Horse Gestation Calculator

Horse pregnancy averages 340 days, or about 11 months, in this calculator. Enter the breeding date to estimate a foaling date and planning window.

Horse gestation at a glance

Average used by this calculator	340 days (about 11.2 months)
Window shown by this calculator	320 to 370 days after breeding
Due date formula	Breeding date + 340 days
Birth is called	Foaling
Mother	Mare
Young	Foal

The foaling date is an estimate, and the 320 to 370 day display is a planning window, not a normal-range boundary. eXtension calls foals born before day 326 premature and usually in need of immediate veterinary attention; Colorado State calls births before day 320 premature and gestation beyond day 360 prolonged.

Signs foaling is near

Some signs are less obvious in mares carrying their first foal.

Udder development
Abdomen drops
Wax appears on teat ends
Vulva relaxes
Vulva lengthens
Mare isolates herself
Mare goes off feed
Restlessness
Frequent lying down and standing
Pawing
Looking at the flanks

Horse pregnancy timeline

Days 14 to 18	A veterinary ultrasound can check pregnancy and twins.
About day 25	The embryo heartbeat should be visible on ultrasound.
Days 56 to 120	Fetal sex may be assessed by ultrasound.
Last 2 to 3 weeks	The abdomen may drop as muscles relax.

Frequently asked questions

How long is a horse pregnant?

The horse calculator uses an average of 340 days after breeding, about 11 months, while an individual mare may foal earlier or later.

How do I calculate a mare foaling date?

Enter the breeding date and the horse calculator adds 340 days for an estimated foaling date and shows its Foaling Planning Window.

What signs show that a mare is near foaling?

A mare may show udder development, teat waxing, a relaxed vulva, restlessness, repeated lying down and pawing near foaling.

When should I call a veterinarian during foaling?

Merck general equine guidance says that after the water breaks, call your veterinarian if there is no significant progress within 10 to 15 minutes, and immediately if the foal is not delivered within 30 minutes. If the membrane that first appears at the vulva is bright red and velvety instead of pale and white, the placenta has separated early; Merck says it must be broken open immediately and the foal delivered, or the foal will not get enough oxygen. Call your veterinarian immediately.