How to convert a rat's age to human years? - briefly
A rat’s first year equals roughly 15 human years, and each additional year adds about 8 human years. Therefore, compute the equivalent age by assigning 15 years for the initial year and 8 years for every subsequent year (approximately 5 human months per rat month).
How to convert a rat's age to human years? - in detail
Translating a laboratory rodent’s lifespan into an equivalent human age provides a practical reference for biomedical research. The conversion relies on comparative biology: rodents mature rapidly, reach sexual maturity within a few weeks, and have a maximum lifespan of roughly two to three years, whereas humans achieve maturity over decades and may live beyond eight decades. These disparities shape the scaling factor used to map rodent years onto human years.
A widely accepted model expresses human equivalent age (HEA) as a function of the animal’s chronological age in years (RA):
- HEA = 16 × ln(RA) + 31
The natural logarithm (ln) captures the non‑linear acceleration of development in early life and the deceleration in later stages. The constant 31 aligns the adult rodent’s age with the average human adult age.
Applying the formula proceeds as follows:
- Record the rodent’s age in years (fractions accepted).
- Compute the natural logarithm of this value.
- Multiply the result by 16.
- Add 31 to obtain the human‑equivalent age.
For practical use, a short reference table illustrates typical conversions:
- 0.1 yr (≈5 weeks) → HEA ≈ 6 yr
- 0.25 yr (≈3 months) → HEA ≈ 12 yr
- 0.5 yr (≈6 months) → HEA ≈ 20 yr
- 1 yr → HEA ≈ 31 yr
- 2 yr → HEA ≈ 45 yr
These values demonstrate rapid early development, after which each additional rodent year adds roughly 14 human years.
Limitations of the model include strain‑specific lifespan variations, environmental influences, and the fact that the equation derives from median survival data rather than individual health status. Consequently, the conversion offers an approximate, not exact, correspondence and should accompany other physiological markers when interpreting experimental outcomes.