Horse Gestation Calculator
Enter the breeding date and get the mare's expected foaling window, the normal 320–370 day range, the premature cutoff and the 11-month date, from university extension figures.
If the mare was covered more than once, enter the first and last dates. The result updates as you type.
Expected foaling
Tue, March 16, 2027 – Sun, March 21, 2027
Average gestation 335–340 days · normal range Mon, March 1, 2027 – Tue, April 20, 2027
| Average window (335–340 days) | Tue, March 16, 2027 – Sun, March 21, 2027 |
| Normal range (320–370 days) | Mon, March 1, 2027 – Tue, April 20, 2027 |
| Premature if born before (326 days) | Sun, March 7, 2027 |
| 11 months after the last breeding (common breeder rule) | Mon, March 15, 2027 |
What this page cannot tell you
Whether the mare is pregnant, or when she will actually foal — individual mares vary, and day length, season, foal sex and nutrition all shift it. Only an ultrasound or a veterinary exam confirms pregnancy; watch for foaling signs and talk to your vet as the date nears, especially past 365 days.
How to calculate a mare's foaling date
- Enter the breeding date. The cover, insemination or ovulation date.
- Add the last date if bred more than once. The window then runs from the first to the last date.
- Read the foaling window. Average 335–340 days, normal range 320–370 days.
- Note the key dates. The premature cutoff (326 days) and the 11-month date.
10 situations where a horse gestation calculator helps
Planning foaling watch
Know when to start checking the mare at night.
Moving to a foaling stall
Get the mare settled before the window opens.
Booking the vet
Schedule pre-foaling checks and vaccinations.
Spotting a premature foal
Foals born before 326 days are considered premature.
Long pregnancies
See when a mare has gone past the normal range.
Planning next season's breeding
Expected foaling dates shape rebreeding plans.
Selling an in-foal mare
Give buyers a due window.
Multiple covers
Enter first and last dates for an accurate spread.
Comparing with the 11-month rule
See how the breeder's rule of thumb sits inside the window.
Days in foal
The page shows how many days have passed since breeding.
Where the numbers come from
The figures are from University of Nebraska–Lincoln Extension NebGuide G1874, 'The Foaling Mare' (Kathleen P. Anderson, Extension Horse Specialist, 2008): 'The average gestation length (duration of pregnancy) of mares is 335 to 340 days, but can range from 320 to 370 days.' Foals are considered premature if delivered at less than 326 days, and many breeders calculate the expected foaling date at 11 months after the last breeding — though most mares carry longer than that. The Merck Veterinary Manual's table of approximate gestation periods lists the horse at 11 months.
The page adds those day counts to your breeding date. With first and last covers, the early edge of each window counts from the first date and the late edge from the last. The 11-month date is the same calendar day eleven months after the last breeding (moved to the month's end where needed).
Limits: individual mares vary, and the NebGuide notes that factors such as season and day length, foal sex and nutrition affect gestation length. Only an ultrasound or veterinary exam confirms a pregnancy. Everything runs in your browser.
Sources
- University of Nebraska–Lincoln Extension — G1874 The Foaling Mare — 335–340 day average, 320–370 range, premature < 326 days
- Merck Veterinary Manual — Approximate Gestation Periods — Horse: 11 months
Frequently asked questions
How long is a horse pregnant?
University of Nebraska Extension gives an average of 335 to 340 days, with a normal range of 320 to 370 days.
When is a foal premature?
When born at less than 326 days of gestation, per UNL Extension; such foals usually need immediate veterinary attention.
What is the 11-month rule?
Many breeders estimate foaling at 11 months after the last breeding; most mares go a little longer.
My mare was bred twice — which date do I use?
Enter both; the window spans from the first to the last date.
My mare is past 370 days — is that normal?
It's beyond the normal range in the NebGuide; talk to your veterinarian.
Can this confirm pregnancy?
No — only an ultrasound or veterinary exam can.
Related tools
Cow Gestation Calculator
Enter a breeding or AI date and get the calving date at the traditional 283 days and at the shorter average a 101,787-mating Angus study found — with the window most calves arrive in.
K-State Extension Beef Tips (July 2026), gestation length in modern beef cattle
Sheep Gestation Calculator
Enter a breeding date — or the dates a ram or crayon colour was on — and get the lambing window from the Merck Veterinary Manual's 144–150-day normal gestation.
Merck Veterinary Manual (normal sheep gestation 144–150 days)
Goat Gestation Calculator
Enter a breeding date — or the dates a buck ran with the does — and get the kidding window from the Merck Veterinary Manual's 145–155-day goat gestation.
Merck Veterinary Manual (goat gestation 145–155 days, average 150)
Pig Gestation Calculator
Enter a breeding date and get the farrowing date at 114 days and the 113–116-day farrowing window, plus a gestation chart of key dates.
Merck Veterinary Manual (pig 114 days); Pork Industry Handbook (113–116 days)
Honey Yield Calculator
Weigh your supers before and after extraction and get the honey harvested in pounds, kilograms, gallons and full jars, with yield per hive against USDA's U.S. average.
National Honey Board (12 lb per gallon); USDA NASS Honey, March 2026
Honey Production Calculator
Enter your colonies and state to estimate honey production in pounds and its value, from USDA's 2025 yield per colony and honey prices — or your own figures.
USDA NASS Honey (March 2026): 2025 yield and price by state