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Horse Pregnancy Calculator — Mare Foaling Due Date (340 Days)

When will your mare foal? This calculator estimates foaling date from breeding day using the standard 340-day equine gestation(normal range 320-370 days — colts often gestate slightly longer than fillies), and lays out trimester milestones, vet exam windows for ultrasound and Caslick’s, and a foaling-prep countdown. See the AAEP foaling and newborn-foal guidance for the around-the-clock pre-foaling watch protocol.

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Gestation: 320–370 days (avg 340).

Estimated foaling date
April 21, 2027
Window: April 1, 2027 – May 21, 2027
0%
Day
0 / 340
Week
1
Trimester
1
Day 0T1Day 340
1st trimester
d1–1132nd trimester
d114–2263rd trimester
d227–340
340 days remaining until expected due

Upcoming milestones

  • Early ultrasound
    Confirm pregnancy and check for twins.
    Day 14
    May 30, 2026
  • Heartbeat check
    Ultrasound detects fetal heartbeat.
    Day 25
    June 10, 2026
  • Sex determination window begins
    Ultrasound can start assessing sex.
    Day 45
    June 30, 2026
  • Second trimester begins
    Majority of fetal growth occurs now.
    Day 150
    October 13, 2026
  • Third trimester nutrition
    Increase feed quality; fetus grows rapidly.
    Day 240
    January 11, 2027
  • Begin foaling prep
    Move mare to foaling area, observe udder.
    Day 300
    March 12, 2027
  • Earliest viable foaling
    Foals born before this are premature.
    Day 320
    April 1, 2027
  • Expected foaling
    Typical foaling window.
    Day 340
    April 21, 2027
Dates are estimates. Individual pregnancies vary. Always confirm pregnancy and track milestones with a licensed veterinarian.

Mare pregnancy trimester milestones

Trimester / dayMilestoneVeterinary action
Day 14-16Embryo detectable via ultrasoundConfirm pregnancy + check for twins
Day 25-30Fetal heartbeat visibleSecond ultrasound
Day 60-90Fetal sex can be determinedOptional gender ultrasound
Day 150Pregnancy clearly visible externallyRhinopneumonitis vaccine #1
Day 240Third-trimester nutrition rampIncrease feed 15-20%
Day 300-320Pre-foaling preparationCaslick's removal if applicable
Day 330+Foaling watch begins24-hour monitoring; foaling stall ready
Day 340 (avg)FoalingVet on call

Mare pregnancy terminology

Foaling
Equine term for parturition (giving birth).
Caslick’s operation
Suturing of the vulva to prevent contamination; opened (“removed”) before foaling.
Waxing
Wax-like teat secretion 1-4 days before foaling; classic pre-labor signal.
Red bag delivery
Premature placental separation — visible red membrane; veterinary emergency requiring immediate intervention.

Frequently Asked Questions

How long is a horse pregnancy?

Average mare gestation is 340 days (~11 months), with a normal range of 320–370 days. Thoroughbreds and Warmbloods tend toward 335–342; Drafts toward 345–352; ponies toward 330–340.

When can I confirm pregnancy in a mare?

Ultrasound can confirm pregnancy from day 14–16 and check for twins — critical because twin pregnancies are high-risk and one twin is usually manually 'pinched' for single-pregnancy outcome.

When is the fetal heartbeat detectable?

Fetal heartbeat is visible on ultrasound from day 25. Sex can be determined from day 60–70 with fetal imaging.

How do I know when my mare is close to foaling?

Udder development starts 4–6 weeks before. 'Waxing' of teats (dried colostrum) appears 24–48 hours before foaling. Relaxation of pelvic ligaments, vulvar lengthening, restlessness and sweating all signal imminent labor.

What if my mare is overdue?

Mares often carry 2–4 weeks past the 340-day average — a pregnancy up to 365 days is normal. Consult a vet if past day 370 or if there are other concerning signs.

When can a foal be weaned?

Natural weaning happens around 6–8 months. Managed weaning is typically at 4–6 months for foals in breeding operations. Abrupt weaning is stressful; gradual separation is preferred.

Should I ride a pregnant mare?

Light riding is safe for the first 7–8 months in a healthy mare. Avoid strenuous work, jumping and tight saddles. Stop riding by month 9 (day 270).

Sources & References

  1. [1]
    Mare Gestation Length — Kentucky Equine Research
  2. [2]
    Equine Reproductive Management — Merck Veterinary Manual
  3. [3]