Horse Pregnancy Calculator

Last Breeding / Service Date:

Gestation Estimates

Earliest Safe Arrival (320 days):

Expected Foaling Date (340 days):

Late Delivery Range (370 days):

*Note: Average horse gestation is 340 days, but ranges from 320 to 370 days are considered normal.*

How to Use the Horse Pregnancy Calculator

Calculating your mare's due date is the first step in preparing for a successful foaling season. To use this calculator, simply input the "Service Date" or the last date the mare was bred. The calculator uses the industry-standard average of 340 days to provide an expected foaling date, while also highlighting the window of safety between 320 and 370 days.

Understanding the Horse Gestation Period

A horse's pregnancy is significantly longer than a human's, typically lasting about 11 months. However, equine gestation is notoriously variable. While the 340-day mark is the gold standard for breeders, many factors can influence when a foal actually arrives:

Time of Year: Mares bred early in the spring (February/March) tend to have slightly longer gestations than those bred later in the summer.
Gender of the Foal: Statistically, colts (males) are often carried 2 to 7 days longer than fillies (females).
Breed Differences: Thoroughbreds and Quarter Horses typically stick close to the 340-day average, while some pony breeds may foal slightly earlier.
Individual Mare History: Many mares are "consistent" in their own timing. If a mare foaled at 350 days previously, she is likely to do so again.

Preparation Timeline for Foaling

Using the date provided by the horse pregnancy calculator, you should plan the following milestones:

Month 10 (300 Days): Move the mare to the location where she will foal. Boost vaccinations (especially EWT and West Nile) to ensure colostrum quality.
2-4 Weeks Before Due Date: Observe the mare for "bagging up" (udder development) and "waxing" (beads of colostrum on teats).
The Foaling Window: Start night checks or set up foal monitors once you hit the 320-day mark.

Example Calculation

If your mare was successfully bred on May 1st:

Earliest Date (320 days): March 17th of the following year.
Expected Date (340 days): April 6th of the following year.
Late Date (370 days): May 6th of the following year.

Always consult with an equine veterinarian throughout the pregnancy to ensure the health of both the mare and the developing foal.