How long is a horse pregnant?
The Merck Veterinary Manual says "Horses have an average pregnancy length of about 340 days (about 11 months)." Individual mares vary a lot. Published normal ranges differ between sources: Dr Michelle LeBlanc, a reproduction specialist writing in The Horse, gives "325 to 360 days", and an extension specialist quoted by the same magazine puts the average at about 335 to 345 days.
The calculator uses 340 days and shows a wide window from day 320 to day 370, so that a normal early or late foal does not fall outside it. The window is a planning aid, not a medical limit: ask your vet what is normal for your mare, especially if she has foaled before.
Window shown = first breeding + 320 days to last breeding + 370 days
Example: bred on 1 January 2026
| Line | Date |
|---|---|
| Start of the window (day 320) | 17 November 2026 |
| Expected foaling date (day 340) | 7 December 2026 |
| End of the window (day 370) | 6 January 2027 |
| Have the foaling area ready by | 3 November 2026 |
Pregnancy checks
The Merck Veterinary Manual lists a suggested schedule of veterinary checks, which varies by farm:
| When | What the vet checks |
|---|---|
| Days 14–18 | Pregnancy and twins, by ultrasound. |
| Days 25–30 | Normal embryo development (a heartbeat is present at 24–25 days) and a second check for twins. |
| Days 40–60 | Normal fetal development. |
| Fall check | Confirms the mare is still pregnant. |
Signs that foaling is close
- Udder development. Merck: "The mammary glands (udder) start developing 2 to 4 weeks before foaling."
- Waxing. Wax-like beads on the teats develop "in almost all mares 6 to 48 hours before foaling".
Labour and when to call the vet
From the Merck Veterinary Manual's guide for horse owners:
- The first stage of labour "typically lasts 1 to 2 hours".
- Once the membranes rupture, "an uncomplicated labor usually takes no more than 30 minutes".
- If significant progress is not made within 10 to 15 minutes, call your veterinarian. If the delivery takes more than 30 minutes, call immediately.
- The afterbirth is normally passed within 3 hours of the birth.
This is an estimate, not veterinary advice. Ask your vet to confirm the pregnancy and to tell you when to call during foaling. Keep their emergency number at the stable before the window starts.
Other animals: breeding calculator for dogs, cats, goats, sheep, pigs, cows and rabbits.
Frequently asked questions
How long is a horse pregnant?
About 340 days, or about 11 months, on average according to the Merck Veterinary Manual. Healthy mares often foal earlier or later than the average date.
How do I work out my mare's due date?
Add 340 days to the breeding date. A mare bred on 1 January 2026 is due around 7 December 2026. If she was bred over several days, use the first date.
When can a vet confirm a mare is pregnant?
The Merck Veterinary Manual's suggested schedule starts with an ultrasound check for pregnancy and twins at days 14 to 18, repeated at days 25 to 30.
What are the signs a mare is about to foal?
The udder starts developing 2 to 4 weeks before foaling, and wax-like beads appear on the teats in almost all mares 6 to 48 hours before.
How long does foaling take?
Merck says the first stage typically lasts 1 to 2 hours, and an uncomplicated delivery usually takes no more than 30 minutes after the membranes rupture. Call your vet immediately if it takes longer.
Sources
Merck Veterinary Manual: Management of reproduction in horses · Merck Veterinary Manual: Pregnancy determination in horses · The Horse: Long gestations (M. LeBlanc, DVM)
Last reviewed: November 2026 · By Muhammad Shujah Uddin Qazi · How we check rates · Fee changes tracker