Mare Gestation Calculator

How it works

Equine gestation averages about 340 days from the last breeding date — roughly 11 months — but anywhere from 320 to 370 days is normal. Two healthy mares bred the same day can foal weeks apart, so treat the due date as the middle of a window, not an appointment.

Several factors nudge the timing: colts are often carried a few days longer than fillies, ponies tend to foal a little earlier than large breeds, and mares due in early spring often carry longer than mares due in summer.

Call your vet if a mare shows foaling signs before day 320 — foals born before ~320 days are premature and need immediate care — or passes day 370 with no signs. Most foalings happen at night and take under 30 minutes of active labor once the water breaks.