Gestation Calculator

Ok, for those of use that are lazy or don't do math in our heads! Feel free to use this handy little calculator to help you predict due dates and other important dates regarding pregnancy of the mare. You may have to open this page in Internet Explorer to get it to work.

Type your information into the yellow cells by clicking in the appropriate yellow cell. You may have to hesitate and then click again before it will let you type.  Type your dates in this format:  dd/mm/yyyy.  For example, June 10, 2007 would be 06/10/2007.

Each time you press your Enter key after typing information in, the new results will be calculated automatically in the gray cells.

Click here to open the calculator separately in Microsoft Excel or other spreadsheet.

Or, fill in here if your browser shows the interactive chart (best viewed in Internet Explorer):

If you aren't comfortable with the above interactive table or the downloaded one from here, try this printable chart: http://www.equine-reproduction.com/articles/340daychart.htm

"Is My Mare Past Due?"

This is a common question mare owners have when their mare reaches 340 days without foaling. It should be noted with confidence that the due date of the mare is NOT 340 days after her last breeding! The average gestation of mares is anywhere from 320 to 370 days. NOT 340 days. The 340 is a magical number that represents the average gestation of average mares. It is not a date that, once passed, should raise concern on the part of the mare owner.

Here are our gestations from our mares for the last 3 or 4 years, for example. Note that one mare's gestation was 373 days, and her foal was fine and normal in size!  If we had induced labor with her at 350 days, her foal would probably have been premature. Also, nearly half of our foals have been born after 340 days of gestation.