Animal Gestation Calculator: Cow, Dog & Horse Due Dates

An animal gestation calculator adds the species' typical pregnancy length to the breeding date. Dogs average about 63 days (normal 58–72 from breeding), cats about 65, pigs 114, sheep 147, goats 150, cows 283 and horses about 340 days. It's for breeders, farmers and pet owners: pick the animal, enter the breeding date (or, for dogs, a hormone-timed date) and you get the due date, the normal window and how far along the pregnancy is today.

Every length comes from the Merck Veterinary Manual or a university extension service or veterinary school. It is a planning tool, not a diagnosis: your veterinarian should confirm the pregnancy and help you plan for the birth.

How to use this due date calculator

1. Choose the animal: dog, cat, sheep, goat, pig, cow, horse, rabbit, or llama and alpaca.
2. For a cow, choose the breed: Angus, Hereford, Simmental, Brahman-sired, Holstein and others shift the date by several days.
3. For a dog, choose what you are counting from. The breeding date is the default; pick ovulation, LH surge or diestrus if your vet ran tests.
4. Enter the date. It defaults to today, which is handy if you are planning a breeding.
5. Read the due date, the normal window and the day of pregnancy today. For dogs and cats you also see the next vet checkpoint.
6. Press Share to save the result or send it to your vet or breeder.

How the due date is calculated

Due date = start date + typical gestation (days). The window is start date + the low end and + the high end of the normal range. “Day of pregnancy” is the days from the start date to today.

For dogs, 63 days is the midpoint of Merck's 62–64 days from ovulation. For llamas and alpacas, Merck gives about 342 ± 10 days for camelids and notes alpacas run somewhat shorter, so treat that row as approximate.

Why the start date matters so much in dogs

Dogs are the hardest species to predict from a breeding date. The Merck Veterinary Manual explains that a bitch's estrous behavior doesn't line up closely with ovulation, and semen can stay viable in her reproductive tract for 7 days or more. That is why the range from breeding is a wide 58–72 days. Hormone timing narrows it:

If you plan an elective cesarean, ovulation timing matters: Merck says it can be done safely after 62 days of gestation, but earlier the puppies' lungs may not be ready. Near term, most dogs' rectal temperature drops to about 98.8°F (range 98.1–100°F) 8–24 hours before whelping.

Worked examples

Dog bred on April 10

April 10 + 63 days = June 12, 2026. The normal window runs from June 7, 2026 to June 21, 2026. If a progesterone test put ovulation on April 12, the date becomes June 14, 2026 with a much tighter window of Jun 13 to Jun 15.

Ewe bred on October 15 (lamb gestation)

October 15 + 147 days = March 11, 2027. Breed averages put lambing between Mar 8 and Mar 15. If rams ran with the ewes for several weeks, work out the first and last possible dates and plan for lambing across that whole spread.

Sow bred on June 1 (swine gestation)

June 1 + 114 days = September 23, 2026. Most sows farrow between Sep 19 and Sep 26, so move her to the farrowing area before the early date.

Mare bred on May 20

May 20 + 340 days = April 25, 2027. The normal range is wide, from April 5, 2027 to May 25, 2027, and extension specialists note that many mares follow a similar pattern each year, so her past foaling records are a useful guide.

Due dates for breedings on the first of each month, 2026

Typical due dates for five species bred on the first of each month of 2026, using the typical lengths in the table above (dog counted from the first breeding). Each date sits inside a normal window, which is widest for mares (320–370 days, more than seven weeks); use the calculator for the window and for other dates.

The cow column uses the 283-day figure from University of Nebraska–Lincoln Beef and the Montana State University Extension gestation table. Colts tend to be carried 2–7 days longer than fillies.

Cow gestation calculator: breeds, heifers and calving dates

For cattle, choose the breed in the calculator. The 283-day figure from University of Nebraska–Lincoln Beef is the textbook number, but breeds differ by up to about 12 days, which is almost two weeks of calving-watch planning. The widget then draws a calving-date chart: the expected share of calvings on each day, built from the breed mean and the 4.69-day standard deviation in Kansas State University's Angus data.

Cattle gestation length by breed

Read the MARC figures as sire-breed averages: they are least-squares means for crossbred calves out of Hereford, Angus and composite cows, so they show how much a bull's breed shifts the date. In Cycle VII, calves by Angus and Red Angus sires had shorter gestations than those by Hereford and the four Continental breeds, and Limousin-sired calves were the longest of the Continental group. The Angus row is different: it comes from purebred Angus AI records, and it has been falling. K-State reports gestation shortened by 4.3 days over those two decades through genetic selection, and about 68% of the matings fell within one standard deviation, between roughly 274 and 283 days.

Angus gestation calculator example

A cow bred on May 1 is due February 8, 2027 by the 283-day rule, but the Angus average points to about February 4, 2027, four days sooner. Angus data ranged from 264 to 292 days in total, so have calving help ready from the early end of the window rather than the textbook date. For a Brahman-influenced cow bred the same day, the roughly 291-day average moves the date to about February 16, 2027.

Heifers vs cows

First-calf heifers carry slightly shorter than mature cows. In the K-State Angus data, 2-year-old dams averaged 277.7 days and the figure rose steadily with age to 279.6 days for 8-year-olds. The gap is only about 2 days, but it adds up: heifers bred on May 1 average about February 3, 2027, older cows about February 5, 2027. Heifers also have more calving difficulty, so the earlier date is the one to plan checks around. Calf sex matters too: UNL and the USDA-ARS study both found that bull calves are carried longer than heifer calves.

Breeding to calving table

Expected calving dates for breedings on the 1st and 15th of each month from March to August 2026, the months most spring-calving herds breed in. Bull turnout and pull dates give the first and last possible calving dates for a natural-service season.

Breed averages are rounded to whole days for the dates (Angus 279, Hereford 284). The calculator shows a window of 5 days either side of a breed average, about one standard deviation in the K-State data, so roughly two in three cows should calve inside it. For the typical 283-day setting it keeps UNL's 279–287-day range.

What affects gestation length

• Breed. Finn and other prolific sheep breeds carry for 144–145 days on average, while Rambouillet carry for 150–151 days (Montana State).
• Litter size. Ewes carrying multiples tend to deliver a little sooner. Rabbits with small litters (usually four or fewer) tend to carry longer (Merck).
• Sex of the offspring. Bull calves and colts tend to be carried a little longer; colts by about 2–7 days.
• Season. Mares due in late spring and summer tend to have shorter pregnancies than mares due in January or February.

Pregnancy checks for dogs and cats

The Merck Veterinary Manual says ultrasound is the most useful way to confirm pregnancy and is best done at 25–35 days; before day 21 it can give a false negative. A blood relaxin test can detect pregnancy in dogs after 22–27 days. Fetal skeletons show on X-ray from about day 42–45, and an X-ray after day 55 is the best way to count the litter so you know when birth is complete.

When to see a vet

This calculator is general information, not veterinary advice. Book a vet visit to confirm any pregnancy and to plan nutrition, vaccinations and the birth. Get help right away if labor stalls: for dogs, Merck lists no puppy within 24 hours of the temperature falling below 100°F, strong contractions for more than 1–2 hours without a birth, a rest of more than 4–6 hours, obvious pain, or abnormal discharge. Call your vet too if the due window passes with no signs of labor, or if you see bleeding, a foul discharge or a sick-looking mother at any stage.

Don't give a pregnant or nursing dog any medicine, including antihistamines, without asking your vet first; see the dog Benadryl dosage calculator for why. To count days forward from any date, use the date from today calculator.

Frequently asked questions

Sources & method

• Merck Veterinary Manual — Table: Approximate gestation periods
• Merck Veterinary Manual — Whelping and queening in bitches and queens
• Merck Veterinary Manual — Breeding management of bitches
• Merck Veterinary Manual — Pregnancy determination in bitches and queens
• Merck Veterinary Manual (Dog Owners) — Reproductive disorders of female dogs (dystocia signs)
• Merck Veterinary Manual (Cat Owners) — Management of reproduction of cats
• Montana State University Extension — Sheep reproduction
• Merck Veterinary Manual — Breeding, parturition and common lamb diseases of sheep
• Merck Veterinary Manual — Pregnancy in goats
• Purdue University College of Veterinary Medicine — Your sow is expecting (VA-30-W)
• Penn State Extension — Raising pigs 1: farrowing
• Merck Veterinary Manual — Breeding management of pigs
• University of Nebraska–Lincoln Beef — How long does a cow's pregnancy last?
• USDA-ARS Meat Animal Research Center — Germplasm Evaluation Program Progress Report No. 22 (Cycle VII gestation by sire breed)
• USDA-ARS Meat Animal Research Center — Germplasm Evaluation Program Progress Report No. 20 (Cycle VI, incl. Wagyu)
• Casas, Thallman & Cundiff (2011), J Anim Sci — Birth and weaning traits from Hereford, Angus, Brahman, Boran, Tuli and Belgian Blue sires
• Agerholm et al. (2023), Acta Vet Scand — Holstein gestation length (median 278 d)
• Kansas State University Beef Tips (July 2026) — Understanding gestation length in modern beef cattle
• Montana State University Extension — Rancher's notebook beef gestation table (283 days)
• Merck Veterinary Manual (Horse Owners) — Management of reproduction in horses
• eXtension Horses (Cooperative Extension) — Management of the pregnant mare
• Merck Veterinary Manual — Management of rabbits
• Merck Veterinary Manual — Reproduction of llamas and alpacas

Results are estimates for general information. Found an error? It helps everyone — see our methodology.