Mare gestation calculator.
Find out when your mare is due. Enter the breeding date and the calculator estimates the due date from the average mare gestation, with the earliest and latest dates too.
Breeding date
LiveMare gestation lasts about 320 to 370 days, averaging near 340. The due date is the breeding date plus the average gestation; the range gives the earliest and latest.
Estimated foaling date
May 7, 2027
based on average gestation
An estimate based on average mare gestation; individual animals vary. Not veterinary advice. Calculations run in your browser; nothing you enter is stored.
How it works
Counting from breeding
Mare gestation lasts about 320 to 370 days from breeding, about eleven months, with an average near 340 days. The calculator adds the average to the breeding date to estimate the due date, and the 320 to 370 day range gives the earliest and latest you should expect a foal.
Colts are often carried a little longer than fillies, and normal gestation varies widely between mares. Treat the due date as a window of a few days rather than a single fixed day.
Reference
Gestation by animal.
Typical pregnancy lengths for mares and other common animals, for comparison.
| Animal | Gestation |
|---|---|
| Cat | 63 to 67 days |
| Dog | 58 to 68 days |
| Cow | 279 to 287 days |
| Goat | 145 to 155 days |
| Sheep | 144 to 152 days |
| Horse | 320 to 370 days |
The full guide
The complete guide to mare gestation.
How long mares carry, the stages to expect, and when to get help.
How long are mares pregnant?
Mare gestation runs about 320 to 370 days from breeding, averaging around 340, or about eleven months. Counting from the breeding date gives the most reliable estimate of when a foal are due.
Colts are often carried a little longer than fillies, and normal gestation varies widely between mares.
Stages of pregnancy
There are few outward signs for months. The belly rounds out through the last trimester, and in the final weeks the udder fills and the teats may wax, with droplets of colostrum appearing days before foaling.
A vet can confirm pregnancy by ultrasound from about two weeks and monitor the mare through the long gestation.
Preparing for the birth
Move the mare to a clean, large foaling stall or a safe paddock a few weeks before the due date and keep her vaccinations current. Mares often foal at night and very quickly, so quiet observation is key.
Waxing of the teats and relaxation around the tailhead are signs foaling is near.
When to call the vet
Call a vet urgently if the mare passes about 370 days, or if the waters break and no foal appears within 20 to 30 minutes, since equine labour is fast and any delay is an emergency. This tool is for planning only and does not replace veterinary care.
The formula
Date plus
gestation.
The due date is the breeding date plus about 340 days, with a foal normally arriving between 320 and 370 days.
Cow gestation ›# Mare due date
due = breeding_date + gestation
mare gestation = 320 to 370 days
# average 340 days
breeding + 340 daysQuestions
Mare gestation questions.
How long is a mare pregnant?
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About 320 to 370 days from breeding, averaging around 340 days, about eleven months. The calculator uses this to estimate the due date.
How do I calculate a mare due date?
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Add about 340 days to the breeding date. Enter that date above and the calculator gives the estimated due date plus the earliest and latest.
Can the due date be a few days off?
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Yes. Colts are often carried a little longer than fillies, and normal gestation varies widely between mares. Treat the result as a window from 320 to 370 days.
When should I contact a vet?
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Contact a vet if the pregnancy runs well past 370 days, if labour stalls without progress, or if the animal seems distressed. A prenatal check-up is always worthwhile.
Is this mare gestation calculator free?
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Yes. It is completely free with no sign-up, and every calculation runs locally in your browser, so nothing you enter is stored or sent anywhere.
About the developer
Jean Borg
Jean builds and maintains every calculator on freecalculators.pro from Malta, with a focus on tools that are fast, free and show their working. The mare gestation calculator estimates a due date from average mare gestation and is for planning, not veterinary advice.