Days 1–60: embryonic period
The embryonic vesicle moves through the uterus until fixation around day 16, which is why the twin check is scheduled then. Endometrial cups form near day 35 and maintain the pregnancy hormonally.
Horse Gestation Period: How Long Is a Horse Pregnant?
A horse is pregnant for about 340 days, roughly 11 months. Normal foaling happens between 320 and 370 days, and a typical litter is 1 foal.
How long is a horse pregnant?
A horse carries her foal for an average of 340 days, or about 11 months. Counting from the breeding date, foaling is normal anywhere from day 320 to day 370.
Key checkpoints across the 340-day horse gestation, measured in days from breeding:
Horse gestation stages, month by month
Days 61–210: mid gestation
Foetal growth is slow and the mare can usually stay on good forage with a balanced mineral supplement. Continue normal exercise and routine hoof and dental care.
Days 211–300: late gestation
The foal gains most of its weight now. Increase energy and protein gradually, and give rotavirus and rhinopneumonitis vaccinations according to your vet's schedule.
Days 301–340: pre-foaling
Move the mare to her foaling environment at least four weeks before the due date so she builds antibodies to that place. Any Caslick suture must be opened well before labour.
Signs a horse is pregnant
- No return to oestrus about 18 to 21 days after breeding
- Ultrasound confirmation from days 14 to 16
- Udder development starting four to six weeks before foaling
- Waxing of the teats, usually 24 to 48 hours before birth
Signs of approaching foaling
- Relaxed croup muscles and a soft, elongated vulva
- Restlessness, pawing, sweating and repeatedly lying down and getting up in the final hours
- Contact your vet if labour stalls, if the animal strains without progress, or if there is abnormal discharge before foaling begins.
What affects horse gestation length
- Mare gestation is unusually variable: 320 to 370 days is all considered normal, so a single due date is only a midpoint.
- Mares bred in late winter or early spring tend to carry a few days longer than mares bred in summer.
- Colts are commonly carried two to seven days longer than fillies.
- Twin pregnancies are dangerous in horses and are usually reduced to a single embryo at the 14 to 16 day ultrasound.
Estimate your horse's foaling date
Enter the breeding date for an estimated foaling date at 340 days.
Estimate a horse due date
Estimated foaling date
Wednesday, 18 August 2027
Earliest
29 Jul 2027
Latest
17 Sept 2027
Horse pregnancy FAQs
How long is a horse pregnant?
A mare is pregnant for about 340 days, roughly 11 months. Anything from 320 to 370 days is considered normal, so the calculated date is a midpoint rather than a deadline.
Why is the foaling date so unpredictable?
Foaling is triggered by foetal maturity rather than a fixed clock. Season, mare age, foal sex and nutrition all shift the date, which is why the normal range spans about seven weeks.
Is a foal born before 320 days viable?
A foal born before about 320 days is premature and needs immediate veterinary care. Survival improves considerably after 330 days, when the lungs and immune transfer are more mature.
When should I check for twins?
Ultrasound at days 14 to 16 is standard. Twin pregnancies rarely produce two healthy foals and often end in late abortion, so one embryo is normally reduced at that scan.
What are the signs foaling is imminent?
Udder filling weeks ahead, waxing of the teats one to two days before, milk that turns opaque and calcium-rich, relaxed tail head and restlessness. Most mares foal at night.
Should I change the mare's feed in late pregnancy?
Yes. From about day 300 the foal's growth is rapid, so increase energy and protein gradually and keep mineral and vitamin intake balanced. Avoid sudden ration changes at any stage.