How Long Is a Horse Pregnant? Mare Gestation Explained
A horse is pregnant for about 340 days, roughly 11 months. The normal range is unusually wide: many mares foal anywhere from 320 to 370 days. Miniature horses often foal a few days earlier, and donkeys carry closer to a full year.
Horse gestation at a glance
| Type | Average gestation |
|---|---|
| Average horse | about 340 days |
| Miniature horse | about 330 days |
| Donkey / jenny | about 365 days |
Why the window is so wide
Most livestock gestation lengths cluster tightly around an average, but mares are the exception. A healthy mare can foal anywhere from about 320 to 370 days after breeding, a 50-day spread, and still be considered completely normal. Daylight length, the mare's condition, and simply her own individual pattern all play a part. Many mares repeat their own timing within a few days from year to year, so a mare's own foaling history is often a better guide than the herd average.
A timeline of vet checks
- Day 14–16: first ultrasound check. This is also when a vet looks for twins, which are risky in horses and are usually reduced to one embryo.
- Day 25–30: a heartbeat is usually visible on ultrasound.
- Day 45: a recheck to confirm the pregnancy is holding.
- 4–6 weeks before foaling: ask your vet about pre-foaling vaccines, timed to boost antibodies in the mare's first milk (colostrum).
- Last 2 weeks: foaling watch begins: the udder fills, wax appears on the teats (often 24–48 hours before foaling), and the muscles around the tailhead relax.
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 for a period, add the day they were separated so the window covers every possible foaling day. The calculator below applies the wider 320–370 day range, adds the vet-check dates above, and lets you keep notes for each mare from year to year.
Common questions
How many months is a horse pregnant?
About 11 months, or 340 days on average, though anywhere from 320 to 370 days is considered a normal pregnancy.
What are the signs a mare is close to foaling?
Udder filling in the last few weeks, waxing (small drops of colostrum on the teats, often 24–48 hours out), and a relaxed, softened area around the tailhead.
Figures are typical values from university extension and breed-association guidance. Estimates only. Individual animals vary — confirm pregnancy and health questions with your veterinarian.