Mare Gestation Calculator - Horse Gestation

The calculator uses a typical gestation length and a reasonable range:

Where $M$ is the mating date and $D$ is the estimated foaling date.

1. Enter the mating date to get the estimated foaling date.
2. Or enter a foaling date to estimate the corresponding mating date.
3. Use the Earliest and Latest dates as a practical range.
4. The result card also shows how many days are left (or how many days past due).

This calculator uses 338 days as an estimated gestation length, with a range of 331–346 daysto reflect typical variation. Individual mares can vary.