Animal Gestation Calculator

Mouse Gestation Calculator

A mouse's gestation period is about 20 days, or roughly 0 months and 2 weeks, though it ranges from 19 to 21 days depending on breed and individual animal.

How to use the mouse 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 20-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.

Calculate a pup due date

What do you know?

Estimated birthing date

Friday, 2 October 2026

Earliest

1 Oct 2026

Latest

3 Oct 2026

20 days remaining0% complete

0 of 20 days elapsed

Milestone timeline

Key Mouse pregnancy milestones with calculated calendar dates
DayMilestoneDate
1Separate the male — a doe can conceive again within a day of birth13 Sept 2026
8Weight gain becomes detectable on a small digital scale20 Sept 2026
12Belly becomes obviously pear-shaped; increase protein24 Sept 2026
16Final cage clean and extra nesting material28 Sept 2026
19Earliest normal birth — do not disturb the nest1 Oct 2026
20Expected birth2 Oct 2026
28Separate the litter by sex before they can breed10 Oct 2026

What to do next

How long is a mouse's gestation period?

The average is 20 days from breeding to birthing, about 0 months and 2 weeks. Anything between 19 and 21 days is normal, and a typical litter is 5-8 pups. Treat the calculated date as the middle of that window rather than a fixed appointment.

Mouse gestation table: breeding date to birthing date

Breeding dates one week apart with the matching birthing date at 20 days.

Twelve sample Mouse breeding dates and their calculated due dates
Breeding dateExpected birthing date
12 Sept 20262 Oct 2026
19 Sept 20269 Oct 2026
26 Sept 202616 Oct 2026
3 Oct 202623 Oct 2026
10 Oct 202630 Oct 2026
17 Oct 20266 Nov 2026
24 Oct 202613 Nov 2026
31 Oct 202620 Nov 2026
7 Nov 202627 Nov 2026
14 Nov 20264 Dec 2026
21 Nov 202611 Dec 2026
28 Nov 202618 Dec 2026

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 20 days to give the breeding date to book, plus the earliest and latest service dates that still land inside your window.

Mouse gestation calculator FAQs

How long is a mouse pregnant?

About 20 days, with a normal range of 19 to 21. It is one of the shortest mammalian pregnancies, so a suspected pregnancy needs the cage prepared immediately rather than next week.

Can a mouse get pregnant again right after giving birth?

Yes, within a day. A pair left together produces a litter roughly every three weeks, which is how a couple of mice becomes an unmanageable colony in a few months. Remove the male before the birth.

Can I handle newborn mouse pups?

No. Mice are much more sensitive than rats about nest disturbance, and handling pups or cleaning the cage in the first week commonly causes the doe to abandon or kill the litter. Wait at least a week, ideally ten days.

When do mouse pups need to be separated?

By four weeks, split into same-sex groups. Mice can breed from five to six weeks, so a mixed litter left together will start producing its own litters almost immediately.

How many pups does a mouse have?

Usually five to eight, though litters of ten or more occur. First litters tend to be smaller. Very large litters need the mother on a richer diet with food available at all times.

How do I tell whether a mouse is pregnant or just fat?

Weigh her every two days: a pregnant doe gains steadily and fast, while a fat mouse holds her weight. Pregnancy also shows as a pear shape concentrated behind the ribs, with visible nipples and, from about day 14, obvious nest building.

More gestation pages

Rodent gestation periods