About the Gestation Calculator

Gestation is the period from conception to birth, and it varies enormously across species — from 31 days in rabbits to 640 days in elephants. The length tracks body size and evolutionary strategy: small mammals reproduce fast with short gestations and large litters, while large mammals invest months of pregnancy in a single, relatively mature offspring.

Practical use

Livestock farmers plan breeding calendars around gestation — a cow bred on July 1 is expected to calve around April 10 the following year (283 days). For dogs and cats, the window is tighter (58–68 days), and veterinarians often date pregnancy from ovulation rather than mating. This calculator adds the species-average period to your chosen date to give an expected due date, with the understanding that a few days of variation is completely normal.