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Rat Gestation Calculator
Rat pregnancy uses 22 days in this calculator, with a 21 to 23 day planning window after mating. Enter the mating date below.
Rat gestation at a glance
| Average used by this calculator | 22 days (about 3.1 weeks) |
|---|---|
| Window shown by this calculator | 21 to 23 days after breeding |
| Due date formula | Breeding date + 22 days |
| Young | Pups |
| Usual litter | 8 to 18 pups in Merck owner guidance |
Merck says pregnancy may be noticeable after about two weeks through weight gain or mammary development. A female mated right after giving birth may have delayed implantation during nursing, so delivery may fall outside this calculator's planning window.
Rat breeding and birth timeline
| Mating date | The calculator starts with the entered mating date. |
|---|---|
| About 2 weeks | Pregnancy may be noticeable by weight gain or mammary development. |
| Days 21 to 23 | Merck gives this as the usual rat gestation period. |
| After birth | Merck says rat pups are born deaf and blind. |
| About day 21 after birth | Weaning usually occurs around this age. |
Frequently asked questions
How long is a rat pregnant?
The rat calculator uses 22 days after mating and a 21 to 23 day planning window, matching Merck's usual range. A female mated right after giving birth may have delayed implantation during nursing and deliver later.
How do I calculate a rat due date?
Enter the mating date and the rat calculator adds 22 days for an estimated pup due date and shows its planning window.
What are newborn rat pups called?
Merck calls baby rats pups and says they are born deaf and blind; typical litters contain 8 to 18 pups.
When should I call a veterinarian during rat birth?
If rat birth appears abnormal, contact a veterinarian promptly.
Sources
- Merck Veterinary Manual: Breeding and Reproduction of Rats
- Merck Veterinary Manual: Mice and Rats As Pets
Reviewed by Elliott Garber, DVM · Last reviewed
