Calculate equine foaling dates and track pregnancy milestones by breed. Covers the 320-370 day gestation with veterinary checkpoints and foaling preparation.
Equine gestation averages 340 days (approximately 11 months), with a normal range of 320-370 days — one of the longest and most variable gestations among domestic animals. This extended pregnancy produces a highly developed foal that can stand and nurse within hours of birth. Breed, foal sex, season, nutrition, and individual variation all influence gestation length — colts tend to be carried 2-7 days longer than fillies, and mares bred later in the season may carry slightly shorter.
Proper management of the 11-month pregnancy requires careful attention to veterinary checkpoints: pregnancy confirmation at 14-16 days, fetal sexing at 60-65 days, rhinopneumonitis vaccinations at months 5, 7, and 9, and pre-foaling preparation in the final 2-4 weeks. Approximately 85% of foals are delivered at night, and most healthy foalings complete within 30 minutes of active labor.
This calculator provides breed-adjusted foaling date predictions, tracks pregnancy through trimesters, and maps critical veterinary and management milestones throughout the 11-month journey from breeding to birth.
With an 11-month pregnancy requiring multiple timed vaccinations, veterinary checks, and a narrow window for foaling preparation, precise date tracking is essential. Even experienced breeders benefit from automated milestone calculations across such a long gestation. This horse gestation calculator helps you compare outcomes quickly and reduce avoidable mistakes when making day-to-day care decisions. Use the estimate as a planning baseline and confirm final decisions with a qualified professional when risk is high.
Due Date = Breeding Date + Breed Average Gestation. Averages: Light breeds (Thoroughbred, Arabian) 335-340 days; Warmblood 340-345 days; Draft breeds 340-350 days; Ponies 335-340 days; Miniature horses 320-335 days. Adjustments: Colt foals +2-7 days, Filly foals baseline, Maiden mares +5-10 days common. Rhinopneumonitis vaccines: months 5, 7, 9. Foaling watch begins: day 320.
Result: Expected foaling: ~March 6, 2026 (day 340). Rhinopneumonitis: Aug 29, Oct 28, Dec 27.
A Thoroughbred mare bred April 1 has an expected foaling date around March 6 (340 days). Key milestones: pregnancy check at day 14-16, fetal sexing possible at day 60-65, rhinopneumonitis vaccines at months 5/7/9, foaling watch from day 320 (Feb 14). Most Thoroughbreds foal between days 330-345.
**Trimester 1 (Days 1-110):** Embryo development, fixation, and organogenesis. Critical period for twin management — twins must be reduced before day 16 for best success. Pregnancy check at 14-16 days, recheck at 25-30 days. Minimal dietary changes needed; maintain normal exercise. **Trimester 2 (Days 111-225):** Fetal growth accelerating. Fetal sexing possible at 60-65 days via ultrasound. Begin rhinopneumonitis vaccination schedule. Normal exercise and turnout continue. Light increase in nutrition quality. **Trimester 3 (Days 226-340+):** Rapid fetal growth — the fetus gains 60% of its birth weight in the last 90 days. Significant dietary increase required (especially last 60 days). Reduce strenuous exercise. Prepare foaling area. Begin udder observation. Final rhinopneumonitis vaccine at month 9.
**Stage 1 (1-4 hours):** Restlessness, sweating, pawing, looking at flanks, frequent urination. The mare is experiencing contractions positioning the foal. **Stage 2 (15-30 minutes):** Active delivery. Water breaks, followed by appearance of front feet (soles down) and nose. Most foals are delivered within 20-30 minutes. If no progress within 20 minutes of active pushing, call the vet immediately. **Stage 3 (1-3 hours):** Placenta passage. The entire placenta should pass within 3 hours. A retained placenta is a medical emergency in horses — call the vet if not passed by 3 hours.
Unlike many species, twin pregnancy in horses is dangerous — the equine uterus cannot adequately support two foals, frequently resulting in abortion of both around months 7-9, or the birth of two weak, undersized foals. Veterinary reduction of one twin (by crushing the embryonic vesicle) before day 16 has the best success rate. This is why the day 14-16 ultrasound is so critical.
Average 340 days (about 11 months), with a normal range of 320-370 days. This extreme variation is normal — a mare foaling at day 325 or day 355 may both be perfectly healthy. Gestation under 320 days is considered premature, and foals may need neonatal intensive care.
Multiple factors contribute: breed (draft breeds carry longer), foal sex (colts 2-7 days longer), season of breeding (late-season mares may carry shorter), nutrition, individual genetics, and even weather patterns. Mares seem to have some control over foaling timing, often delaying until conditions feel safe.
Approximately 85% of foaling occurs between 10 PM and 2 AM. This is believed to be an evolutionary adaptation — foaling under cover of darkness and having the foal mobile by dawn reduced predation risk. This makes overnight foaling surveillance important.
Equine herpesvirus (EHV) rhinopneumonitis vaccines should be given at months 5, 7, and 9 of pregnancy to prevent virus-induced abortion. This is one of the most critical preventive measures in equine pregnancy management.
Begin observing the mare closely from day 320 onward. Physical signs of approaching foaling: udder development ("bagging up") 2-4 weeks before, waxing of teats (yellowish droplets) 24-48 hours before, relaxation of vulva and tailhead muscles, restlessness and sweating.
A red bag (premature placental separation) is an emergency where the cherry-red chorioallantois presents first instead of the normal translucent white amnion. The placenta must be immediately torn open to allow the foal to breathe. Without intervention, the foal suffocates within minutes.