How to Tell How Old a Puppy Is: Teeth Chart by Week

Shelter records are often blank, and a found puppy comes with no birth date at all. Here is how to tell how old a puppy is, starting with the most reliable clue: its teeth. Up to about 7 months, puppy teeth come in on a timetable that lets you, or your vet, estimate age within a few weeks. After that, all methods give a range.

Once you have an estimate, our dog age calculator converts it into human years and a life stage.

How can you tell a puppy’s age by its teeth?

Puppies are born without visible teeth. The Merck Veterinary Manual says most dogs grow 28 baby teeth, starting at 3 to 5 weeks, then replace them with 42 adult teeth from about 4 to 5 months. All adult teeth are usually in by 7 months.

What you see	Approximate age
No teeth	Under 3 weeks
Baby canines and outer incisors coming in	3–4 weeks
Baby front incisors and premolars coming in	4–6 weeks
Full set of small, needle-sharp baby teeth	About 6 weeks to 4 months
First adult front incisors (center, top and bottom)	About 4 months
Middle adult incisors; first adult molars	About 4½ months
Outer adult incisors	About 5 months
Adult canines and premolars	About 5–6 months
Last molars at the back	About 6–7 months
Full adult set (42), clean and white	7 months onwards

From the Merck Veterinary Manual tooth eruption table (dog column). Merck notes these are averages “subject to considerable variation”, so allow a few weeks either way.

Adult teeth are bigger, broader and less needle-like than baby teeth. During teething (about 4 to 7 months) you’ll often see both side by side, and puppies chew more. Merck adds that aging young dogs by teeth is “only somewhat accurate”, so treat the chart as a good estimate, not a birth certificate.

What other clues show a puppy’s age?

• Behavior and coordination. Very young puppies are wobbly; by 8 weeks most run and play confidently.
• Eating. A puppy eating solid food well is probably at least 6–8 weeks old.
• Body shape. Young puppies are round with big heads and paws; by 5–6 months many look leggy and “teenage”.
• Weight, only if you know the breed. Weight is a poor age clue on its own because breeds grow at very different speeds, but it’s very useful once you have an age estimate.

Worked example: a rescue puppy with new adult incisors

Your shelter puppy has shiny new adult front incisors but still has baby canines. On the chart, that puts it at about 4 months, or roughly 16 weeks. It weighs 15 lb, and the shelter thinks it’s a shepherd mix.

Adult size. In the puppy weight calculator, enter 15 lb at 16 weeks and choose the large size class (33–66 lb adults). At 16 weeks a large-breed puppy is at about 42% of adult weight, based on the Salt et al. 2017 growth curves, so the calculator predicts an adult weight of about 36 lb, with a likely range of 31–40 lb.

Human years. In the dog age calculator, 4 months comes out at about 7 human years: a young child, still in the puppy stage.

Food. The puppy food calculator uses the age and expected adult weight to set daily calories. Our post on how often to feed a puppy has a feeding chart by age.

If the age guess is off by a few weeks, the adult-weight range moves a bit, so re-run the numbers at each weigh-in. Our guide on how big your puppy will get explains the growth curves.

How can you tell how old an adult dog is?

Once all 42 adult teeth are in, age estimates get much rougher. Merck says vets can examine wear patterns on the teeth and estimate age in most large adult dogs with normal teeth and jaws, but that small and toy breeds are harder to age this way. Other clues include:

Clue	What it suggests	How reliable?
Tooth wear and tartar	More wear and tartar with age	Moderate in large dogs; poor in small breeds
Graying muzzle	Often appears in middle age	Weak: some dogs gray early
Cloudy-looking eyes	More common in older dogs	Weak on its own
Muscle tone and mobility	Stiffness, less muscle in seniors	Weak: injuries and weight matter

Reliability ratings are our summary; none of these gives an exact age.

A vet’s answer will usually be a range, such as “young adult, 2 to 4” or “probably 8 plus”. For a 40 lb dog estimated at 5, the dog age calculator gives about 37 human years. If the real age is 4 to 6, that’s 33 to 42, still a mature adult.

Does the exact age matter?

Mostly not. The 2019 AAHA life stage guidelines group dogs into puppy, young adult, mature adult, senior and end of life stages. Knowing the stage is what drives care:

• Puppies need puppy food until growth ends. Small and medium breeds reach adult size at about 10–12 months, large and giant breeds at 18–24 months (VCA). See when puppies stop growing.
• Seniors benefit from more frequent check-ups. Our post on when a dog is considered a senior explains why big dogs get there sooner.

When to call your vet

A new puppy should see a vet within the first few days anyway. Go sooner if your puppy:

• seems younger than 8 weeks and is without its mother
• isn’t eating, or has vomiting or diarrhea (especially with blood)
• is weak, very sleepy or cold to the touch
• has a baby tooth still in place next to the adult tooth after about 7 months
• has red, swollen gums or a broken tooth

Bring any paperwork, even a vague “found on” date. Combined with the teeth, it helps your vet narrow the estimate.