Puppy feeding and growth
When do large breed puppies reach their adult size?
Last updated 23 September 2026 · How we write and check this
Short answer
Large breeds, generally 25 to 45 kg (55 to 99 lb) as adults, typically reach their adult size somewhere between 12 and 18 months. Height often stabilizes toward the earlier end of that range, while chest depth and muscle mass can keep filling out closer to the later end.
A wider window than small breeds
Unlike the relatively tight 9 to 12 month window for small breeds, large breeds show more variation, with some finishing closer to a year and others, especially bigger boned working and guarding breeds, taking closer to eighteen months to fully mature.
Two stages within the large breed timeline
Height growth generally slows first, often by around 12 months, while the dog continues adding muscle and chest depth for several more months after that. A large breed dog that looks tall but still somewhat narrow at a year old is typically still in this second filling out stage.
Using weight trends to confirm the finish
As with other size categories, the most reliable confirmation is weight staying flat across at least two or three consecutive monthly checks, combined with the dog being at least 12 months old, before assuming a large breed puppy has reached full adult size.
Key takeaways
- Large breeds typically finish growing somewhere between 12 and 18 months.
- Height often stabilizes before chest depth and muscle mass finish developing.
- Bigger boned large breeds tend toward the later end of this range.
- Confirm growth has finished with several consecutive flat monthly weigh ins.