How Long Is a Horse Pregnant? Mare Gestation in Days and Months
A horse is pregnant for about 340 days, which is roughly 11 months. The normal range is unusually wide: many mares foal anywhere between 320 and 370 days and everything is fine. Miniature horses often foal a few days earlier, and donkeys carry closer to a full year.
Horse gestation in days and months
| Type | Average gestation | In months |
|---|---|---|
| Horse (most breeds) | about 340 days | about 11 months |
| Pony | about 330-340 days | about 11 months |
| Miniature horse | about 330 days | about 11 months |
| Donkey (jenny) | about 365 days | about 12 months |
| Normal range, any horse | 320-370 days | 10.5-12 months |
People usually say "11 months" because 340 days is 11 months and about 5 days. A mare covered on 1 May would be due around 6 April the following year.
Why the window is so wide
Most livestock gestation lengths sit tightly around an average. Mares are the exception: a healthy mare can foal anywhere from about 320 to 370 days after her last cover, a 50-day spread, and still be completely normal. Four things push a mare toward one end of it:
- Time of year she was bred. Mares bred early in the year, while days are still short, commonly carry longer than mares bred in late spring and summer. The foal seems to wait for grass and warmth.
- The foal's sex. Colts are often carried a few days longer than fillies.
- The mare herself. Many mares repeat their own pattern within a few days every year. Your own notes from her last foaling beat any average in a book.
- Condition and age. Thin mares and very old mares tend to be less predictable.
Month by month
| Stage | What is happening | What you do |
|---|---|---|
| Days 14-16 | The embryo is visible on ultrasound. | First vet check. This is when twins are found and managed, which matters: twins rarely end well in horses. |
| Days 25-30 | A heartbeat can be seen. | Confirm the pregnancy. |
| Months 2-3 | Early loss risk falls after about day 45. | A recheck around day 45 confirms it is holding. |
| Months 4-7 | Slow, steady growth. The mare barely looks pregnant. | Normal work and normal feeding. Keep up deworming and farrier visits. |
| Months 8-9 | About 60% of the foal's growth happens in the last three months. | Raise feed quality. Ask your vet about pre-foaling vaccines, usually 4-6 weeks out. |
| Month 10 | The udder starts to fill, often first at night. | Move her to where she will foal so she builds antibodies to that environment. |
| Last 2 weeks | Udder full, teats point down, muscles beside the tail soften. | Foaling watch. Wax on the teats often means foaling within 24-48 hours. |
How to work out your mare's foaling date
Add 340 days to the last cover or insemination date. If she ran with a stallion, use the day they were separated as well, so your window covers every possible day. The mare gestation calculator does this and adds the vet-check dates above; the 340-day foaling chart gives the same thing as a printable page for the barn wall.
Foaling, and when to call the vet
Foaling itself is fast. Stage one, restlessness and sweating, can last a few hours. Stage two, the actual delivery, is usually over in 20 to 30 minutes, and both front feet should appear first with the nose resting on them. Stage three, passing the placenta, should finish within about three hours.
Call your vet straight away if: delivery has not progressed within about 20 minutes of the water breaking; you see a red velvety bag instead of the white sac (a "red bag" delivery); only one foot or a head appears; the placenta has not passed within three hours; or the foal is not standing and nursing within a couple of hours of birth.
A mare past 340 days is not an emergency on her own. Past 370 days, or any discharge, colic or illness at any stage, is a reason to call.
Common questions
How many months is a horse pregnant?
About 11 months. The average is 340 days, and anything from 320 to 370 days is a normal pregnancy.
Can a horse be pregnant for 12 months?
Yes. Gestations past 365 days happen and usually produce a normal foal. Donkeys average about 12 months anyway. Talk to your vet if she goes past 370 days or seems unwell.
What are the signs a mare is close to foaling?
The udder fills in the last few weeks, wax appears on the teats (often 24-48 hours before), and the muscles beside the tailhead soften. Many mares foal at night.
When can you tell if a mare is pregnant?
A vet can usually see the pregnancy on ultrasound from about day 14, which is also the best time to find twins.
Do mares foal early or late?
Both are common, because the normal range is wide. A foal born before about 320 days is premature and needs veterinary help straight away.
Figures are typical values from university extension and breed-association guidance. Estimates only. Individual animals vary — confirm pregnancy and health questions with your veterinarian.