Browser-local date calculator · C399
Horse Gestation Calculator
Estimate a mare's approximate foaling date and broad typical range from a breeding date.
Enter the date
Estimated dates
The local calculator is initializing.
Method and sources
The default uses 340 days and shows the source-backed 330–370 days range. Dates are handled as Gregorian civil dates without timezone conversion. Penn State Extension is the timing source used for this page.
Worked example
A breeding date of 2026-01-01 plus 340 days gives an estimated typical date of 2026-12-07.
Limitations
These are planning estimates, not guaranteed birth dates or medical thresholds. Species, breed, individual animal, litter or fetal factors, and uncertainty in the starting event can change actual timing. Contact a veterinarian for animal-specific questions.