Horse Gestation Calculator

By the DueBarn team. Updated November 10, 2026.

Enter the breeding date to get the expected foaling date, the normal range, and how far along your mare is today.

—
Expected foaling date
—
Earliest normal
—
Latest normal
—
Today

How long is a horse pregnant?

Mares average about 340 days (11 months), but anything from about 320 to 370 days is considered normal. Mares bred early in the year often carry longer than mares bred in summer, and individual mares tend to repeat their own pattern.

Foaling date = breeding date + 340 days

BredDue, day 340Normal window: 320 to 370 daysUltrasoundBoosters
Typical mare pregnancy from breeding to foaling. The shaded part is the normal 320 to 370 day foaling window.

Pregnancy milestones

DayWhat happens
14 to 16Ultrasound to confirm pregnancy and rule out twins
25 to 30Heartbeat visible on ultrasound
Months 5, 7 and 9Equine herpesvirus (EHV-1) vaccines, per your vet
About 300Pre-foaling boosters
320 to 370Normal foaling window
Signs of foaling. Udder fills over the last 2 to 4 weeks, wax appears on the teats 1 to 4 days before, and milk calcium rises sharply. Most mares foal at night.

Frequently asked questions

How many months is a horse pregnant?

About 11 months, or 340 days on average.

Can a mare be overdue?

Gestations up to 370 days and longer can be normal if the mare is healthy. Ask your vet to check her if she passes 360 days.

When should a mare be checked after breeding?

At 14 to 16 days by ultrasound, which is the best time to detect and manage twins.

Reference charts

Embed this calculator on your website

Free for blogs, suppliers, clubs and schools. Paste this code into your page. It stays up to date automatically, and the short credit line under it must stay in place.

More gestation calculators

Cow Gestation Calculator

Calving date by breed, with the normal window.

Goat Gestation Calculator

Kidding date for dairy, meat and pygmy goats.

Sheep Gestation Calculator

Lambing date for ewes, with the normal window.

Dog Pregnancy Calculator

Whelping date with week-by-week milestones.

Cat Pregnancy Calculator

Kitten due date and stages of cat pregnancy.

Rabbit Gestation Calculator

Kindling date and nest box date.

Last updated November 10, 2026. Results are estimates for planning. See how we build and check our tools in our editorial policy. Found an error? Tell us.