Cow Heat Cycle Calculator — Next Heat Dates for Cows, Sows, Ewes, Goats & Mares

How it works

Next heat = last heat + cycle length (cow, sow, goat, mare ≈ 21 days; ewe ≈ 17 days) · Watch window = last heat + normal range (cow 18–24 days) · Expected birth = breeding date + gestation (cow 283, sow 114, ewe 147, goat 150, mare 340 days)

Cows, sows, does and mares cycle about every 21 days and ewes about every 17 days until they become pregnant. Marking the heat date and watching again 18–24 days later is the cheapest way to catch the next chance to breed — and the most reliable early sign that an insemination failed. Many cows show standing heat for only 12–18 hours, often at night, so check at least twice a day, ideally morning and evening for 30 minutes each, and use tail paint or heat-detection patches.

Worked example

A cow seen in standing heat on October 1, 2026 is expected back in heat on October 22, 2026, 21 days later; watch her closely from October 19, 2026 to October 25, 2026. Use the AM–PM rule — a cow first standing in the morning is inseminated that evening. If she is bred and does not return, she would calve around July 11, 2027.

Sources: Mississippi State University Extension — The estrous cycle of cattle · University of Wisconsin — Animal Science 434: reproductive cycles in the female

Frequently asked questions