How Long Are Horses Pregnant? Mare Due Dates and Care

The short answer to “how long are horses pregnant” is about 340 days—roughly 11 months—but normal gestation commonly ranges from about 320 to 370 days. Treat the calculated due date as a planning estimate, not an appointment. An individual mare may foal earlier or later.

A foal born before 320 days is generally considered premature. Survival depends on the foal’s maturity and the veterinary care available; foals born before 300 days rarely survive. Call an equine veterinarian immediately if premature labor or birth appears possible.

How Long Are Horses Pregnant in Days and Months?

The average horse gestation period is about 340 days, or approximately 11 months. The commonly cited range is about 320–370 days, although recorded gestations have ranged from 315 to 387 days. Those wider figures reflect variation; they don’t guarantee that every foal born within them will be healthy or mature.

The mare gestation period varies enough that a calendar date can’t predict exactly when a foal will arrive. Use the average to plan and the broader window to decide when to prepare and monitor. A mare that hasn’t foaled on day 340 isn’t automatically overdue or in trouble.

A foal arriving before day 320 is generally classified as premature. Birth before day 300 is especially concerning because survival is rare. Involve a veterinarian rather than trying to manage delivery yourself.

How to Calculate a Mare’s Due Date and Foaling Window

For a simple estimate, count the breeding or ovulation date as day zero and add 340 days. Mark earlier and later planning dates, too. The date of covering may not be the date of ovulation, especially if a mare was bred more than once, so the result is a window rather than a guaranteed due date.

Worked example: mare bred March 15

Assume a non-leap-year calendar and a mare covered on March 15. Count March 15 as day zero:

• Day 320: January 29 of the following year. Use this as an early monitoring landmark, not a prediction that foaling will happen then.
• Day 340: February 18. This is the estimated date based on the average gestation length.
• Day 360: March 10. Continue monitoring and contact your veterinarian as this later landmark approaches.
• Day 370: March 20. If the mare hasn’t foaled, arrange a veterinary assessment.

These are calendar calculations, not clinical cutoffs. The normal range is broad, and the average can’t predict an individual mare’s delivery date.

If a stallion covered the mare on multiple dates, calculate a possible window from each date. Keep your horse breeding records and ask your veterinarian whether the timing of ovulation can be estimated more closely. A calendar can’t establish the exact conception date or tell you whether the foal is ready to be born.

Put the estimated date, monitoring landmarks, veterinary check-ins, and emergency contact information on one calendar. Foaling signs and the mare’s condition take priority over the estimated date.

Pregnancy Checks and the Horse Gestation Timeline

Early observations may suggest pregnancy, but they can’t confirm it. A mare that doesn’t return to estrus, or whose behavior seems different, may still not be pregnant. Changes in appetite, temperament, or appearance aren’t reliable diagnostic tests either. Arrange a veterinary pregnancy check even when the signs seem convincing.

Early signs before pregnancy confirmation

After breeding, note whether the mare appears to return to her usual estrous cycle, but don’t treat that observation as proof either way. Lack of an obvious heat, a change in behavior, or a fuller abdomen can have other explanations. Keep breeding records and schedule an ultrasound pregnancy check with an equine veterinarian.

When to schedule ultrasound checks

An ultrasound around days 14–16 is commonly used to confirm pregnancy and check for twins. A follow-up around days 25–30 can assess viability; the veterinarian may recommend another scan around days 45–60, depending on the findings and the mare’s circumstances.

Twin pregnancies carry substantial risks. Early detection gives the veterinarian an opportunity to discuss management. Don’t try to interpret an ultrasound image or make decisions about a twin pregnancy without veterinary guidance.

The embryo is described as becoming a fetus after day 40 of gestation. The month-by-month table below is a planning aid, not a diagnostic chart. Development and recommended checks can vary, so confirm the timing of scans and care with your veterinarian.

Horse pregnancy timeline: month-by-month milestones

Month	Approximate days	Development or pregnancy checkpoint	Owner action
1	0–30	Early embryonic development; the early pregnancy scan can check for twins	Arrange the initial ultrasound around days 14–16 and a follow-up around days 25–30 as advised.
2	31–60	The embryo transitions to a fetus after day 40	Ask whether a further scan around days 45–60 is appropriate.
3	61–90	Pregnancy continues as fetal development progresses	Keep breeding and veterinary records together.
4	91–120	Ongoing growth	Monitor body condition and discuss any ration changes with your veterinarian.
5	121–150	Mid-gestation care planning becomes important	Review EHV-1 vaccination timing and risk with your veterinarian.
6	151–180	Pregnancy continues; individual care needs vary	Use veterinary advice and, where appropriate, fecal testing to guide parasite control.
7	181–210	Continue planned pregnancy monitoring	Review vaccination, body condition, and exercise with your veterinarian.
8	211–240	Later pregnancy; the mare’s nutritional needs may change	Assess the full ration and forage rather than adding supplements automatically.
9	241–270	Plan late-pregnancy checks and foaling arrangements	Discuss fescue exposure and the timing of any recommended boosters.
10	271–300	Prepare the foaling area and emergency plan	Ask the veterinarian about pre-foaling vaccination based on the mare’s history.
11	301–340+	Foaling may occur around the average date or later	Have the kit and contact plan ready; monitor the mare for changes.

Horse Gestation Period by Breed and Body Size

Breed and body size may influence average gestation length, but they can’t tell an owner exactly when an individual mare will foal. The evidence available here supports a general tendency for ponies and miniature horses to average about 330–335 days compared with standard breeds. It doesn’t establish dependable, comparable ranges for every breed or size group.

Breed or size group	Published gestation range and population	Source and limitations
Ponies and miniature horses	Average reported around 330–335 days	A reported group average, not a guaranteed range for an individual mare.
Standard or light horses	The broad equine average is about 340 days; the commonly cited overall range is about 320–370 days	These figures describe horses generally, not a precise breed-specific prediction.
Warmbloods	No reliable breed-specific range established by the evidence summarized here	Avoid treating commonly repeated breed figures as universal.
Draft breeds	No reliable breed-specific range established by the evidence summarized here	A larger body size alone does not establish an individual due date.

Season may also affect gestation. One reported tendency is for mares bred during shorter winter days to carry about 10 days longer than mares bred during longer summer days, but that’s not a fixed rule for an individual mare. Some studies also report small differences associated with foal sex or mare age and foaling history; the evidence here doesn’t support using those factors to calculate a particular due date. Individual variation is more useful for planning than a presumed breed or seasonal adjustment.

Trimester Care Schedule for a Pregnant Mare

Plan care with an equine veterinarian who knows the mare’s health, vaccination history, forage, workload, and local disease risks. Nutritional needs depend on body condition and the whole ration. Late pregnancy can require closer assessment, but abrupt feed changes or unnecessary supplements aren’t a substitute for that assessment.

Trimester	Nutrition and body condition	Vaccination	Parasite control	Exercise and other checks
First: early pregnancy	Review forage, ration, and body condition; avoid unnecessary changes	Review vaccination history and local risks with the veterinarian	Use veterinary advice and testing to select any pregnancy-appropriate product	Discuss the mare’s current workload and any health concerns; complete pregnancy checks on the recommended schedule.
Second: middle pregnancy	Reassess body condition and forage as pregnancy progresses	Ask the veterinarian whether EHV-1 vaccination is indicated and when; some protocols use boosters during pregnancy	Base treatment on the mare’s history, exposure, and veterinary guidance rather than a blanket schedule	A healthy mare may be able to continue suitable work, but adjust for her condition and veterinary advice.
Third: late pregnancy	Review the complete ration and make any needed changes gradually	Discuss EHV-1 and pre-foaling boosters, including tetanus, in light of vaccine history and product directions	Confirm the timing and choice of any treatment with the veterinarian	Review fescue exposure, prepare the foaling area, and reduce or modify work as appropriate.

EHV-1 vaccination is commonly discussed at months 5, 7, and 9 of pregnancy, while boosters such as tetanus may be planned before foaling. Exact timing depends on vaccine history, product instructions, and veterinary advice. Confirm the mare’s schedule with her veterinarian rather than applying a generic calendar.

Endophyte-infected fescue can prolong gestation and reduce milk production, so tell the veterinarian if the mare has had access to fescue pasture or hay. Don’t make abrupt feed changes or administer a dewormer, vaccine, or medication without confirming that the product and timing are appropriate for this mare.

A healthy riding or sport mare may be able to remain in appropriate work, but her workload should be individualized and reviewed as pregnancy advances. Stop or change work if she appears uncomfortable or unwell, and ask the veterinarian for advice if she has complications or a history that affects exercise.

Signs a Mare Is Close to Foaling

Foaling signs can develop over time, and some mares show few obvious clues. Udder filling, relaxation around the tailhead, changes around the vulva, restlessness, or waxing at the teats can indicate that foaling is approaching, but no single sign gives an exact time. Call the veterinarian if milk drips before birth: the mare may lose colostrum, the antibody-rich first milk the foal needs.

Physical and behavioral foaling signs

Watch for changes in combination rather than relying on a single sign. A mare may become restless, separate herself, lie down and rise repeatedly, or show increasing udder development. Waxing or milk at the teats can occur near foaling, but timing varies. Keep notes and follow any monitoring plan your veterinarian recommends.

Labor and delivery warning signs

Once the water breaks, the second stage of labor—the delivery of the foal—normally progresses quickly. It is reported to last about 15–20 minutes, with 30 minutes described as a maximum. If delivery isn’t progressing promptly, call the veterinarian rather than waiting.

Call the veterinarian immediately if you see any of the following:

• A red, velvety membrane at the vulva instead of the usual pale sac. This may indicate premature placental separation, often called a red-bag delivery.
• No prompt progress after the water breaks or hard labor begins.
• A presentation other than the expected two front feet followed by the nose, or any position that looks abnormal.
• Heavy bleeding, severe distress, or a mare that appears suddenly ill.
• Milk dripping well before birth, especially if the mare is losing the colostrum the foal will need.

Don’t pull on the foal or membrane, and don’t delay a call while searching for equipment or trying to correct a presentation yourself. Follow the veterinarian’s instructions while help is on the way.

What to Do When a Mare Goes Past Her Due Date

Passing the estimated date doesn’t by itself mean something is wrong: 340 days is an average, and gestations commonly extend beyond it. Still, a mare who goes well beyond her estimate needs a plan based on verified breeding dates, her condition, and veterinary assessment—not guesswork or an attempt to induce labor at home.

Day 340 to day 360

• Day 340: Check the breeding and ovulation records and confirm which date you used for the calculation. If there were multiple coverings, the mare may be at a different gestational age than the calendar suggests. Increase observation and record changes in udder development, behavior, appetite, and any discharge.
• Around day 350: Continue logging observations. If your veterinarian has recommended milk testing, follow their instructions about when and how to use it; don’t treat a test result as a substitute for veterinary advice.
• As day 360 approaches: Call your veterinarian to review the dates and the mare’s condition. The veterinarian can decide whether an examination or additional monitoring is appropriate. Never induce labor without veterinary direction.

Day 365, day 370, and urgent exceptions

If the mare reaches days 365–370 without foaling, arrange a veterinary assessment even if she seems comfortable. Share all possible breeding dates and mention any fescue exposure, since endophyte-infected fescue can prolong gestation and reduce milk production. The veterinarian can determine whether further examination or monitoring is needed and what to do next.

Past day 370, follow the veterinarian’s monitoring or intervention plan. No single home remedy or date-based action is safe for every mare. Call immediately at any gestational age for colic, abnormal discharge, illness, signs of premature labor, or distress; don’t wait for the later-day checkpoints.

Foaling-Ready Checklist and Next Steps

Prepare the space, supplies, and communication plan before the mare shows active labor. Keep the veterinarian’s number somewhere visible and make sure anyone helping knows when to call. Ask the veterinarian to review the setup and any products intended for the foaling kit.

Basic foaling kit

• Several clean towels and disposable gloves.
• A clean bucket and mild soap for washing up.
• A tail wrap or bandage, a clock or timer, and a flashlight with working batteries.
• The veterinarian’s daytime and emergency numbers, plus a backup contact.
• A navel-care product only if the veterinarian recommends a specific product and use.

Set up a clean, well-lit foaling area with suitable bedding and remove hazards the mare or foal could encounter. Write the breeding dates, estimated day 340, monitoring window, and veterinary plan where helpers can see them. Arrange experienced backup and a transport plan in advance.

When to call the veterinarian

Call immediately for the labor warning signs above, including a red membrane, abnormal presentation, heavy bleeding, distress, or lack of prompt progress after the water breaks. Contact the veterinarian promptly if the mare loses milk before foaling or, after birth, if the mare or foal seems unwell or the foal isn’t progressing toward standing and nursing. Adequate colostrum matters to the newborn; don’t wait if nursing isn’t going well.

Retain the placenta for the veterinarian to inspect. It is generally expected to pass within 1–3 hours; if it hasn’t passed by then, call promptly and don’t pull on it. Ask your veterinarian what newborn checks and follow-up are recommended for the mare and foal, and keep the emergency contact plan in place through the first hours after delivery.

Key data

Month	Approximate Days	Development Checkpoint	Nutrition & Care Recommendations	Vaccination & Health Actions
1	0–30	Early embryonic development; the early pregnancy scan can check for twins	Review forage, ration, body condition, and workload. Arrange the initial ultrasound around days 14–16 and a follow-up around days 25–30 as advised.	Review vaccination history, local risks, and parasite control with the veterinarian; use veterinary advice and testing to select any pregnancy-appropriate product for parasite control.
2	31–60	The embryo transitions to a fetus after day 40	Ask whether a further scan around days 45–60 is appropriate.	Complete pregnancy checks on recommended schedule.
3	61–90	Pregnancy continues as fetal development progresses	Keep breeding and veterinary records together.	Not in source
4	91–120	Ongoing growth	Monitor body condition and discuss any ration changes with your veterinarian.	Not in source
5	121–150	Mid-gestation care planning becomes important	Reassess body condition and forage as pregnancy progresses.	Review EHV-1 vaccination timing and risk with your veterinarian (EHV-1 vaccination is commonly discussed at month 5).
6	151–180	Pregnancy continues; individual care needs vary	Use veterinary advice and, where appropriate, fecal testing to guide parasite control.	Use veterinary advice and, where appropriate, fecal testing to guide parasite control; base parasite control treatment on history, exposure, and veterinary guidance.
7	181–210	Continue planned pregnancy monitoring	Review body condition, exercise, and vaccination with your veterinarian.	Review vaccination and discuss EHV-1 vaccination timing with your veterinarian (EHV-1 vaccination is commonly discussed at month 7).
8	211–240	Later pregnancy; the mare's nutritional needs may change	Assess the full ration and forage rather than adding supplements automatically.	Not in source
9	241–270	Plan late-pregnancy checks and foaling arrangements	Discuss fescue exposure; review the complete ration and make any needed changes gradually.	Discuss fescue exposure, EHV-1, and the timing of any recommended boosters (EHV-1 vaccination is commonly discussed at month 9).
10	271–300	Prepare the foaling area and emergency plan	Review fescue exposure, prepare the foaling area, and reduce or modify work as appropriate.	Ask the veterinarian about pre-foaling vaccination (including EHV-1 and tetanus boosters) based on the mare's history.
11	301–340+	Foaling may occur around the average date or later	Have the kit and contact plan ready; monitor the mare for changes.	Pre-foaling boosters including tetanus may be planned before foaling based on history and product directions.

At a glance

FAQ

Can horses carry twins successfully?

Twin pregnancies carry substantial risks for the mare and foals, including pregnancy loss and premature birth. An early ultrasound can identify twins so an equine veterinarian can discuss management options.

Does the season affect when a mare foals?

Season can influence gestation length, with some studies reporting longer pregnancies in mares foaling earlier in the year. The effect varies, so season alone cannot predict an individual mare’s foaling date.

Do colts and fillies have different gestation lengths?

Some studies have found that colts are carried slightly longer on average than fillies. The difference is small compared with normal individual variation and is not reliable for predicting a due date.

Does a maiden mare carry her foal longer?

Age and whether a mare has foaled before may influence gestation length in some populations, but findings vary. A maiden mare’s due date should still be treated as an estimate, with monitoring tailored to her circumstances.