Gestation Horses Calculator

For AI or a hand mating, the date of service. For a pasture mating, the first day of exposure.
Use your own herd or breed average. 0 uses the published species figure.
Plus or minus this many days around the due date. 0 uses the published normal range if there is one.
Expected due date
2026-12-07
Animal Gestation Calculator
Due date falls on
Monday
What it is called
foaling
Gestation length used
340
Earliest expected
2026-11-17
Latest expected
2027-01-06
Shortest normal gestation
320
Longest normal gestation
370
Days pregnant today
256
Days to go
84
Gestation complete
75.29 %
Stage of gestation
final third of gestation
Species
Horse (mare)
Where the figure comes from
Mares are the most variable of the domestic species: anything from 320 to 370 days is within normal limits.
Worked out from Merck Veterinary Manual, The Reproductive System in Animals (gestation periods table) and 4 other sources.
A planning estimate from published mean gestation lengths, not veterinary advice. Individual animals, breeds, litter size and sex of the offspring all shift the date; confirm pregnancy and timing with your veterinarian.

How this is worked out

4 steps
  1. Horse (mare): published mean gestation of 340 days.
  2. 2026-01-01 + 340 days = 2026-12-07 (Monday), the expected foaling date.
  3. Normal range 320-370 days puts the window at 2026-11-17 to 2027-01-06.
  4. On 2026-09-14 the animal is 256 days into gestation, 84 to go.

Results are general information, not financial, tax, legal, medical or engineering advice.