How Long Are Horses Pregnant? Mare Gestation Chart and Foaling Date Calculator

Horses are pregnant for about 340 days, a little over 11 months, but a normal pregnancy can run anywhere from about 320 to 370 days. University of Nebraska extension puts the average mare gestation at 335 to 340 days with a range of 320 to 370, so the honest answer for your mare is a foaling window, not a single date. Enter her breeding date in the free Creatures horse gestation calculator and it returns the 340-day estimate and that whole window in a few seconds, no account needed.

The width of that window is normal, and most of it is explained by things you can see coming: the time of year she foals, whether she carries a colt or a filly, and above all her own history. This guide gives you a breeding date to foaling date chart you can read at a glance, explains how to count from the right date, covers ponies and miniature horses, walks through the pregnancy month by month, and shows how to keep the whole timeline on your mare’s free Creatures profile instead of a barn whiteboard. The Creatures horse page gathers the breeds and care guides that go with it.

How long is a horse pregnant?

Every primary source lands in the same place. The University of Nebraska extension publication on management of the pregnant mare gives an average of 335 to 340 days and a range of 320 to 370. The University of Georgia’s bulletin on understanding gestation in the mare puts the average at about 338 days within the same 320 to 370 range. The University of Minnesota’s guide to caring for your mare during breeding and foaling says usually 335 to 342 days, and notes that pregnancies occasionally run from 315 to more than 400 days. So 340 days is a sensible planning midpoint, and 11 months is a fair shorthand, as long as you remember it is a midpoint.

Two numbers at the edges matter more than the average:

• The early edge. The Merck Veterinary Manual defines prematurity in foals as birth before 320 days. Nebraska extension uses 326 days and says those foals usually need immediate veterinary attention. A foal arriving before that point, or any foal that is weak, small or slow to stand, needs your veterinarian now.
• The late edge. A mare at 350 or even 360 days is often perfectly normal, especially a mare who has carried long before. Merck’s neonatal chapter notes that normal gestation ranges from 310 days to more than 370. What turns “late” into a problem is not the count alone but the count plus anything unusual about the mare, which is why a mare well past her own usual length deserves a call to your veterinarian rather than more waiting.

Many mares repeat themselves. Nebraska extension notes that mares vary a lot from one another, but many individual mares follow a similar pattern year after year. If your mare carried her last foal to 352 days, plan around 352 this time and use the textbook range as the outer frame. That is the single best reason to write down every breeding date and every foaling date.

Horse gestation chart: breeding date to foaling date

The chart below adds 340 days to each breeding date and shows the 320 to 370 day normal range beside it. It is an estimate for planning, not a prediction for your mare. Where the span crosses February 29 in a leap year, each date lands one day earlier.

Foaling dates fall in the calendar year after the breeding for everything bred from about late January on, so a mare bred on April 15 is due around March 21 of the next year. For a date that is not on the chart, the horse gestation calculator does the arithmetic for any day; for a pony or a jenny, use the pony gestation calculator or the donkey gestation calculator. The full set of Creatures gestation calculators covers 19 species.

How to calculate a mare’s due date

The math is simple: breeding date plus 340 days is the estimated due date, and the window to be ready for runs from about day 320 to day 370. The part that takes judgment is which date to start from.

• Your veterinarian tracked ovulation by ultrasound. Count from the ovulation date. It is the closest thing you have to the day of conception, and it gives the tightest estimate.
• She was hand-bred or inseminated more than once in one heat. Use the last breeding date for a working estimate, and keep the earlier dates on record in case she foals early.
• She was pasture-bred with a stallion over several days or weeks. Use the first and last day of exposure. The calculator’s Exposure Window mode takes both dates and widens the foaling window to match, which is more honest than picking one day and hoping.
• Your records are incomplete. Widen the window rather than narrowing it, and ask your veterinarian to estimate the stage of pregnancy on an exam. A calculator cannot rescue a missing breeding date.

The horse gestation calculator offers both Exact Breeding Date and Exposure Window modes, returns the 340-day estimate with the 320 to 370 day planning window, and lists the pregnancy milestones and signs that foaling is near. It is free and saves nothing, so copy the result somewhere you will see it again. The help center has a short walkthrough on using the gestation calculator.

What makes a mare carry longer or shorter

Season and day length. This is the biggest predictable factor. Nebraska extension notes that mares foaling in late spring and summer, when days are long, tend to have shorter gestations than mares foaling in January or February. Breeders who want early foals sometimes put bred mares under lights: the same publication reports that artificially lengthened days in the last third of pregnancy have been shown to shorten gestation by about 10 days. A lighting program is something to plan with your veterinarian, not to improvise.

The sex of the foal. Colts tend to be carried 2 to 7 days longer than fillies, according to Nebraska extension. You usually will not know which you are expecting, so this is one more reason to plan for the window.

The individual mare. Some mares are consistently long and some consistently short. Her own record beats any chart.

Nutrition and body condition. A mare’s plane of nutrition has some influence on gestation length, per the same extension source. Keep a broodmare in steady, moderate condition; the Henneke body condition scoring guide explains the 1 to 9 scale your veterinarian will use.

Endophyte-infected tall fescue. Pregnant mares grazing fescue infected with the toxic endophyte can carry two weeks or more past normal, with a thickened placenta, little or no milk, and difficult births, according to University of Georgia extension on fescue toxicosis in horses. The same publication says veterinarians recommend moving mares off infected fescue pasture 45 to 90 days before the expected foaling date. If you are in fescue country, ask your veterinarian and your extension office about your pastures well before the last trimester.

Breed. Breed matters less than people expect. Research comparing European horse breeds has found that breed explains some of the variation in gestation length but that body size does not predict it. A heavy draft mare like a Percheron and a light riding mare both plan around the same 320 to 370 day window.

Pony and miniature horse gestation

Ponies and miniature horses are horses, and they follow the same general pattern: roughly 11 months, with the same wide normal window. The small published studies we could find put pony averages right around the horse figure:

• Six Shetland mares in a 2020 study of foaling in horses of different size averaged 329.5 days, with births from day 312 to day 338.
• Seven pregnancies in Hokkaido native ponies and pony crosses, in a 2021 fetal growth study, averaged 341 days, ranging from 332 to 359.

That is the honest picture: ponies and minis are not reliably shorter or longer than full-size mares, and published data specific to the American Miniature Horse is thin. Plan around 330 to 340 days and the full window, and lean on your own mare’s history as soon as she has one. The pony gestation calculator uses a 330-day midpoint with a 320 to 360 day window and says plainly that its average rests on a small Shetland study.

What does change with small equines is foaling risk. A 2025 study of 78 difficult births in miniature horses and donkeys seen by one veterinary practice found abnormal limb and neck positions were the most common causes, and that the longer a difficult birth took to resolve, the worse the outcome. Only 13 of the 78 foals in that study survived, while nearly all the mares did. If you breed minis, agree on a foaling plan with your veterinarian before the window opens, including who comes out at night and how fast. The Miniature Horse, Shetland Pony and Welsh Pony pages cover the breeds themselves.

Donkeys, mini donkeys and mules are a different calculation. Use the donkey gestation calculator for a jenny rather than the horse chart above.

Use the mare foaling preparation timeline for a worked example and veterinary milestones after calculating the broad birth window.

Mare pregnancy timeline, month by month

Most of what happens in a horse pregnancy is invisible, and most of the owner’s jobs are on a schedule. The timeline below pulls the key dates together; your veterinarian sets the actual plan for your mare.

Months 1 to 2: confirm, and check for twins

You do not have to wait months to know. Colorado State University’s Equine Reproduction Laboratory recommends a first ultrasound 14 to 16 days after ovulation, because an exam on or before day 16 is also the best chance to find and manage twins. Twin pregnancies are dangerous in mares and are associated with late-term abortion, per the Georgia bulletin, so vets look for a second embryo early, while there is still a safe way to deal with it. A heartbeat is usually visible around day 25, and CSU suggests a further exam around day 35. The Merck Veterinary Manual’s page on pregnancy determination in horses describes the same early schedule: days 14 to 18 for pregnancy and twins, then days 25 to 30 to check normal development and recheck for twins. Record each scan on the mare’s profile as it happens.

Months 3 to 7: steady routine, and the EHV series

For the middle of pregnancy, a mare’s needs stay close to maintenance, and the goal is a quiet, consistent routine with good forage and clean water. The one pregnancy-specific vaccine schedule is the equine herpesvirus (EHV-1, rhinopneumonitis) abortion series. Merck’s guidance on vaccination in breeding horses lists EHV-1 at 5, 7 and 9 months of gestation, and the AAEP vaccination guidelines are the reference most equine vets work from. Which products and exactly when are your veterinarian’s call, not this article’s. The horse vaccination guide covers core versus risk-based vaccines across a horse’s life.

Months 8 to 11: the foal grows, and she needs more

Most of the growth comes late. The University of Minnesota guide says a mare gains 9 to 12 percent of her body weight during pregnancy, two-thirds of it in the last three months, and that her protein requirement rises from about 8 percent of the diet early on to 11 to 12 percent late in pregnancy, with calcium and phosphorus needs rising too. At the same time the foal takes up room, so some mares eat less hay just when they need more nutrition. That is why late-pregnant mares are often moved onto a balanced broodmare ration alongside good forage rather than simply given more hay. The exact ration depends on her condition, your forage and her age, so set it with your veterinarian or an equine nutritionist. The horse feeding guide and horse hay guide cover the basics this builds on.

About four to six weeks before her due date, Merck says vaccines that need annual boosters should be given, so her colostrum is loaded with antibodies when the foal nurses. Merck adds that the foal must drink that colostrum within its first 24 hours of life for the antibodies to be absorbed.

Getting ready for foaling

Preparation starts before the window opens, not on the night. Move her to the place she will foal a few weeks ahead so the move does not stress her. A foaling stall should be large, clean and deeply bedded with clean straw, with smooth walls, fresh water and hay; a small paddock with safe fencing works too in good weather. Test any camera or alarm before you need it, post your veterinarian’s number and a backup where everyone on the farm can find it, and put your foaling kit in one visible place. If you do not yet have an equine vet who will come out at night, fix that now; our guide on how to find an equine vet covers what to ask.

Watch the mare more than the calendar. Nebraska extension’s guide to the foaling mare gives the usual order:

• Udder development begins 2 to 6 weeks before foaling.
• Relaxation of the muscles around the tailhead and pelvis shows in the last 7 to 14 days.
• Milk moves into the teats about 4 to 6 days before foaling.
• Waxing, small beads of colostrum on the teat ends, appears 1 to 2 days before foaling. Some mares never wax, and some drip milk for days.

Once labor starts, horse births are fast. The same publication says the delivery stage is usually over in 10 to 30 minutes, and Minnesota’s guide says to call your veterinarian if the white, fluid-filled amnion or a foot has not appeared within about 10 minutes of the water breaking, or if progress stops for more than 10 minutes. Anything that looks wrong is an emergency, and the right move is to call, not to wait or pull. Our foaling guide covers the stages of labor, normal presentation, the foaling kit and the first hours with the foal in detail; read it before your mare’s window opens.

After the birth, write down the date, the time, when the foal stood and nursed, and when the placenta passed. Next year, that date is the most accurate gestation figure you will have for this mare.

Tracking a mare’s pregnancy on Creatures

A horse pregnancy has more dates in it than most people can hold in their head for 11 months: the covers, the ovulation, the 14-day scan, the heartbeat check, three EHV doses, the pre-foaling boosters, the fescue move, the window, and the foaling. Creatures keeps them together on the mare’s profile.

Without an account. The horse gestation calculator and the pony gestation calculator are free for anyone and give you the estimate, the window and the milestones. When the foal is on the way, the free horse pedigree chart maker builds a printable three-generation pedigree from the sire and dam, also with no account.

With a free account, record the breeding. Add your mare, then add a Breeding & Reproduction record and turn on Track as breeding cycle. Enter the service method, the stallion (a Creatures profile or just a name for an outside stallion) and the Service start date, plus a Service end date if she was pasture-bred over several days, which widens the window to match. If your veterinarian gives you an expected date from an ultrasound, use Projected date override rather than changing the breeding date. Step by step: recording a breeding.

Follow the pregnancy. The mare’s Breeding tab shows the expected date and window, milestones and a progress bar, and treats it as a planning guide, not a guarantee. When a scan gives better timing, Adjust projection moves the expected date, the window, the milestones and the open reminders together. You can add dated progress photos along the way. See tracking pregnancy and progress.

See every expecting mare in one place. The Breeding dashboard lists active cycles by due date, grouped into Expecting, Due soon and Overdue. Overdue only means the window has passed without a recorded foaling; it is a prompt to check on her and call your veterinarian, not a health assessment. More in the breeding dashboard. Set your own reminders for the EHV doses and pre-foaling boosters, since missing the 7-month or 9-month dose is easy in a busy barn; see reminders and upcoming care.

Record the foaling. From the Breeding tab, record the birth with the count born alive, and Creatures closes the cycle and lets you create the foal’s own profile, already linked to its dam. That is where the foal’s vaccinations, deworming and farrier records begin; our horse health records guide covers what to keep. See recording births and creating a litter. Stuck on a name? Try the foal name generator.

If you are still planning the cross, our guide to horse stud fees explains what a breeding contract and live foal guarantee usually cover.

Frequently asked questions

How many months is a horse pregnant?

About 11 months. The average is around 340 days, which is 11 months and roughly a week, and a normal pregnancy runs from about 320 to 370 days, or roughly 10.5 to just over 12 months.

Can a horse be pregnant for 12 months?

Yes. A pregnancy of 365 days or a little more is within the normal range that extension sources give, especially for a mare foaling in late winter or early spring or one with a history of long pregnancies. Merck notes normal gestation can run past 370 days. Keep your veterinarian informed as she passes her own usual length, and call sooner if anything about her seems off.

What is the earliest a mare can safely foal?

Merck defines a foal born before 320 days as premature, and Nebraska extension uses 326 days. Foals born before about 326 days should be seen by your veterinarian promptly even if they stand and nurse, because prematurity is not always obvious. A foal born inside the normal window that stands, nurses and looks mature is usually fine.

How long are miniature horses pregnant?

About the same as full-size horses: roughly 11 months, around 330 to 340 days, within the same wide normal window. Published studies of small ponies average about 330 to 341 days. Minis can have difficult births, so plan the foaling with your veterinarian in advance.

How soon can you tell if a mare is pregnant?

A veterinarian can confirm pregnancy by ultrasound from about 14 to 16 days after ovulation, and that early scan also checks for twins. Outward signs such as a bigger belly show only months later, and a mare can look round without being in foal.

How accurate is a horse gestation calculator?

As accurate as the date you give it, and no more precise than the biology. Any calculator can only add the average to your breeding date and show the normal range. Counting from a vet-confirmed ovulation date, and adjusting for your mare’s own history, gets you closer than any chart.

Do this next on Creatures

Whether you are counting down to this year’s foal, planning next season’s breeding, or looking for a mare or a foal of your own, these are the useful next steps.