Foaling date calculator
Mares carry for about 340 days, but anything from 320 to 370 is normal. Enter the last breeding (or ovulation) date for the due date, the foaling window, and a dated calendar of everything to do along the way.
Due date
- Foaling window
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- Days pregnant today
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How long is a mare pregnant?
Normal window: 320 to 370 days
The average is about 340 days (11 months), but healthy foals are born anywhere from 320 to 370 days. Mares bred early in the year tend to carry longer; colts often come a few days later than fillies. A foal born before 300 days is considered premature and needs a vet right away.
The calendar
The first ultrasound at 14–16 days confirms pregnancy and catches twins, which rarely survive to term. EHV-1 (rhinopneumonitis) vaccines at months 5, 7 and 9 protect against virus-caused abortion, and core vaccines 4–6 weeks before foaling pass immunity to the foal through the first milk. These follow the American Association of Equine Practitioners' vaccination guidelines; your vet will tailor them.
Wondering what color it will be? Try the foal coat color calculator.
Frequently asked questions
Why is the normal window so wide — 320 to 370 days?
Gestation length in mares varies more than in most livestock, influenced by the individual mare, the foal's sex, and even the time of year bred — which is why vets treat the 320–370 day range as normal rather than expecting a single fixed due date.
What if I bred on more than one day?
Use the date of ovulation if you know it (from an ultrasound or vet exam) rather than the breeding date itself, since ovulation timing is what actually starts gestation and gives a more accurate due-date estimate than breeding date alone.
Should I rely on the calendar instead of watching the mare closely as the date nears?
No — the calendar is a planning guide, not a substitute for watching for the mare's own physical signs (udder development, relaxing of the tailhead ligaments) in the final weeks, since individual mares can foal meaningfully earlier or later than their calculated date.
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