Cat Pregnancy Calculator

A cat gives birth about 65 days after first mating, and most litters arrive between days 61 and 70

A cat's pregnancy lasts about 65 days on average. In a survey of 1,056 UK pedigree litters the average was 65.1 days, with 90.2% born between days 63 and 67 and 97.1% between days 61 and 69. A 2022 review of feline breeding says 95-97% of queens give birth 61-70 days after mating. The familiar "63 days" may be counted from the last mating, so counting from the first mating puts the date about two days later.

This calculator works out the due date and expected range from the first and last mating dates and breed, or from a vet's ultrasound measurements. It also shows which day of pregnancy it is today, and lists the to-dos in date order, from the vet check to feeding more, setting up a birthing spot, the X-ray and the call-the-vet date, plus a pregnancy calendar with one square per day that shows what changes that week. If the first mating was on October 1, 2026, the due date is Saturday, December 5, 2026 and the expected range runs from Tuesday, December 1 to Thursday, December 10.

Why work out the due date ahead of time

A pregnant cat shows few outward changes early on, so without a date on the calendar it is easy to miss the moments that matter.

• Timing the vet visit: the best time to confirm pregnancy by palpation and ultrasound is 21-30 days after mating. Earlier is hard to confirm, and after day 35 individual kittens are hard to tell apart by palpation.
• When you do not know the mating date: for a cat that goes outdoors, an ultrasound measurement lets you count back to the birth date. Each stage uses a different measurement, so it helps to know roughly where she is.
• Changing and increasing her food: kitten food is recommended during pregnancy, and in the last 3 weeks she should eat 25% more than usual. Do not give extra supplements such as calcium or vitamins.
• Setting up the birthing spot: put a box in a quiet, warm place by 2 weeks before the due date so she gets used to it. In the last week she will look for a place to give birth on her own.
• Knowing how many kittens to expect: an X-ray count makes it easier to tell whether the birth is finished. Bones show from about day 45, and counting is easy after day 55.
• Deciding when to go to the vet: if there are no signs of birth after 71 days from mating, a C-section is recommended to protect the kittens. Knowing that date in advance cuts down on hesitation.

How the calculation works

When counting from mating, the first mating date is day 0 and the due date is 65 days later. If you choose a breed, the calculator adds that breed's average gestation, rounded to whole days. The expected range runs from first mating + 61 days to last mating + 70 days. When counting from a vet exam, it works out the days left until birth from the ultrasound measurement and adds them to the exam date.

Counting back from ultrasound measurements

In the first half of pregnancy (days 19-37) the gestational sac diameter (ICC) is used, and from day 38 the kitten's head width (BP). The formulas given in a 2022 review of feline breeding (Holst) take the value in mm and return the days left until birth. Body diameter (BD) uses the feline formula from the MSD Veterinary Manual, takes the value in cm and applies after day 40. The calculator rounds the days left and adds them to the exam date.

In an analysis of dog and cat scans together (Beccaglia and Luvoni 2012), 85.9-93.1% of ICC measurements taken in weeks 4-5 and 82.3-95.2% of BP measurements taken in weeks 5-8 were within ±2 days, while BP measured in week 9 fell to 69.8%. The MSD manual also puts the error of the feline ultrasound formulas at ±2 days, so the calculator shows the due date ±2 days as the range. Holst (2022) notes, however, that the accuracy of such formulas depends on when the measurement is taken and drops closer to birth. In the study by Keiser and colleagues (2017), head width measured within 5 days of birth hit the birth date 27-53% of the time, and body diameter 17-35%. Maine Coons have their own formula (Socha and Janowski 2019); with the same ICC of 20 mm it gives 42.1 days left, about 4 days more than the general formula. If your report is written in cm, switch the unit to cm.

Why 65 days and not 63

Older sources and many handouts give the cat's pregnancy as 63 days. The UK survey (Sparkes 2006) found an average of 65.1 days, and it cites earlier work noting that the older "around 63 days" reports may have counted from the last mating rather than the first. Cats often mate several times over a few days, so the starting day you choose changes the result by 2-3 days. The Merck Veterinary Manual also says birth usually happens 64-66 days after mating.

Example: mating around October 1, 2026

For the same pregnancy, the due date and range change with what you know. With only the mating date the range is more than 10 days, and with an ultrasound measurement it narrows to 5.

Average gestation by breed

Breed affected gestation length even when other factors were held apart (Sparkes 2006). Siamese and Oriental Shorthair were longest at over 66 days, and the Korat was shortest at 63. The calculator adds the average, rounded to whole days, to the first mating date. For breeds with around 30 litters (Maine Coon, Tonkinese, Exotic Shorthair and others) the average can wobble.

Some sources give 63 days for the Siamese (Root Kustritz 2006), but in the 1,056-litter survey above it was among the longest at 66.1 days. Litter size has an effect too, but a small one: each extra kitten shortened gestation by 0.1 day on average. In the same survey a litter averaged 4.6 kittens, and 8.0% were born by C-section. The C-section rate ranged from 0 to 18.5% by breed, but once other factors were considered, the effect of breed itself was not clear.

Mother, kittens and to-dos by week

The weeks below are counted with the first mating date as day 0. In the calculator's pregnancy calendar, selecting a square shows the week containing that date in the same format.

Signs of labor and when to call the vet right away

As birth nears, in the last week she looks for a place to give birth, and in the last 24 hours she may stop eating and her rectal temperature may drop below 37.8 °C (100 °F). In stage 1 she goes back and forth to her birthing spot, may scratch at the bedding to arrange it, seek out people or pant. In the UK survey 82.9% finished this stage within 2 hours, though for a first litter it can last up to 36 hours. In stage 2 she strains for about 5-30 minutes per kitten, kittens usually arrive 10-60 minutes apart, and they are all born within 6 hours as a rule.

• Call right away: she strains hard for 20-30 minutes and no kitten comes out
• Call right away: a kitten is visible at the opening but has not come out after 10 minutes
• Call right away: a lot of blood or green discharge with no kitten, or bright red blood flows for more than 10 minutes
• Call right away: she is weak and listless, or her rectal temperature is above 39.4 °C (103 °F)
• Ask for advice: stage 1 lasts over 24 hours with no straining, or no next kitten arrives within 1 hour after the first
• Get her seen: no signs of birth after 71 days from mating

Note A little green discharge after a kitten or placenta has come out can be normal. Red-brown discharge after birth can continue for up to 3 weeks, but if it is green or smells bad, have her seen (Cats Protection).

Common mistakes

• Counting from the last mating date: if she mated on several days, make the first day day 0 and use the last day to extend the end of the range. Counting from the last day puts the due date a few days late.
• Trusting a single day, 63: counted from mating, birth on day 61 or on day 70 is within the normal range. Look at the start and end of the range, not only the due date.
• Using a dog's ultrasound formula: dogs and cats use different formulas. For example, "6 × GSD + 20" is a dog formula. For a cat's report, use the cat formula.
• Mixing up mm and cm: the ICC and BP formulas use mm, the BD formula uses cm. The calculator can switch units, and warns you if a value is larger than the size at birth.
• A measurement that does not fit the stage: ICC is for up to about day 37, and BP from day 38. If the stage does not match, a warning appears under the result.
• Relaxing because her temperature has not changed: a temperature drop only means "it can happen", and not every cat shows it. Watch it together with appetite and behavior changes.

Limits and cautions

• Dates are estimates based on research averages. Follow your vet's exam for pregnancy confirmation and birth decisions.
• The mating-date calculation assumes mating and ovulation happened close together. If fertilization actually came a few days later, the calendar's weeks and schedule shift by the same amount.
• Breed averages come from a survey of UK pedigree cats. For mixed breeds or breeds not in the table, the overall average of 65 days is used.
• The accuracy of ultrasound formulas depends on the timing and the size of the cat, and drops sharply just before birth. The Maine Coon formula is not used.
• The dates and values you enter are calculated only in your browser and are not sent to a server. If you press "Copy link", those values are put into the address.

Sources

• 01Holst BS (2022), Feline breeding and pregnancy management: What is normal and when to interveneJ Feline Med Surg. Average about 65 days (57-72), 95-97% at 61-70 days, sac at day 10, heartbeat at days 16-17, palpation at 21-25, relaxin at day 29, C-section advised at 71 days after mating, ICC and BP formulas
• 02Sparkes AH et al. (2006), A questionnaire-based study of gestation, parturition and neonatal mortality in pedigree breeding cats in the UKJ Feline Med Surg. 1,056 litters, average 65.1±2.2 days, 90.2% at 63-67 days and 97.1% at 61-69 days, breed averages (table 1), 4.6 kittens, C-section 8.0%
• 03Root Kustritz MV (2006), Clinical management of pregnancy in catsTheriogenology. Average 65.6 days (52-74), Siamese 63 days and Persian 65 days cited, average 4.0 kittens
• 04Beccaglia M et al. (2016), Determination of gestational time and prediction of parturition in dogs and cats: an updateReprod Domest Anim. Formulas that predict the birth date from ultrasound measurements (cited in Holst 2022)
• 05Keiser R et al. (2017), Are foetal ultrasonographic and maternal blood progesterone measurements near parturition reliable predictors of the time of birth in the domestic cat?Reprod Domest Anim. Hit rate for measurements within 5 days of birth: head width 27-53%, body diameter 17-35%
• 06Socha P, Janowski T (2019), Development of specific fetometric formulas of ICC and BP for predicting the parturition date in Maine Coon queensReprod Domest Anim. Maine Coon specific ICC and BP formulas
• 07Merck Veterinary Manual: Pregnancy Determination in Bitches and QueensFeline ultrasound formulas after day 40 (25 × BP + 3, 11 × BD + 21, in cm), error ±2 days, days to birth = 61 - estimated day, implantation at day 14
• 08Merck Veterinary Manual (owner edition): Management of Reproduction of CatsConfirm at days 21-30, X-ray to count kittens after day 55, 25% more food in the last 3 weeks, kitten food, no supplements, birth 64-66 days after mating
• 09VCA Animal Hospitals: Pregnancy and Parturition in Cats60-67 days (average 63-65), X-ray at about day 45, below 100 °F in the last 24 hours, nesting in the last week, 20 minutes, 10 minutes, 103 °F and bleeding criteria
• 10Cats Protection: Pregnant cats, birth and care of young kittens (EG18)Pinking up at weeks 3-4, birthing spot by 2 weeks before the due date, 5-30 minutes per kitten with 10-60 minutes between, 30 minutes of straining, 1 hour and green discharge criteria
• 11International Cat Care: Cat pregnancy63-65 days, pink enlarged nipples as the first sign, nesting in the last 2 weeks, kitten food
• 12Beccaglia M, Luvoni GC (2012), Prediction of parturition in dogs and cats: accuracy at different gestational agesReprod Domest Anim. Dog and cat scans pooled: ICC in weeks 4-5 within ±2 days 93.1% and 85.9%, BP in weeks 5-8 82.3-95.2%, week 9 69.8%

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