Determining the age of a rat can be tricky, but there are a few ways to get a rough estimate. Rats grow quickly in their first few months of life, meaning their size can be a good indicator of age early on. As they mature, other factors like coat condition, teeth wear, and overall health can provide clues. While it’s impossible to know the exact age, paying attention to these details can help narrow it down. Here’s an overview of what to look for at different life stages.
Newborn (0-14 days)
Newborn baby rats are called pups or kittens. At birth, they are tiny, weighing only around 5-6 grams and being about 2 inches long (not including the tail). They are born hairless with their eyes closed, only opening them at around 2 weeks old. Newborns are completely dependent on their mother and cannot eat solid food or regulate their own temperature until around 14 days old.
Pinkies (0-1 week)
The first week of a rat’s life when they have no fur and their skin appears pink is referred to as the “pinkie” stage. Pinkies rely entirely on their mother’s milk to survive. They are unable to see, hear, or even regulate their own body temperature at this point. By feeling the size and looking for key characteristics like closed eyes and ears, pinkies can easily be identified as newborns less than 1 week old.
Furring Up (1-2 weeks)
Around days 5-7, baby rats start to develop fine, downy fur. They are still very small at this stage, weighing 10 grams or less. Their eyes begin opening between days 12-14, starting off pale blue then transitioning to black over the next week. Ears also start to open and teeth begin coming in around day 10. Mobility increases as they start crawling around the nest.
Weanlings (3-5 weeks)
At 3 weeks old, baby rats begin the weaning process as they transition from milk to solid food. This is a good time to separate males from females to avoid unwanted litters. They continue to grow rapidly and explore outside the nest. Body fur comes in more, their adult coat patterning starts to show, and they reach around 30-70 grams in size.
Juveniles (6-10 weeks)
From 6-10 weeks is considered the juvenile stage. Rats achieve most of their adult size during this time, reaching up to 250 grams. Their coat is fully furred out but remains soft and sleek looking. They become quite active and inquisitive. You can estimate age in weeks during this period based on weight and overall body size.
| Age (Weeks) | Weight Range |
|---|---|
| 6 weeks | 70-100 g |
| 7 weeks | 100-150 g |
| 8 weeks | 150-200 g |
| 9 weeks | 200-250 g |
| 10 weeks | 250 g |
Young Adults (3-5 months)
From 3-5 months of age, rats are considered young adults. Their full adult coat will come in completely by 3 months. Young adults remain energetic and playful. Females may go into heat cycles starting around 5 weeks old and can become pregnant from 3 months onward. For males, testicles descend visibly into the scrotum by 5-6 weeks old.
Adults (6 months to 2 years)
After 6 months, rats are mature adults. Females may continue regular heat cycles and breeding until around 18 months old. Weight can help determine age within the adult range:
| Age | Average Weight Range |
|---|---|
| 6 months | 250-500 g |
| 1 year | 300-550 g |
| 18 months | 350-600 g |
| 2 years | 400-650 g |
Other age indicators in adults include:
- Coat becoming coarser and scruffier
- Teeth showing wear and yellowing
- Greying fur especially around the face and shoulders
- Hunched posture
- Reduced activity levels
- Increased incidence of health issues
Seniors (over 2 years)
Rats over 2 years old are considered senior or geriatric. Average lifespan is around 2-3 years, but some rats live up to 4 years. Indications of old age include:
- Very scruffy, patchy coat
- Excess porphyrin staining around eyes/nose
- Catheterization lesions on the skin
- Hind limb weakness
- Enlarged abdomen
- Lumps or tumors
- Tooth loss
- Very low energy and activity
Conclusion
Estimating a rat’s age takes some detective work, but looking at multiple factors like size, coat, teeth, and health provides clues. Key stages include newborn, juvenile, adult, and senior. Within adulthood, weight estimates can help gauge a 1-2 year range. While not exact, paying attention to these details allows a reasonable guess at a pet rat’s age.