A Chihuahua is full grown at about 9 months old. Most reach their adult height by 6 to 8 months and finish filling out in weight by their first birthday, per the American Kennel Club’s puppy growth guidance. As the smallest dog breed, the Chihuahua matures faster than almost any other.
Key facts
- Full grown at about 9 months; adult height typically arrives by 6 to 8 months
- The AKC breed standard sets adult weight at no more than 6 pounds; height runs about 5 to 8 inches at the shoulder
- Small breeds reach 100 percent of adult size by 12 months at the latest, per the AKC
- A female Chihuahua can have her first heat as early as 5 months, per VCA Hospitals, often before she looks fully grown
The Chihuahua growth chart
A Chihuahua puts on most of its weight in the first six months, then slows to a crawl. The weights below are typical for a dog that finishes near the breed standard ceiling of 6 pounds; lighter and heavier puppies grow on the same curve. Adult weight and the 6-pound cap come from the AKC breed standard, and the maturity timeline from the AKC’s growth guidance. Month-by-month weights are approximate, since individual puppies vary.
| Age | Stage | Typical weight | Typical height | What’s happening |
|---|---|---|---|---|
| 8 weeks | Young puppy | about 1 to 1.5 lb | about 3 in | Fast early growth; just home from the breeder |
| 3 months | Puppy | about 2 to 3 lb | about 4 in | Steepest growth stretch; gaining weight weekly |
| 6 months | Late puppy | about 3 to 4 lb | about 5 to 6 in | Near full height; first heat possible in females |
| 9 months | Near adult | about 4 to 6 lb | about 5 to 8 in | Full grown for most; height is done |
| 12 months | Adult | about 4 to 6 lb | about 5 to 8 in | Filled out; at adult weight |
When does a Chihuahua stop growing?
Height finishes before weight does. A Chihuahua reaches close to its full adult height by 6 to 8 months, then spends the next few months filling out the chest and frame, according to the AKC. By 12 months the dog is at its adult weight and the growth plates have closed.
This is the small-breed pattern: the smaller the dog, the faster it finishes. The AKC counts any dog under 20 pounds as a small breed, and those dogs reach 100 percent of adult size by a year, while a giant breed can still be growing at two. The Chihuahua sits at the extreme small end, so it crosses the finish line first. You can see the breed’s full size, weight, and care profile on the Chihuahua breed page.
Common questions
At what age is a Chihuahua fully grown? About 9 months. Adult height arrives by 6 to 8 months, and the dog reaches its final adult weight by around 12 months, per the AKC. After that a Chihuahua is fully mature.
Do female Chihuahuas stop growing earlier than males? There is no meaningful difference in when the two finish growing. Both sexes reach adult size on the same small-breed timeline of roughly 6 to 12 months. Females do reach reproductive maturity early, which can make a still-growing puppy seem more grown than she is.
At what age do Chihuahuas go into heat? Early. The average dog has her first heat at about 6 months, but small breeds can start as young as 5 months, per VCA Hospitals. A Chihuahua can come into season before she is physically full grown, so talk to your vet about timing a spay.
A Chihuahua packs an entire puppyhood into less than a year, which is part of why this tiny breed goes on to live so long. See your dog’s real age with the calculator, which uses the small-breed curve to give you a number that is actually true for your Chihuahua.
