Animal Gestation Calculator

Horse Gestation Calculator

A horse's gestation period is about 340 days, or roughly 11 months, though it ranges from 320 to 370 days depending on breed and individual animal.

How to use the horse gestation calculator

  1. 1. Choose what you know. Enter the breeding date to get a due date, or switch to the target due date mode to work backwards to the breeding date you need.
  2. 2. Refine the inputs. The calculator uses the 340-day average for this species.
  3. 3. Plan around the range. Use the earliest and latest dates and the milestone timeline to schedule checks, feed changes and preparation of the foaling area.

Calculate a foal due date

What do you know?

Estimated foaling date

Wednesday, 18 August 2027

Earliest

29 Jul 2027

Latest

17 Sept 2027

340 days remaining0% complete

0 of 340 days elapsed

Milestone timeline

Key Horse pregnancy milestones with calculated calendar dates
DayMilestoneDate
16Ultrasound to check for twins28 Sept 2026
300Increase feed, begin foaling prep9 Jul 2027
320Move to foaling stall, remove Caslick if present29 Jul 2027
340Expected foaling18 Aug 2027

What to do next

How long is a horse's gestation period?

The average is 340 days from breeding to foaling, about 11 months. Anything between 320 and 370 days is normal, and a typical litter is 1 foal. Treat the calculated date as the middle of that window rather than a fixed appointment.

Horse gestation table: breeding date to foaling date

Breeding dates one week apart with the matching foaling date at 340 days.

Twelve sample Horse breeding dates and their calculated due dates
Breeding dateExpected foaling date
12 Sept 202618 Aug 2027
19 Sept 202625 Aug 2027
26 Sept 20261 Sept 2027
3 Oct 20268 Sept 2027
10 Oct 202615 Sept 2027
17 Oct 202622 Sept 2027
24 Oct 202629 Sept 2027
31 Oct 20266 Oct 2027
7 Nov 202613 Oct 2027
14 Nov 202620 Oct 2027
21 Nov 202627 Oct 2027
28 Nov 20263 Nov 2027

Working backwards from a target foaling date

If you want foals on the ground in a particular week, switch the calculator to target date mode and enter the date you are aiming for. It subtracts 340 days to give the breeding date to book, plus the earliest and latest service dates that still land inside your window.

Horse gestation calculator FAQs

How long is a horse pregnant?

A mare is pregnant for about 340 days, roughly 11 months. Anything from 320 to 370 days is considered normal, so the calculated date is a midpoint rather than a deadline.

Why is the foaling date so unpredictable?

Foaling is triggered by foetal maturity rather than a fixed clock. Season, mare age, foal sex and nutrition all shift the date, which is why the normal range spans about seven weeks.

Is a foal born before 320 days viable?

A foal born before about 320 days is premature and needs immediate veterinary care. Survival improves considerably after 330 days, when the lungs and immune transfer are more mature.

When should I check for twins?

Ultrasound at days 14 to 16 is standard. Twin pregnancies rarely produce two healthy foals and often end in late abortion, so one embryo is normally reduced at that scan.

What are the signs foaling is imminent?

Udder filling weeks ahead, waxing of the teats one to two days before, milk that turns opaque and calcium-rich, relaxed tail head and restlessness. Most mares foal at night.

Should I change the mare's feed in late pregnancy?

Yes. From about day 300 the foal's growth is rapid, so increase energy and protein gradually and keep mineral and vitamin intake balanced. Avoid sudden ration changes at any stage.

More gestation pages

Livestock gestation chart