A baby will stay in an infant car seat until around 9 months to 10 months of age.
Between the ages of 9 months to 12 months babies are usually ready to move up to a convertible car seat although it depends on the size and weight of the baby.
As a general rule a baby will be ready to move out of the infant car seat when.
They've reached the maximum height or weight limit, which is typically 30 to 32 inches or 30 to 35 pounds.
The top of their head is less than an inch from the top of the seat when buckled in.
You should switch from an infant to a convertible car seat once your child reaches your infant seat's maximum weight or height, whichever comes first.
Most car seats are outgrown when your child's head is less than one inch from the top of the seat, but check your seat's manual to be sure.
Parents using an infant seat generally switch their kids to a larger, convertible seat anywhere between 9 months and 2 years, depending on their child's size (bigger kids will likely move on faster).
But they can opt to do so sooner as long as the convertible seat is rated safe for their child's height and weight.