Livestock Gestation & Due Date Calculator
Expected calving, lambing, kidding, farrowing, foaling and whelping dates from the breeding date — or the birth season from the dates the male went in and came out, or the breeding date for a target birth date. Gestation by species, the normal window, pregnancy-check, vaccination, feeding and dry-off dates, and births by heat cycle.
How it works
Due date = breeding date + average gestation for the species (cow 283, ewe 147, goat 150, sow 114, mare 340, jenny 365, alpaca 345, buffalo 310, bitch 63, queen 65, rabbit 31, guinea pig 66 days) · window = breeding date + breed-typical range · season = (male in + gestation) to (male out + gestation) · breed on = wanted birth date − gestation · late-pregnancy feeding = due date − 30% of gestation
Gestation length is remarkably consistent within a species — a sow farrows 114 days after service almost to the day, the classic “three months, three weeks and three days” — but varies a little by breed, litter size and the sex of the offspring: a 2024 study of AI-bred beef cows averaged 280 days rather than the traditional 283, Herefords run a few days longer than Angus, and mares range from 320 to 360 days. Working from the service or AI date gives the expected date and the window in which to watch; from that date the calculator counts the pregnancy checks, vaccinations that need to be given 3–6 weeks before birth so colostrum carries antibodies, the feed increase for late pregnancy when most foetal growth happens, and drying off dairy animals. With natural service over several weeks, the birth-season mode uses the dates the male went in and came out and splits the season by heat cycle, and the when-to-breed mode counts back from the birth date you want. Enter your own gestation length to use a herd or breed average. Dates are counted in whole calendar days, so they do not shift with the time zone.
Worked example
A cow served on Thursday, October 1, 2026 is due to calve 283 days later, on Sunday, July 11, 2027, with a normal window from July 3 to July 20 (days 275–292). Pregnancy can be confirmed by ultrasound from October 29, a dairy cow should be dried off on May 12, 2027, and her late-pregnancy ration starts on April 17, 2027. With the bull in from October 1 to November 11 instead, calves are due from July 11 to August 21, 2027.
Sources: Hay & Forage Grower — gestation length in Angus, Hereford and Shorthorn cattle (2024 J. Anim. Sci. data) · Drovers — is 283 days the accurate average gestation length? · Calculator Soup — gestation periods by animal
Frequently asked questions
Which date do I use with a bull or ram running with the herd?
Choose “Birth season” and enter the day the male went in and the day he came out. The expected births then run from (in date + gestation) to (out date + gestation), split by heat cycle so you can see how many should come early. Raddle or crayon harnesses narrow individual dates.
Do twins or heifers change the date?
Twins and female offspring tend to come a day or two earlier; first-calf heifers slightly earlier than mature cows; bull calves and some breeds (e.g. Brahman) later. A large study of AI-bred beef cows found bull calves carried about 1.2 days longer than heifer calves.
How many days is a cow pregnant?
The traditional figure is 283 days, a little over nine months, with a normal range of about 275 to 292 days. Modern AI-bred beef herds average closer to 280 days. Use the own-gestation field for your herd’s average.
How do I plan for births on a certain date?
Choose “When to breed” and enter the birth date you want: the calculator subtracts the gestation length and shows the breeding window that gives births around that day, plus a two-cycle window for putting the male in.
How long is a sow pregnant?
114 days on average — three months, three weeks and three days — with most litters between 112 and 116 days.
Related calculators
Farm planning estimate. Breeds, climate, feed quality and local extension guidance change the numbers — use this to plan, and your own records to manage.