A mare carries her foal for about 340 days, close to 11 months, with a normal range of 320 to 370 days. That range is the widest of any common farm animal, which is exactly why horse owners track the pregnancy month by month instead of circling a single due date. This guide walks all 11 months: the early ultrasound checks, the quiet middle stretch, and the foaling watch that begins at day 320.
To turn month 11 into actual dates on your calendar, enter the breeding date in our horse gestation calculator or the mare gestation calculator for a mare specific due date with the full 320 to 370 day window.
Need the full picture? This page is the month by month timeline you can scan between barn chores. For breed-by-breed gestation lengths, the twin problem in detail, and complete foaling preparation, read our complete horse gestation guide.
11-Month Pregnancy at a Glance
M1-3
M4-6
M7-8
M9-10
M11
Months 1 to 3
Confirm & twin check
Months 4 to 6
Quiet growth
Months 7 to 8
Belly grows
Months 9 to 10
Vaccines, udder
Month 11
Foaling watch
The 340-Day Timeline by Month
| Months | Days | What Happens | What to Do |
|---|---|---|---|
| Months 1 to 3 | Days 1 to 90 | The embryo implants and a heartbeat becomes visible on ultrasound. Twins, if any, are visible now, and twins rarely end well without intervention. | Ultrasound at day 14 to 16 to confirm pregnancy and check for twins, then a recheck around day 45 to confirm the heartbeat and a properly developing fetus. |
| Months 4 to 6 | Days 91 to 180 | The middle months are quiet. The fetus grows slowly, the mare's shape changes little, and she may look completely normal. | Feed a balanced maintenance diet with good forage. Light riding is fine for most mares with your vet's sign off. |
| Months 7 to 8 | Days 181 to 240 | The belly drops and rounds out, and weight gain becomes obvious even to visitors. The foal starts its biggest growth phase. | Watch body condition and adjust feed slowly. This is when structured monitoring routines should begin. |
| Months 9 to 10 | Days 241 to 300 | The foal packs on most of its final size. Udder development begins near day 300, the first visible sign that the countdown is real. | Ask your vet about vaccinating in the final 60 days so the mare loads her colostrum with antibodies for the foal. Raise feed energy gradually. |
| Month 11 | Days 301 to 340 | Average gestation ends at day 340. The udder swells, the nipples may wax, and the muscles and ligaments around the tail head soften as foaling approaches. | Watch from day 320, day and night. A red velvety sac instead of a white one at the vulva is a red bag delivery: call the vet immediately. |
The Final Month Watch List
Four signs tell you the foal is on the way. The udder fills and firms over the last 2 to 4 weeks. The muscles and ligaments on either side of the tail head soften and sink, usually in the final week. The vulva lengthens and relaxes. And the nipples develop waxy beads of colostrum, which typically appear 24 to 48 hours before foaling. When several of these show up together, the foal is close even if the calendar says day 340 is still days away.
Because the normal range runs all the way to day 370, do not wait for a due date to start watching. Night checks begin at day 320, since most mares foal between dusk and dawn. Our horse foaling calculator gives you the exact day to start, and our guide to horse pregnancy signs covers the changes month by month in more detail.
Feeding Changes Across the 11 Months
For the first two thirds of pregnancy the mare needs little more than a good maintenance diet: quality forage, a balanced vitamin and mineral supplement, and clean water. Overfeeding early just adds fat, and fat mares foal harder. The fetus demands real nutrition late: from roughly month 9 onward, increase energy and protein gradually, and in the final months split concentrates into smaller meals since a full uterus leaves less room for a big feed. Aim for steady condition rather than big swings, and make every ration change over a week or more.
Emergency Thresholds: Red Bag and More
The red bag delivery is the one to memorize. If a dark red, velvety sac appears at the vulva instead of the normal translucent white membrane, the placenta has detached early and the foal is being starved of oxygen. Call the vet immediately and be ready to open the sac and pull the foal yourself if help cannot arrive within minutes. Two other thresholds matter almost as much: no foal within 20 to 30 minutes of the water breaking, or visible hooves with no nose alongside them, both mean call now, not in an hour. After foaling, a placenta that has not passed within about 3 hours also needs a veterinary call.
Planning a breeding rather than following a pregnancy? The horse breeding hub collects the season tools, and printables has foaling checklists you can post in the barn. For breed level differences in gestation length and the full biology, see the complete horse gestation guide.
Sources & References
- Merck Veterinary Manual: Equine reproduction and foaling management
- Cornell University College of Veterinary Medicine: Mare gestation and twin reduction
- University of Minnesota Extension: Horse breeding and pregnant mare nutrition
- American Association of Equine Practitioners: Foaling and red bag delivery guidelines