How to Tell How Old a Puppy Is? (Teeth Method Explained)

Let’s say you’ve found a stray or have been given a mystery puppy by someone, you are going to want to know a way to tell how many weeks old the puppy is. As you can imagine, when adopting a dog from unconventional sources, you are less likely to have full information about their background, including their age.

How to tell how old a puppy is? You can tell how many weeks old a puppy is by their teeth, with an estimation at least. For example, small baby teeth and lots of gum could indicate your puppy is under 8 weeks of age. Back teeth aren’t in place until 6 months of age.

By looking at their teeth, you can tell how old a puppy us. Those pearly whites grow in much faster stages than with human teeth as puppies mature so much faster.

There are, however, a few more signs you can look out for to paint a broader picture of your puppy’s age.

I will explain the nuances of aging in puppies and discuss when your puppy is officially all grown up!

How to tell how old a stray puppy is
This puppy is about 8 weeks old, and his teeth could indicate that.

How to tell how old a puppy is by their teeth

When we adopted our first puppy, we were surprised at how young she was because she was huge! A heavy black pup with long, wavy fur and paws that could knock you out. To look at her you would guess she was 8 months old, when she was actually only 4 months old.

This is when my vet at the time taught me the magic of teeth. Your puppy’s teeth are a window to their life experience.

Here is a breakdown of what puppy teeth can tell you.

Baby teeth emerge up to 8 weeks

If your puppy has grandpa-like gums with a few small teeth beginning to poke through, they are definitely younger than 8 weeks old. Dogs develop their first set of teeth by 8 weeks.

Front adult teeth come through up to 16 weeks

Your puppy will be well into the teething stage from 12 to 16 weeks as their sharp baby teeth fall out and are replaced by a shiny, new adult set. The front teeth come through first as they do with human children.

During this time, your dog will love you for some soft chew toys to soothe their aching gums as their teeth push through.

Also expect tiny teeth to be lying around everywhere – you’ve been warned.

Back adult teeth emerge up to 24 weeks

Once your puppy is around 6 months old, their back-adult teeth should be fully in place. It’s an uncomfortable time as back teeth are much larger and thicker than the front teeth, so make sure those chew toys are still within reach.

You’ll also need to be diligent with your training practices to ensure they aren’t destroying your favorite jumpers in lieu of chew toys.

Tartar builds up after 1 year

Your puppy’s first set of adult teeth will shine bright and white for around a year before they start to show signs of wear and tear. From around 7 months, tartar will build up around the back teeth. This is a completely natural part of the aging process.

Other ways to tell your new puppy’s age

As you can see, within the first year the teeth are one of the most failsafe ways knowing how to tell how old a puppy is. But there are a few other ways to uncover this mystery.

Here are the lesser-known ways of knowing how tell how old a stray puppy is


Puppies younger than 2 weeks old are quite blind! They haven’t fully opened their eyes yet. There is also a blueish-gray haze over their eyes since they are so undeveloped.

If they are constantly squinting and infrequently opening their eyes to the world, your puppy is under 2 weeks old. They will be incredibly clumsy and adorable during this time!

Handy Hint: Here’s more on when you can expect your puppy’s eyes to open after being born.


Likewise, with hearing, puppies don’t have fully functional hearing until they are 4 weeks old. They are almost completely deaf until they are born and then their ears begin to open slowly.

Don’t expect to teach them any recall tricks during this delicate time!


Like newborn babies, puppies are very sensitive during their first few weeks of life. They want to be protected, warm, and comforted.

They may even border on clingy and dozy between 2 to 10 weeks. After 12 weeks, puppies graduate into bolder, more confident characters, willing to explore every crevasse and terrorize every cat.

You can start behavior training from the 13 to 16-week mark should any undesirable habits start to show.

At what age is my puppy no longer a puppy?

They grow up so fast!

Puppies quite literally transform before your eyes. I remember our puppy blossoming from chunky, clumsy 16-week-old to heavy-footed adult in the blink of an eye.

Nothing makes you feel the passage of time so viscerally as watching your adopted puppy grow up!

Handy Hint: Did you know that all puppies are born with blue eyes? Here’s when you can expect their eye color to change to the permanent shade.

So how do you know when your puppy is all grown up? Well, it depends on two things; the breed and what you define as “puppyhood”.

Yes, dogs age rapidly but from an anatomical perspective, the most important factor in being deemed an “adult” is what they are growing into. For example, my Flat-Coated Retriever puppy took around 1 year to grow into her full size.

Giant dog breeds like Mastiffs can take 2 whole years to fully mature in body size. Toy dogs like Chihuahuas can take just 6 months! It is all relative.

The second factor is more difficult to determine; what truly is puppyhood? Is it just anatomical or do temperament and whimsy come into play too?

My dog was rambunctious and playful until well into her middle ages, only settling down a touch after her 5th birthday. Some dogs never grow out of that childishness. I’m sure we could argue the same for some human adults!

The conventional way of defining adulthood in dogs is when they have fully grown into their ideal size for their breed. But if you want to hold onto those puppy days a little longer, I’m sure your dog will maintain their puppy-like energy for a couple more years!

Handy Hint: You should also read this guide which explains how you tell when a dog has toothache, it will happen at some point.


Teeth are the most reliable way of estimating how old a puppy is. It’s never going to be 100% accurate though, so cannot be relied upon to provide an exact age in how many weeks old your puppy is.

My advice to you is to pick a date, stick with it, and celebrate it with them each year!

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Marc Aaron

I write about the things we've learned about owning dogs, the adventures we have, and any advice and tips we've picked up along the way.

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