Add a typical mare gestation (default 340 days) to the last breeding or ovulation date to plan foaling — or count back from the month you want foals.
Use this after a cover, AI, or confirmed ovulation date to plan vaccinations, a foaling-stall move, and foal-watch nights.
Mare gestation commonly runs about 320–360 days, with 340 a widely used planning figure. Individual mares tend to repeat their own length, so past records beat the average.
Forward mode adds gestation days to the breeding date. Reverse mode subtracts gestation days from the date you want mares to foal. The 340-day default is a common planning figure; enter your mare’s own history if you have it.
foaling_date = breeding_date + gestation_days
breeding_date = target_foaling_date − gestation_days
window = result ± window_days
Bred 1 May 2026 at 340 days → due about 6 Apr 2027. With a ±10 day window, watch roughly 27 Mar 2027 – 16 Apr 2027.
Reverse check: to have mares foal on 6 Apr 2027, breed on 1 May 2026 (6 Apr 2027 − 340 days).
Assumptions: calendar-day arithmetic from a single breeding date; gestation length is a planning average you can change.
Limits: Normal mare gestation varies widely, and a single average can be off by weeks. Not a pregnancy diagnosis and not veterinary advice.
Responsibility: confirm pregnancy with your veterinarian and have facilities and supplies ready before the early edge of the window.
Horses have a broad normal gestation range. Many mares foal well before or after day 340 and are still normal, so a ±10 day or wider watch window is realistic.
Use the confirmed ovulation date if your veterinarian recorded one; otherwise use the last cover or AI date.
Donkey gestation is usually longer, often around 12 months or more. Enter the length your veterinarian or breed guide gives.