Horse Gestation Period: How Long Are Horses Pregnant (and What Changes the Due Date)
- Horse Education Online
- Dec 29, 2025
- 9 min read
The horse gestation period is usually about 11 months, but the real answer is a range, not a single number. Even healthy pregnancies can vary by several weeks, so a “due date” is best treated as a foaling window.
That variation happens because of season and day length, the individual mare’s history, and normal biological differences. Two mares bred on the same day can foal on very different dates and still be completely normal.
Educational only, and not a substitute for veterinary advice. Always confirm your mare’s plan and any concerns with your veterinarian.
If you want an estimated due date and timeline in seconds, use our Horse Gestation Calculator.
Quick answer
Average horse gestation period: about 340 days (roughly 11 months)
Common normal range: 320 to 370 days
Most useful planning window: expect foaling within about 2 to 4 weeks around your estimate, then adjust based on your mare’s history
If you don’t know the exact breeding date: use the first and last possible exposure dates to create a window, then plan your foal watch around that range instead of guessing one day
Pair the estimate with a health plan: Vaccines hub
What is the average horse gestation period?
The typical range (and why there isn’t one exact number)
A common, owner friendly range to remember is 320 to 370 days. Many mares land close to the middle, but it is normal to be earlier or later.
Some mares are also consistent year to year. You might notice the same mare tends to foal “early” or “late” compared to the calendar, even when everything is healthy. That pattern is one reason your veterinarian focuses on a window and the mare’s actual signs, not a single due date.
How accurate is a due date?
A due date is an estimate, not a guarantee.
The best way to use it is as a planning tool. It tells you when to start tightening routines, prepping the foaling area, and paying closer attention. Think “foaling window,” not “foaling day.”
If you want, tell me the breeding date (or the first and last possible dates), and I’ll help you phrase a tight “foal watch window” for the post and the calculator callout.
What makes a mare carry shorter or longer?
Breed and genetics
Some bloodlines and breeds tend to run a little shorter or longer on average. The important part for owners is this: breed can nudge the timeline, but it rarely overrides what your mare normally does.
If you have records from prior foals, use them. A mare that consistently foals around the same day count is often more predictive than breed stereotypes.
Season and day length
Season matters more than most people expect.
Mares bred early in the year (shorter daylight) can carry a bit longer, while mares bred later in the season often foal a bit sooner. The biology is basically the mare and foal timing birth closer to conditions that support a newborn.
This is one reason “my friend’s mare always goes 360 days” can be true for that barn, but not a rule for every mare everywhere.
Foal sex and mare history
There are general trends that get talked about, like colts sometimes carrying a touch longer, and older mares sometimes varying a bit more. Treat these as small influences, not something you can rely on for planning.
What matters more is the mare’s own history. If she has foaled before, her previous gestation lengths can help you set a realistic watch window.
Nutrition, body condition, and stress
Most timeline problems start when management swings to extremes.
Undernutrition, obesity, major routine disruptions, long hauling, and chronic stress can all affect pregnancy in different ways. The goal is boring consistency and appropriate condition, not aggressive feeding changes.
If you want a practical way to keep condition steady, start with the basics of forage first, then adjust concentrates only if needed. The simplest refresher is The Basics of Equine Nutrition: An Introductory Guide.
Health issues that can change the timeline
Most healthy pregnancies still vary. But there are situations where you should not wait it out.
If your mare looks unwell, has fever, colic signs, unusual discharge, sudden swelling, or anything that makes you say “this isn’t her normal,” call your veterinarian promptly. The right move here is not DIY. It is getting the mare assessed early, because pregnancy complications move faster than most owners expect.
Horse pregnancy timeline
First trimester (days 1–110)
This is the confirmation and “keep life steady” phase.
Most owners first think about pregnancy confirmation in this window. Your veterinarian will guide timing and method based on your breeding situation and the mare’s history.
Management wise, boring is good. Keep turnout and work routines steady, avoid major stress, and do not make dramatic feed changes unless your vet advises it.
Second trimester (days 111–220)
This is the quiet growth phase where many mares look normal, act normal, and can keep a consistent routine.
Owners sometimes overfeed here because the mare “looks pregnant.” In most cases, the better approach is to keep diet quality solid and condition appropriate, not to push calories early.
If you need a reference point for feeding math, it helps to know your mare’s approximate weight. Use How Much Does a Horse Weigh as a quick guide.
Third trimester (days 221–foaling)
This is when fetal growth accelerates and your planning becomes real.
Most owners start thinking about the foaling space, the observation plan, and what the last few weeks should look like. It is also the phase where you should tighten up your calendar, because you are no longer planning for “sometime in spring.” You are planning for a window.
If you are planning vaccine timing, start with what the common combo vaccines cover in 5 Way Equine Vaccine: What It Covers and Why It Matters.
Then map your dates with the 5 Way Vaccine Planner.
Horse pregnancy timeline table
Phase | Days (approx) | What’s happening (plain language) | Owner focus |
First trimester | 1–110 | Early development and pregnancy confirmation window | Keep routine steady, minimize stress, follow vet confirmation plan |
Second trimester | 111–220 | Quiet growth phase, mare often looks and acts normal | Maintain consistent condition, avoid overfeeding, keep normal turnout and work if appropriate |
Third trimester | 221–foaling | Rapid fetal growth and “real planning” phase | Prep foaling environment, tighten your calendar, increase monitoring as you enter the window |
If you don’t know the breeding date
Best ways owners can narrow the window
This happens all the time with pasture exposures, rescue mares, or “oops” situations.
Start with the simplest record you can trust. Write down the first and last day the mare could have been exposed to a stallion. Even a rough window is better than guessing one day.
If you have stallion turnout logs, texting history with a breeding farm, or any dated notes, use those to tighten the range. Owners often remember “the week we moved barns” or “right after the first frost,” and that clue can be enough to narrow your estimate by weeks.
Your veterinarian can also help confirm pregnancy and assess stage. The key is safety and accuracy, not trying to DIY a timeline from belly size alone. Mares carry differently, and abdominal shape is not a reliable calendar.
Even with an estimated date, you can still plan a reasonable window using the Horse Gestation Calculator.
Foaling window planning
30 days out
This is when you set yourself up for calm, not chaos.
Choose the foaling location and keep it consistent. Start thinking about how you will observe the mare, who is on call, and how you will reach your veterinarian quickly if something does not look right.
If you are moving barns or changing turnout routines, earlier is better. Big changes close to foaling tend to increase stress, which is the opposite of what you want.
14 days out
Now you tighten the plan and remove friction.
Confirm who is watching and when. Make sure your mare can be safely brought in, handled, and checked without drama. If she is anxious about being stalled, work that out now, not the night she decides to foal.
This is also a good time to do a “lights on” test. Walk the route you will take at 2 a.m. in bad weather. If the gate sticks or the aisle is dark, fix it now.
If you want a simple system for the final stretch, use the Complete Foaling Kit: 14 Day Watch Log, Newborn 24 Hour Protocol, and 1 2 3 Rule to track daily changes and stay consistent in the last two weeks.
7 days out
This is when you treat every day like it could be the day, but you keep your routine calm.
Increase observation frequency, especially at the times your mare tends to be most active or unsettled. Focus on meaningful changes, not random internet signs.
Meaningful changes are things like a clear shift in comfort, appetite, attitude, or how she moves. If you are unsure what “normal” looks like in your mare, go back to basics and keep a quick baseline record of temperature, pulse, and respiration so you have something real to compare. The Horse’s Vital Signs is a good reference for that.
Foaling window planning table (30, 14, and 7 days out)
Time before foaling | Your goal | What to do (simple and realistic) | Practical tip |
30 days out | Remove stress and friction | Choose foaling location, confirm vet contact plan, stabilize routine and turnout | Walk the barn route at night so you know what you’d do at 2 a.m. |
14 days out | Lock the plan in | Confirm who watches and when, make sure handling and stalling are smooth, adjust turnout or stabling if needed | Fix anything annoying now (sticky gate, dark aisle, missing halter) |
7 days out | Increase monitoring calmly | Check more often, watch for meaningful changes in comfort, appetite, attitude, and movement | Track a quick baseline so you can describe changes clearly if you call your vet |
Red flags during pregnancy (call your vet)
When to call right away
Pregnancy can look boring for months, and then change quickly. When something feels off, it is safer to call and be told it is nothing than to wait and hope.
Call your veterinarian promptly if you notice any of these:
Fever, sudden depression or refusing feed, colic signs, unusual vaginal discharge, sudden swelling that looks abnormal for your mare, premature dripping of milk, or signs that look like early labor.
If you like having a simple plan ready for the most stressful moments, keep our Colic Emergency Kit: First 2 Hours Response Guide and Monitoring Log on hand so you can track vitals and changes clearly while you wait for your veterinarian. If you are not sure what normal vitals should look like, review The Horse’s Vital Signs so you can give your vet clear information.
If you suspect fever, use Fever in Horses: Temperature Chart, Red Flags, and What to Do to confirm your temperature check and know when it is urgent.
FAQs
How long are horses pregnant on average?
Most mares carry for about 11 months, commonly in the 320 to 370 day range. The best way to plan is a window, not a single due date.
Can a mare go overdue and still be normal?
Yes. Some mares routinely carry longer, especially depending on season and individual history. If your mare seems comfortable and normal, your veterinarian will usually advise monitoring within a window rather than panicking about one calendar date.
What affects a horse’s gestation length the most?
The biggest practical drivers are the mare herself (her history and consistency) and the season the mare was bred. Breed can play a role, but it is usually a smaller influence than people think.
How early can a foal be born and survive?
This depends on how early and the foal’s maturity, and it is a veterinary question. If you suspect early labor or anything that looks abnormal, call your veterinarian immediately rather than trying to estimate viability at home.
What if my mare was bred multiple times?
Use the first and last possible breeding dates to create an exposure window. Then plan foal watch around that range instead of a single day. If you want a quick estimate, use the Horse Gestation Calculator.
When should I start foal watch?
Start light monitoring well before the due date, then increase observation as you enter the expected window. Your mare’s history matters. If she tends to foal early or late, use that pattern to adjust your plan.
Should I change feed during pregnancy?
Avoid sudden changes. Keep your mare in consistent, appropriate body condition and adjust gradually as needed. If you want a simple foundation refresher, use The Basics of Equine Nutrition and coordinate any bigger changes with your veterinarian.
How do I plan vaccines for a pregnant mare?
Use a risk based plan and align it with your breeding and foaling window. Start here: Vaccines hub.
If you want a quick explainer of common combo vaccines, read 5 Way Equine Vaccine: What It Covers and Why It Matters, then map your timing with the 5 Way Vaccine Planner.
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