Childhood and puberty

Compared to humans, rats have a brief, accelerated childhood. Rats develop rapidly during infancy and become sexually mature at about 6 weeks of age. Humans, on the other hand, develop slowly and don't hit puberty until about age 12-13 years (range: 8 to 16 years).

Adolescence and adulthood

Rats become sexually mature at age 6 weeks, but reach social maturity several months later at about 5 to 6 months of age (Adams and Boice 1983). In adulthood, each rat month is roughly equivalent to 2.5 human years (Ruth 1935).

Female rats enter menopause between ages 15 and 18 months (Durbin 1966), while humans enter menopause between 48 and 55 years (eMedicine).

Life expectancy

Domestic rats live about 2 to 3.5 years (Pass and Freeth 1993). In a survey of pet rat lifespans in the UK, the average lifespan was 21.6 months, and 95% percent had died by age 3 years (Clark 2004). In contrast, wild rats living in the wild tend to live for less than one year: 95% of wild rats die before age 1 year (Davis 1948).

The worldwide human life expectancy of humans is 66.7 years, but life expectancy varies a great deal between different countries. Human lifespan tends to correlate with economic development: people in the top 55 most developed nations have an average lifespan of 77.1 years, while people in the 33 least developed countries have an average lifespan of 49.4 years. In 2003, Japan had the highest life expectancy of 81.3 years, while Zambia had the lowest of 33.4 years (HD reports).

The rat's age in human years

Rat's age in months	Rat's age in years	Rat's age in human years
1.5 months (puberty)	0.125 years	12.5 years (puberty)
6 months (social maturity)	0.5 years	18 years (social maturity)
12 months	1 year	30 years
18 months	1.5 years	45 years
24 months	2 years	60 years
30 months	2.5 years	75 years
36 months	3 years	90 years
42 months	3.5 years	105 years
45 months	3.75 years	113 years
48 months	4 years	120 years