Parturition in the queen occurs 64–66 days from the LH surge triggered by copulation."
2. [2]MSD/Merck Veterinary Manual, "Breeding Management of Queens" (Davidson; last reviewed July 2025) — "Evaluation for pregnancy can be performed by abdominal palpation and ultrasonography 21–30 days after breeding"; multiple breedings over 2–3 days are advised because ovulation is induced by vaginal-cervical stimulation.
3. [3]MSD/Merck Veterinary Manual, "Management of Reproduction of Cats" (cat-owner version; last reviewed August 2025) — delivery "typically occurs 64 to 66 days after breeding"; the same page also states "Pregnancy lasts 60 to 65 days"; queens need "25% more food during the last 3 weeks" and 2–3 times normal intake while nursing; stage I labour lasts "12 to 24 hours".
4. [4]MSD/Merck Veterinary Manual, table "Approximate Gestation Periods" — Cat: 65 days.
5. [5]Root Kustritz MV, Johnston SD, Olson PN (1995). "Estrous length, pregnancy rate, gestation and parturition lengths, litter size, and juvenile mortality in the domestic cat." Journal of the American Animal Hospital Association 31(5):429–433 — "Gestation length averaged 66.9 +/- 2.9 days with a range of 62 to 71 days (n = 15)"; average estrous length 5.8 ± 3.3 days; average litter 3.7 kittens.
6. [6]VCA Animal Hospitals, "Pregnancy and Parturition in Cats" (Courtney Barnes, BSc, DVM; Krista Williams, BSc, DVM, CCRP; Ernest Ward, DVM) — "Pregnancy or gestation ranges from 60–67 days, averaging 63–65 days"; fetal skeletons visible on X-ray for counting at around day 45; first-stage labour "can last up to 36 hours" in a queen having her first litter; nutrient requirement reaches one-and-a-half times pre-pregnancy level.