A cat is usually fully grown at about 1 year old , though many cats keep filling out until 12–18 months. Larger breeds, and some male cats, may keep growing a bit longer.

Quick answer

  • Most cats: fully grown around 12 months.
  • Some males: may keep growing until 18 months.
  • Large breeds: can take up to 2 years or more to reach full size.

What to expect

A kitten’s body may look adult-like by the end of the first year, but muscle, weight, and overall maturity can continue developing after that.

Easy rule of thumb

If you want a simple estimate:
1 year = mostly grown ,
18 months = fully grown for many cats ,
2 years = fully grown for larger breeds.

If you want, I can also give you a month-by-month cat growth timeline.