Foaling & Gestation
Foaling Date Calculator
Turn a breeding date into an estimated foaling date and window.
Enter the breeding date to see the estimated foaling date, window and countdown.
What this tool does
Enter the date a mare was bred and get her estimated foaling date, the normal 320 to 370 day window, a live countdown, and a foal-watch checklist keyed to the days of gestation. Mare gestation averages about 340 days, roughly eleven months, but it is unusually variable, so the tool shows the window, not just a single date.
How to use it
- Enter the breeding date. Type or pick the date the mare was bred or covered.
- Read the due date and window. The tool shows the 340-day estimated due date and the normal 320 to 370 day window.
- Plan foal watch. Use the countdown and the day-by-day checklist to schedule vet checks, vaccinations and foal watch.
Frequently asked questions
How long are horses pregnant?
A mare's gestation averages about 340 days (roughly 11 months), but the normal range is wide, about 320 to 370 days. Mare gestation is one of the most variable among domestic animals, so the due date is a target, not a guarantee.
How is the foaling date calculated?
The tool adds 340 days to the breeding (cover) date for the estimated due date, and marks the normal window from 320 to 370 days after cover. It also counts the days remaining and flags which trimester the mare is in.
When should I start foal watch?
Foal watch generally begins around day 320, when the normal window opens. Move the mare to her foaling stall or paddock, watch for udder development and waxing, and be ready. Many mares foal within a couple of weeks either side of the 340-day average.
Is a foal born at 320 days premature?
Foals born before about 320 days are generally considered premature and may need veterinary support; those before roughly 300 days rarely survive. If your mare shows signs of foaling well before the window opens, call your veterinarian.
Do colts and fillies have different gestation lengths?
On average colts are carried slightly longer than fillies, often a few days, but the difference is small next to the normal variation between mares, so it does not change the planning window meaningfully.