Use our free horse gestation calculator to find your mare’s due date, track week-by-week pregnancy milestones, and prepare for foaling. Covers horse gestation period, signs of imminent foaling, and a complete pregnancy timeline from breeding to birth.
Horse Due Date Calculator
The average horse gestation period is 335–345 days (approximately 11 months), with a normal range of 320–370 days.
Due Date Formula: Breeding Date + 340 days = Estimated Foaling Date
| Breeding Month | Due Date (340 days) | Earliest (320 days) | Latest (370 days) |
|---|---|---|---|
| January 1 | December 7 | November 17 | January 6 |
| February 1 | January 7 | December 18 | February 6 |
| March 1 | February 5 | January 16 | March 7 |
| April 1 | March 7 | February 15 | April 6 |
| May 1 | April 6 | March 17 | May 6 |
| June 1 | May 7 | April 17 | June 6 |
Horse Pregnancy Week-by-Week Timeline
| Stage | Timing | Key Milestones | Action Required |
|---|---|---|---|
| Embryo detection | Days 14–16 | Embryo visible on ultrasound | Confirm pregnancy; check for twins |
| Heartbeat | Days 24–26 | Fetal heartbeat detectable | Confirm single viable pregnancy |
| Months 4–6 | Days 90–180 | Rapid growth; fetal movement begins ~Month 5 | Core vaccines at Month 5 (EHV-1) |
| Months 8–10 | Days 210–300 | Foal gains 60% of birth weight in final trimester | Vaccinate mare; increase feed 20–30% |
| Pre-foaling | Days 300–320 | Udder develops; waxing 24–48h before foaling | Set up foaling stall; begin nightly checks |
| Foaling | Days 320–370 | Stage 1 (1–4h) → Stage 2 (20–30 min) → Stage 3 (1–3h) | Be present; call vet if Stage 2 > 30 minutes |
Signs of Imminent Foaling
| Sign | Timing Before Foaling | Notes |
|---|---|---|
| Udder filling (bagging up) | 2–6 weeks before | Gradual; maiden mares may bag up later |
| Muscle relaxation around tailhead | 1–2 weeks before | Rump appears “sunken” as ligaments soften |
| Vulva elongation | Days to hours before | Vulva appears longer and looser |
| Waxing (colostrum droplets) | 24–48 hours before | Most reliable sign; not all mares wax |
| Milk streaming | Hours to imminent | Collect colostrum if streaming — reduces foal immunity |
| Restlessness, pacing | Hours to imminent | Stage 1 labour; can last 1–4 hours |
| Water breaking | Imminent (Stage 2) | Foal should arrive within 20–30 minutes |
The 1-2-3 Rule for Newborn Foals
After foaling, use the 1-2-3 Rule to assess whether your foal is healthy:
- 1 hour: Foal should stand within 1 hour of birth
- 2 hours: Foal should nurse (find and latch onto the teat) within 2 hours
- 3 hours: Mare should pass the placenta within 3 hours — a retained placenta after 3 hours is a veterinary emergency
A foal not nursing within 3 hours means it cannot absorb antibodies from colostrum — call your vet immediately.
Mare Nutrition During Pregnancy
| Trimester | Feed Increase | Key Nutrients |
|---|---|---|
| First (Months 1–5) | None | Quality forage; baseline vitamins/minerals |
| Second (Months 5–8) | +10–15% | Increase energy and protein |
| Third (Months 8–birth) | +20–30% | Protein (lysine), calcium, phosphorus, vitamin E, omega-3 |
| Lactation (peak) | +50–75% | Highest demand of a mare’s life |
Frequently Asked Questions
How long is a horse pregnant?
The average horse gestation period is 335–345 days, with a normal range of 320–370 days. Most mares foal between 330 and 345 days. Foals born before Day 300 are premature; those after Day 360 are post-term but often develop normally if the mare is healthy.
How do I calculate my mare’s due date?
Add 340 days to your mare’s breeding date. Alternatively, add 11 months and 5 days. Individual mares often have a consistent gestation length across pregnancies — if you know her history, use that as your guide.
What is waxing in a mare?
Waxing refers to small droplets of colostrum (first milk) that appear on a mare’s teats, typically 12–48 hours before foaling. It is one of the most reliable pre-foaling signs, though not all mares show obvious waxing. Begin foaling watch immediately when waxing appears.
When should I call a vet during foaling?
Call your vet immediately if: the water breaks and no foal appears within 30 minutes; a red bag appears at the vulva (premature placental separation — emergency); the foal is not standing within 2 hours; the mare has not passed the placenta within 3 hours of foaling.
Can horse gestation be shorter than 320 days?
Foals born before Day 300 are classified as premature with immature organ systems, particularly the lungs. They require intensive veterinary care. Foals born between Day 300 and 320 are early term — many survive but may need extra support. Always have your vet assess any foal born before Day 320.