I won’t keep you in suspense, one rat day is equal to 34.8 human days!

If there’s one thing most rat owners know, it’s that rats do not live long enough 🙁

If that’s all you wanted to know, you’re welcome, I created no suspense and didn’t keep you waiting; you may continue on with your day 😉

Stick around if you’d like to know what factors were taken into consideration to come to this conclusion.

A 2013 study published in the International Journal of Preventive Medicine reviewed over 40 studies on how rats age and concluded that in one human day, rats age more than one month.

I knew I loved and cherished my rats anyway, but this knowledge puts their short lives into even more perspective!

The Rat Studies

Pallav Sengupta’s review reported something we learned in last week’s blog post, which is that rats grow rapidly, and do most of their growing in their first few months of their lives.

The studies reviewed were largely carried out on Wistar rats, the albinos that are close cousins of our beloved pets.

lab rat fancyrat rats pet rats pocket pets

It also reported that rats become sexually mature at only six weeks old, and by five or six months have reached social maturity.

This is about the time we start to see males in particular assert themselves and if they’re inclined to want to be alpha, they’ll start jostling for the top spot.

Many of us can relate to the stress and struggles (and desexing expense/stitch removal troubles!) around this period of their lives eeeek!

Due to the biological differences between rats and humans it’s not sufficient to simply compare the average lifespan of a human (80 years) to that of a laboratory rat (2.5-3 years).

Sengupta reported that that equation would make one rat day relative to just under 14 human days and if only that were correct, we’d have our babes around for at least double the time we currently do!

The Discarded Methods of Age Determination

Scientists tried to determine the comparative age of rats in many ways and the abridged version of them are:

  • Eye lens weight – mammalian lens weights increase over time/with age and is generally considered an accurate indicator.  However with rats the lens weight only proved to be accurate up to 3-4 months old (again, when the rat does most of it’s growing as discussed last week!).
  • Teeth – those big front teef your rats have are reportedly a very good test of age.  At around 2.5 months old, the crown of the teeth are pushed upwards by the growth of roots so by the time a rat is old, there is mostly root and very little crown.  Sengupta finds this an unreliable method due to “differences in diet and…primary molar hardness, molar wear may differ geographically”.
    I could be wrong about the front teeth being the molars Sengupta is referring to – it seems to be, although they are technically called incisors according to my research.
  • Endosteal layers in the tibia – counting these tibial layers is reportedly another good method for estimating age, however the young rodents have thrown a spanner in the works again!  More layers can be counted in the early months of rats than their age.
  • Bone formation – the study of bone formations is a reliable technique for age determination in humans because over a life span a lot of changes take place.  Rats either don’t live long enough for those changes to take place, or they simply don’t happen in our fancy friends.

So What are Reliable Indicators of a Rat’s Age then?

Sengupta worked out that rats age at different rates during different phases of their bioligical lives.

I recommend giving the study a read from “Rat age and human age: Revealing the revelation” because there’s a lot of bloody interesting stuff in there, and for those that couldn’t be bothered, I’m sure to write up a post about it in the future.

The crux of it is, the following phases of development (and how they compare to those same phases in humans) are taken into consideration when calculating a rat’s true age, and they age differently in each cycle:

  • When babies are weaned.
  • When the young hit puberty.
  • When they reach sexual maturation (interesting find! Rats reach sexual maturity at 38 days old,12 days earlier than they hit puberty!).
  • When they go through adolescence.
  • When they reach adulthood.
  • When they each cease to be fertile.
  • The period between fertility and death.

Sengupta stated that “although rats are indispensable elements of biomedical research [cue depressive thoughts] differences in biology, anatomy, physiology, development and bilogical phenomena must be taken into consideration when analyzing the results of any research in rats where age is a crucial factor”.

But we didn’t really need more convincing that animal testing isn’t all it’s cracked up to be; that’s just scraping the surface of it!

Here’s a handy dandy table I graciously saved and inserted for your skimming pleasure!

rat faction, rats, pet rats, exotic pets, how old are rats compared to humans


This study is five years old, but a good one, because it reviewed 42 studies into the age of rats.

Sengupta has broken down the ageing process (and given equations for those among us who love a bitta maths!) into the cycles of life we all, as mammals go through.

Rats age at different rates during each phase of their life, and hooo do they age fast during weaning!

My rats Floki and Basil lived to between approximately 90 and 105!  We dun good 🙂

What’s the longest lived rat you’ve had?

This community is nothing without your input!  Comment, join in and if you’ve got a story you’d love to share, please pitch it through the contacts page!


Pallav, S. 2013, ‘The laboratory rat: relating its age with human’s’, International Journal of Preventive Medicine, vol 4(6) pp. 624-630,  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3733029/



Melanie is a freelance copywriter, blogger and rat fan!You can hire her to write words that suit your purposes and achieve your goals, just shoot her an email through the Contacts page.
Melanie shares her flat with two female ginger cats and occasionally some ants.

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  1. This is super interesting! My oldest girl is 2.5 now, it’s makes sense that she’s slowing down a bit! I will be too at 75!

    1. 2.5 is roughly the average age females live to, so if she’s just slowing down now I’d say she’s got some time to go yet! When you think about how old a rat is in human years, some things are really put into perspective aren’t they lol XD

      Like slowing down and getting plump hehee.

  2. Love all this information!
    My oldest rat so far was 2 ¾ years old. But I believe Lily, my current oldest resident must be closer to 3. She was at least 5 or 6 months old when I adopted her more than two years ago. What’s even more amazing is how she is still such a tough little cookie after so many health struggles. Two tumour removals (a third one recently popped up, but we have decided against surgery this time), a stroke, a facial abscess, HLD and of course the odd URI or UTI, just to keep things interesting. She is such a fighter and I love her to bits 💖

    1. Lisa, Lily is a super rat! I can very much relate. I’ve had several rats that have had numerous health conditions and kept going (with veterinary intervention and my undying commitment to medicating 1400 times a week lol)! I have removed every single bump on all of my rats, except one. He had a malignant tumour which was removed twice. It was only on the second time that the vet said it’s malignant (and he wouldn’t have removed it/scraped it a second time had he known, rude!). The two removals bought us all an extra two months and the operations were worth the expense for the time we had together. He was three when he had those ops! The third time it grew it was his time and I knew I couldn’t put him through a third op anyway, it was pointless and he was too tired.

      My oldest lived rat Floki, had two operations while he was three and a couple while he was over 2.5. They are such tough buggers! Good luck to your beautiful Lily, I hope her tumour grows very slowly so you have a lot more time together x

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