When does a chihuahua mix terrier stop growing?

.They stop growing at about 9 months. there are 1000's of homeless Chihuahuas killed every year because there are more chis than homes- so who would want to make more. Look up low cost and free clinics to get your dog fixed. Serena Chihuahua & Toy Breed Rescue www.crar.org
Depends on what kind of chihuahua. If you have a toy or a teacup. Then at about 8-10 months then that's kinda of what their size is gonna be from now on. But if you have a regular chi. Then at about a year. I have both, so I know.