Foaling date calculator
Pick the date your mare was covered. You get her likely foaling dates, the full normal range, and how many days along she is today.
Pick the date the mare was covered and the dates appear here.
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How long is a mare pregnant?
Longer than people expect. A US extension guide written by Kathy Anderson, Extension Horse Specialist at the University of Nebraska, puts it plainly: "The average gestation length (duration of pregnancy) of mares is 335 to 340 days, but can range from 320 to 370 days."
That is a wide window. Day 320 and day 370 are seven weeks apart, so the calculator gives you both ends as well as the average.
How it works
It counts days on from the covering date. Covered on 1 May 2026, a mare's average window is 1 to 6 April 2027. Her normal range runs from 17 March to 6 May 2027.
The same guide adds: "There may be much variability among mares, but most individually follow similar patterns year after year." So if your mare has foaled before, her own past pregnancies are worth a look too.
If she was covered more than once, try the first and the last date and look at both answers.
Sources
Kathy Anderson, Management of the Pregnant Mare, Extension Horses, 31 January 2020. Read 30 October 2026.