Last updated: April 13, 2026

Mare Gestation Calculator — Horse Gestation

Based on 3 sources
100 people find this calculator helpful

Table of contents

Horse gestation period 🐎

The gestation period for a horse typically ranges from 320 to 362 days, with an average of approximately 340 days. This can vary depending on breed, age, health, and litter size.

How to calculate the due date

Simply enter the breeding or mating date and this calculator will add the average gestation period to provide an estimated due date, along with the earliest and latest expected dates.

Stages of pregnancy

Early Embryonic (Days 140)

Embryo travels through the uterus and implants. The embryo is very fragile during this period.

Organogenesis (Days 41120)

Major organ systems develop. The embryo becomes a fetus around day 40.

Fetal Growth (Days 121270)

Rapid growth. Most of the foal's size is gained during this period.

Pre-Foaling (Days 271340)

Foal reaches full development. Mare's udder begins to fill ('bagging up').

Fun facts 🐎

  • Horse gestation averages 340 days but can range from 320 to 362 days.
  • Colts (males) tend to be carried slightly longer than fillies (females).
  • Most mares foal at night in the wild for predator protection.

Did we solve your problem today?