Rat years to human years: How old is my rat? - RatCentral

Rat years to human years: How old is my rat?

More than likely, you’ve heard of dog years. You know the formula: one dog year equals seven dog years. You’ve heard dog owners talk about their pets being “teenagers” or “middle-aged.” But, if you’re a rat owner, of course the same calculation doesn’t work. So how old is your rat, in comparable human years? How much linear time is equal to one rat year?

The “pet years” calculations

To begin with, let’s talk about what people really mean when they talk about dog years, cat years, or rat years. Simply put, “pet years” are just a way to compare the average animal lifespan to the average human lifespan. Most calculations are a matter of simple algebra. They do not take into account the stages of development in the relevant animal; to do so would require much more complex calculations, since animals and humans do not reach crucial stages of development at comparable times. For instance, a particular animal may reach social maturity at ⅛ of its lifespan, whereas humans reach social maturity at about ¼ of their lifespan. 

“Pet years” calculations, then, are just a way to estimate how old their pet would be if it had lived its life as a human. For instance, the average dog lives between 11 and 12 years, while the average human lives nearly 80 years. So, to calculate “dog years,” you simply divide 80 years by 11.5 years, which gives you the magic and much-quoted number of seven. This means that for every one linear year a dog lives, it has aged as much as a human would age in seven years.

In the end, these calculations don’t mean a ton. Mostly, they’re simply a way for humans to understand what proportion of their life their pet still has ahead of them. And, there’s an inherent adorableness in thinking of your pet as a moody teenager or a slumped middle-aged man. When talking about rat years to human years, these calculations don’t correlate to the stages of development in your rat (such as social or sexual maturity). Instead, rat years refers only to the proportion of life your rat has lived in comparison to the average, expected lifespan of rats. 

Rat years to human years

Because there is a wide variation in the life expectancy of domesticated rats, there is a bit of disagreement on how many human years equal one rat year. However, in general, it is estimated that one day in a rat’s life equals approximately 35 human days. This means that one month in a rat’s life equals between 2.5 and three human years.

You can double check this calculation on your own. The average domesticated rat lives between two and 3.5 years, which for this calculation we can estimate as 2.75 years. In comparison, the average human lives 79 years, which we’ll round up to 80 years for simplicity’s sake. Simple divide the 80 human years by the 2.75 rat years, and you get approximately 29 years. That means that in one year, your rat ages the same amount that you would age in 29 years. Because this is such a large number, we can further divide it out into months. Dividing 29 years by the 12 months in a year, we get 2.4. This means that your rat — if it were to live for 2.75 years — ages in one month the same amount that you age in 2.4 years. This calculation is fairly close to the numbers cited by scientific articles. The slight differences between the two calculations can be accounted for by the variation in rats’ lifespans, which will affect the ultimate comparison of rat years to human years. 

Your rat’s stages of development

Now you know how much your rat ages in comparison to yourself, but this calculation doesn’t account for your rat’s stages of development. Simply put, your rat may be the equivalent of 20 years old based on the previous calculation, but this doesn’t mean that their social or sexual maturity level is comparable to a human 20-year-old’s. 

There are a few key stages of development that your rat will go through in its lifespan. To begin with, your baby rat will open its eyes and start being adventurous at about two weeks old. By five weeks, your rat is growing quickly, and you’ll start be able to see a size difference between male and female rats. At about six weeks old, your rat will reach sexual maturity, which means that the male and female rats of a litter need to be separated. At this age, your rat is ready to go home to your house, and be separated from its mother and siblings. However, your rat still has a few months after that before reaching social maturity, which is usually at about five to six months old. At this point, your rat has reached full maturity and is considered an adult rat by all measurements.

Longest living rats and average life spans

Part of the reason that determining the rat years to human years conversion is that rats have a wide variation of lifespans. Domesticated rats, commonly called fancy rats, range in average lifespan from two years to 3.5 years. According to some estimates, however, only five percent of domesticated rats make it to or past three years old. In comparison, 95 percent of wild rats don’t live to a full one year old, which is clearly a much shorter lifespan than a fancy rat. The oldest recorded domesticated rat, though, lived for seven years and four months. Anecdotally, many rat owners report their rats living for four or even five years, making it clear that the average doesn’t always apply. 


In general, it’s a fairly accurate estimate to say that one month in a rat’s life is the equivalent aging time to 2.5 human years. Although this number has no bearing on your rat’s developmental stages, it’s an easy and entertaining way to compare your rat’s age to your own age. Though a rat’s average lifespan is only a few years, keep in mind that there are many exceptions to that rule, and your rat may be the next to break the record!

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