Switch to a convertible seat once your baby has grown out of an infant seat.
Infant seats have height and weight guidelines, but most babies max out on the height of the seat first. While some reports say to switch your baby to a convertible seat as soon as they reach their first birthday, Hawker says to pay attention to the space between the child's head and the shell of the seat. If there is less than an inch of space between the two, they're too tall and it's time to upgrade them to a convertible seat that can accommodate their height. If your child is older than 12 months and hasn't grown out on her infant seat, it's OK to keep using it, but Hawker also says, "A rear-facing convertible car seat is an excellent option for children just over 1 year old," whether they've maxed out on their infant seat or not.