Animal Gestation Calculator

Pick the animal and enter the breeding date. You get the due date, the normal birth window and a calendar of key dates.

Estimated due date

Sun, Oct 11, 2026

Normal window: Oct 7, 2026 to Oct 15, 2026

Today: Not bred yet
Days to go: 283

Pregnancy calendar and key dates

Each date links to its source. Your vet may give different timing for your herd or pet.
Date	Day	What to do or expect
Jan 29, 2026	28	Earliest pregnancy check by ultrasound or blood test [source]
Feb 10, 2026	40	Pregnancy check by rectal palpation is possible [source]
Aug 12, 2026	223	Dairy cows: dry off date for a 60 day dry period [source]
Oct 7, 2026	279	Normal calving window opens: have pens, bedding and supplies ready [source]
Oct 11, 2026	283	Estimated due date [source]
Oct 15, 2026	287	Normal window closes: call your vet if no birth [source]

Check with your vet. These are estimates from average gestation lengths. Your vet can confirm a pregnancy, date it more closely, and tell you when to call for help at birth.

Gestation length by species

Average pregnancy lengths: cow 283 days, horse 340, dog 63, goat 150, sheep 147, pig 114, cat 65, rabbit 31 and alpaca 342. Each has a normal range, shown below. Every figure comes from a university extension service, a veterinary school or the Merck Veterinary Manual.

Average gestation and normal range
Animal	Average	Normal range	Note
Cattle	283 days	279 to 287	Breed and calf sex shift the date a few days. Bull calves tend to be carried longer.
Horse	340 days	320 to 370	The widest range here. Colts tend to be carried 2 to 7 days longer than fillies.
Dog	63 days	58 to 72	Window is 58 to 72 days from breeding but 61 to 65 days from a known ovulation date.
Goat	150 days	145 to 155	Avoid deworming days 20 to 60. The last 6 weeks carry the most risk of pregnancy toxemia.
Sheep	147 days	144 to 152	Start checking ewes 1 to 2 weeks before the first due date.
Pig	114 days	114 to 117	Modern herds now average 115 to 116 days, a bit over the classic 114.
Cat	65 days	61 to 70	Most kittens are born between day 61 and day 70.
Rabbit	31 days	28 to 33	Watch for nest building from day 28.
Alpaca and llama	342 days	332 to 352	Same range for llamas. Alpacas tend to be a little shorter.

Sources: cow UNL Beef; horse Purdue and Nebraska; dog Merck and Cornell; goat Merck; sheep NMSU; pig Missouri and Merck; cat JFMS 2022; rabbit Utah State; alpaca Merck.

What is a gestation calculator?

A gestation calculator adds the average pregnancy length of a species to the breeding date. The result is an estimated due date. A good one also shows the normal range around that date, because few animals give birth on the exact average day.

Which farm animal has the longest pregnancy?

Of the animals on this site, alpacas and llamas are longest at about 342 days, followed by horses at about 340 days. Cows come next at about 283 days. Rabbits are shortest at about 31 days.

How the due date is worked out

Due date equals breeding date plus the average gestation length in days. The start of the window is the breeding date plus the shortest normal length. The end is the breeding date plus the longest normal length. The tool counts real calendar days, so leap years are correct.

Due date = breeding date + average days

Example: a goat bred on January 1, 2026 is due on May 31, 2026 (150 days). Her window runs from May 26 to June 5. We check the math against printed tables from NDSU (cattle) and the University of Missouri (swine).

What the pregnancy calendar includes

Each animal gets the dates that matter for it, each with a link to the source. Examples:

Pregnancy check: cattle by ultrasound from about day 28; pigs from about day 27; cats from day 16 to 17.
Dry off and prep: dairy cows 60 days before calving; mares moved to the foaling area 2 to 3 weeks before.
Birth kit and pens: kidding pens ready when the goat window opens; lambing checks 1 to 2 weeks before.

Calculators for each animal

Questions people ask

Which date should I enter if the male ran with the females?

Enter the first day he was in. That gives the earliest likely birth. Run it again with the day he came out to see when births should end.

How do I add the dates to my phone?

Press Add to calendar. The site saves a small .ics file. Open it and your phone or computer calendar will add each date as an all day event.

Is my data stored?

No. The tool runs in your browser. Your last entry is kept only on your own device so it is there next time.

Why is my vet's date different?

Vets can date a pregnancy by ultrasound or hormone tests. That is more exact than a breeding date. Go with your vet.

References

Approximate Gestation Periods (table). Merck Veterinary Manual.
Whelping and Queening in Bitches and Queens. Merck Veterinary Manual (A. P. Davidson, UC Davis), reviewed June 2025.
Pregnancy in Goats. Merck Veterinary Manual (J. L. Stewart, Virginia Maryland College of Veterinary Medicine), reviewed June 2026.
Breeding Management of Pigs. Merck Veterinary Manual (R. V. Knox, University of Illinois), reviewed July 2026.
Reproduction of Llamas and Alpacas. Merck Veterinary Manual, updated August 2026.
FAQ: Pregnant cows, timing of pregnancy. University of Nebraska Lincoln, UNL Beef.
Calving Book (AS1954), gestation table based on 283 days. North Dakota State University Extension, revised March 2025.
Options for Pregnancy Diagnosis in Beef Cattle. NDSU Agriculture (S. Zoca, University of Tennessee).
How Long Should the Dry Period Be?. Penn State Extension, updated April 2025.
Management of the Pregnant Mare. Extension Horses (K. Anderson, University of Nebraska).
What to Expect When Your Mare is Expecting (VA-26-W). Purdue University Extension.
The normal whelping process. Cornell University College of Veterinary Medicine, Riney Canine Health Center.
Meat Goat Production, Chapter 8: Kidding. Oklahoma State University Extension.
Sheep Production: Birth to Weaning (Circular 703). New Mexico State University, 2022.
Care of Pigs From Farrowing to Weaning (G2500). University of Missouri Extension.
Feline breeding and pregnancy management: What is normal and when to intervene. B. Ström Holst, Journal of Feline Medicine and Surgery, 2022 (PubMed Central).
Rabbit Breeding and Management: A Guide for Producers. Utah State University Extension, July 2025.

Written and checked by the Gestation Calculator team against the sources above. Last updated October 20, 2026. Our method.