Rat Gestation Calculator

How to use the rat gestation calculator

1. 1. Choose what you know. Enter the breeding date to get a due date, or switch to the target due date mode to work backwards to the breeding date you need.
2. 2. Refine the inputs. The calculator uses the 22-day average for this species.
3. 3. Plan around the range. Use the earliest and latest dates and the milestone timeline to schedule checks, feed changes and preparation of the birthing area.

How long is a rat's gestation period?

The average is 22 days from breeding to birthing, about 0 months and 3 weeks. Anything between 21 and 23 days is normal, and a typical litter is 6-12 pups. Treat the calculated date as the middle of that window rather than a fixed appointment.

Rat gestation table: breeding date to birthing date

Breeding dates one week apart with the matching birthing date at 22 days.

Working backwards from a target birthing date

If you want pups on the ground in a particular week, switch the calculator to target date mode and enter the date you are aiming for. It subtracts 22 days to give the breeding date to book, plus the earliest and latest service dates that still land inside your window.