Animal Gestation Calculator
The expected birth date for livestock and pets from the breeding date and the species’ average gestation.
Each species carries for a characteristic time — 283 days for a cow, 340 for a mare, about 150 for a ewe or doe, 114 for a sow, 63 for a dog — with a normal spread of a week or so either side.
How the animal gestation calculator works
Each species carries for a characteristic time — 283 days for a cow, 340 for a mare, about 150 for a ewe or doe, 114 for a sow, 63 for a dog — with a normal spread of a week or so either side. Enter the date of service and the calculator adds the average length; the stage rows show how far along the pregnancy is today.
Formula: due date = breeding date + average gestation (days)
Worked examples
| Inputs | Expected birth date | Note |
|---|---|---|
| Cow bred 1 January 2026 | Sun 11 Oct 2026 | Sun 11 Oct 2026 |
| Mare covered 15 March 2026 | Thu 18 Feb 2027 | Thu 18 Feb 2027 |
| Dog mated 10 May 2026 | Sun 12 Jul 2026 | Sun 12 Jul 2026 |
FAQFrequently asked questions
How accurate is the due date?
It uses the species average; individual animals vary by a week or so either side (mares by several weeks), and breed, litter size and season all shift it. Watch for signs of labour from a week before.
What is the gestation period of a cow?
About 283 days — nine months and a week. Dairy breeds average a few days less, some beef breeds a few days more.
What date do I enter for a dog or cat?
The date of mating, or the first mating if there were several. A dog’s 63 days is really counted from ovulation, so a bitch bred a few days early will seem to go over.
Can I use it for people?
Use a pregnancy due-date calculator instead: human pregnancy is dated from the last menstrual period (40 weeks), not from conception, so the arithmetic is different.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- National Human Genome Research Institute — the US genomics research institute
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.