Rat Gestation Calculator
Last updated
A rat's gestation period is about 22 days, or roughly 0 months and 3 weeks, though it ranges from 21 to 23 days depending on breed and individual animal.
Calculate a pup due date
Estimated birthing date
Wednesday, 18 November 2026
Earliest
17 Nov 2026
Latest
19 Nov 2026
0 of 22 days elapsed
Milestone timeline
| Day | Milestone | Date |
|---|---|---|
| 1 | Separate the buck — a doe can conceive again immediately after birth | 28 Oct 2026 |
| 10 | Weight gain and firmer belly become detectable on a kitchen scale | 6 Nov 2026 |
| 14 | Increase protein: extra egg, cooked chicken or a breeding block | 10 Nov 2026 |
| 18 | Final cage clean and plenty of paper nesting material | 14 Nov 2026 |
| 21 | Earliest normal birth — leave the nest alone | 17 Nov 2026 |
| 22 | Expected birth | 18 Nov 2026 |
| 35 | Separate by sex — young rats can breed from five weeks | 1 Dec 2026 |
How to use the rat gestation calculator
- 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. Refine the inputs. The calculator uses the 22-day average for this species.
- 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.
| Breeding date | Expected birthing date |
|---|---|
| 27 Oct 2026 | 18 Nov 2026 |
| 3 Nov 2026 | 25 Nov 2026 |
| 10 Nov 2026 | 2 Dec 2026 |
| 17 Nov 2026 | 9 Dec 2026 |
| 24 Nov 2026 | 16 Dec 2026 |
| 1 Dec 2026 | 23 Dec 2026 |
| 8 Dec 2026 | 30 Dec 2026 |
| 15 Dec 2026 | 6 Jan 2027 |
| 22 Dec 2026 | 13 Jan 2027 |
| 29 Dec 2026 | 20 Jan 2027 |
| 5 Jan 2027 | 27 Jan 2027 |
| 12 Jan 2027 | 3 Feb 2027 |
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.