What is the basis for rat-to-human age conversion?

The calculator uses the piecewise scaling published in Sengupta (2013) Int J Prev Med. Rats age at ~87–139 human days per rat day during early development, slowing to ~30 human days per rat day through middle age and ~25 per day in senescence.

How does the rat model differ from the mouse model?

Rats live ~30 months (vs ~26 months for mice), reach puberty at a similar time (~6 weeks) but have different piecewise scaling ratios. A 12-month rat is ~30 human years, while a 12-month mouse is ~38 human years — rats age more gradually after adolescence.

How does strain choice affect the result?

Sprague-Dawley is the reference strain at ~30 months median lifespan. Fischer 344 is shorter (~27 months, factor 0.90), Brown Norway is longer (~33 months, factor 1.10). The strain factor adjusts lifespan position but does not change the human-age conversion.

When is a rat considered middle-aged or senescent?

For Sprague-Dawley rats, middle age spans 12–24 months (~30–60 human years). Senescence begins at ~24 months. Most aging studies use 18-month rats as the "middle-aged" cohort and 24-month rats as the "aged" comparator.

Can I compare rat ages directly to mouse ages?

Yes — use the Lab Animal Age Converter for cross-species comparison. It converts both species to human-equivalent years as a common denominator, then shows the equivalent age in each species side-by-side.

ToolsConductScience tool

Rat Colony ManagementFree in-browser calculator

Rat Age Converter.

Convert rat age to human-equivalent age using Sengupta (2013) piecewise scaling. Strain-specific lifespan factors for Sprague-Dawley, Wistar, Fischer 344, and more.

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Need cross-species comparison? Try the universal Animal Age Converter

Rat Age

Age value

Unit

Strain

Conversion

Rat age

84 d

12.0 wk · 2.8 mo

Human-equivalent

14.5 human years

Sengupta (2013)

Life stage

Young adult (6 wk–6 mo)

Strain Sprague-Dawley

Lifespan position

of strain median

Position on Strain Lifespan

NeonatalPre-weaningJuvenileYoung adultMature adultMiddle-agedSenescentMedian

When to use

Labeling rat cohort age in human-equivalent terms for translational papers
Choosing the right developmental window for juvenile or adolescent rat studies
Comparing aging-study cohorts across labs using different strain conventions
Justifying cohort age in IACUC and grant applications for rat studies
Communicating rat cohort age to clinical collaborators

Do not use for

As a biological-age estimate — use epigenetic clocks for that
For genetically-modified strains with altered lifespan (e.g. Zucker obese rats)
For non-rat species — use the Lab Animal Age Converter for mouse or zebrafish

Rats mature slightly differently than mice

Despite similar weaning age (~21 days), rats and mice have different piecewise ratios. Do not use mouse scaling tables for rats — the human-equivalent ages diverge significantly by 12 months.

Strain lifespan factors do not change human-age math

A 12-month Fischer 344 rat has the same human-equivalent age as a 12-month Sprague-Dawley rat. The strain factor only adjusts where each sits on its lifespan curve.

NIA Aged Rodent Colony uses Fischer 344 and Brown Norway

If you receive rats from the NIA colony, select the appropriate strain in the calculator for accurate lifespan positioning.

Method

Rat age (days) is converted to human-equivalent days via a piecewise function calibrated against published anchor points from Sengupta (2013). Lifespan position = rat_days / (median_lifespan_days × strain_factor). Strain factors are taken from published median lifespan data for common laboratory rat strains.

Validated

Last validated 2026-04-09. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.

How to cite

How to Cite

ConductScience Rat Age Converter (v0.87.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/rat-age-converter

Sengupta P. The Laboratory Rat: Relating Its Age With Human's. Int J Prev Med. 2013;4(6):624-630.

Sengupta (2013) Rat-Human Age Scaling

The piecewise model used by the calculator:

Days 1–21 (pre-weaning): ~87 human days per rat day
Days 21–42 (juvenile, weeks 3–6): ~139 human days per rat day
Days 42–182 (young adult, 6 wk–6 mo): ~13 human days per rat day
Days 182–365 (mature adult, 6–12 mo): ~24 human days per rat day
Days 365–730 (middle-aged, 12–24 mo): ~30 human days per rat day
Days >730 (senescent): ~25 human days per rat day

Key anchor points: rat 6 weeks ≈ human 13 years (puberty), rat 6 months ≈ human 18 years, rat 12 months ≈ human 30 years, rat 24 months ≈ human 60 years.

Rat Aging in Translational Studies

Rats are the preferred model over mice for many aging studies because of their larger brain size, more complex behavior, and better pharmacokinetic modeling. The NIA Aged Rodent Colony provides Fischer 344 and Brown Norway rats at standardized ages.

Recommended aging cohorts:

Young adult: 3–6 months (~18–20 human years)
Middle-aged: 12–18 months (~30–45 human years)
Aged: 24–30 months (~60–75 human years)

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