How old is my dog in human years?

By Dr Rebecca MacMillan BVetMed BSAVA PGCertSAM MRCBS

‘How old is my dog in human years?’ – a question that many owners ask, and not a straightforward one to answer! While rough estimates can be given, no equations are 100% accurate as the ageing process between different dogs is so variable. Let’s take a look in more detail…

Dog years vs human years

A lot of people think that one human year is equivalent to seven dog years, however it’s more complicated than that. Different sized dogs live different amounts of time which can affect the maths. Plus, dogs go through some of their developmental periods much more rapidly than we do, for example the time it takes for them to go through puberty.

Instead of the seven-year rule, the American Veterinary Association and the American Kennel Club calculate age as follows –

1. The first year of a medium-sized dog’s life is equivalent to 15 human years
2. The second year is equal to about 9 human years
3. Then each year thereafter is worth 5 human years

This gives us a good rough approximation to go on.

However, a recent study used a more complicated equation based on DNA methylation. This more accurately looks at how genes and their expressions become changed over time. These mathematical models give us a ‘molecular clock’ which helps us to more accurately predict ageing.

The researchers developed the following equation to calculate a dog’s age in human years based on this information: human age = 16 ln(dog age) + 31. The abbreviation “ln” stands for the natural log.

Their comparison of age in dogs and humans is as follows -
Dogs' Age	Humans' Age
First 8 weeks	First 9 months
2 - 6 months	1 - 12 years
6 months - 2 years	12 - 25 years
2 - 7 years	25 - 50 years
7 - 12 years	70 years

The drawback is that this study focussed on a single breed, the Labrador, so it may not match up to your own dogs ageing. However, it is good to know that more accurate ways of ageing dogs are being researched in this way.

This project also highlighted that dogs enter middle age much earlier than we might expect, giving them a longer period of ‘older age’ than previously thought. This is important when thinking about age related diseases and health conditions in our pets.

How can I tell how old my dog is?

If your dog is a rescue, then you may not know how old they are. Unfortunately, it is not possible to age your dog with any accuracy, but a vet may be able to give a rough indication based on -

1. Dental health – discolouration, tooth wear and tooth loss can be age indicators, but dental health is also affected by diet and genetics.
2. Coat condition and colour – a dull or greying coat is more likely in older pets
3. Mobility – changes in the way the dog moves occur as they age
4. Eye condition - cloudiness or vision issues can indicate advancing age
5. Body shape - signs of muscle wastage and the development of fat pads can indicate older age

Dog Age Chart

There are a variety of different tables and estimates out there but this one was produced by The American Animal Hospital Association to give an estimate of human physiological age for different sizes of dog.

Dog in years	Age in Human Years for Small Dog (20 pounds/9kg or less) in human years	Age in Human Years for Medium Dog (21-50 pounds/9.5 – 22.7kg)	Age in Human Years for Large Dog (51-90 pounds/23.1kg -40.8kg)	Age in Human Years for Giant Dog (90+ pounds/40.8kg+)
1	15	15	15	15
2	24	24	24	24
3	28	28	30	32
4	32	33	35	37
5	36	37	40	42
6	40	42	45	49
7	44	47	50	56
8	48	51	55	64
9	52	56	61	71
10	56	60	66	78
11	60	65	72	86
12	64	69	77	93
13	68	74	82	101
14	72	78	88	108
15	76	83	93	115
16	80	87	99	123
17	84	92	104	–
18	88	96	109	–
19	92	101	115	–
20	96	105	120	–

When is a dog considered old?

A dog is considered to be old or ‘senior’ when they reach the last 25% of their expected breed lifespan. Most dogs reach their senior years somewhere between 7 and 12 years of age, with smaller dogs having a longer period of adulthood than giant dogs. So, at 7 years old, a Yorkshire Terrier will still be relatively active and youthful, whereas a Great Dane will be considered a senior.

How long will my dog live?

Lifespan varies between different sizes of dogs. As a general rule, smaller dogs tend to live for longer than large or giant breeds, with average lifespans as follows –

1. Small dogs: 10-15 Years
2. Medium dogs: 10-13 Years
3. Large Dogs: 10-12 years
4. Giant Dogs: 8-10 years

Your dog’s lifespan will depend on several other factors including breed, genetics, health status, and nutrition.

 What do I need to know as my dog gets old?

As your dog gets old, they may become more susceptible to certain health complaints. Regular vet checks are essential to spot these problems early. Common senior health complaints include –

1. Dental disease
2. Joint disease e.g. osteoarthritis
3. Cancer
4. Heart disease
5. Diabetes mellitus
6. Obesity
7. Kidney disease
8. Cognitive dysfunction
9. Hearing and vision loss
10. Digestive disturbances

Many of these conditions can be treated or well-managed with the right veterinary care. Your Vet may recommend dietary changes, medication or the use of supplements (such as DotDotPet's Multifits) to help support your aging dog

As well as regular checkups, there are plenty of things you can do to support your senior pet at home. Why not take a look at our senior dog care article for inspiration?

Summary

Ageing dogs accurately is a tricky business! But research is ongoing, so more accurate methods could be just around the corner. Meanwhile, providing your senior pet with the care and attention they deserve should be your number one priority. Always speak to your vet if you have any concerns about your dog’s age or health status.