The four car seat stages
| Stage | Typical limits (AAP) | Move on when |
|---|---|---|
| 1. Rear-facing seat | Infant seats 22 to 35 lb and 26 to 35 in; convertible and all-in-one seats 40 to 50 lb rear-facing | They pass the seat's rear-facing weight or height limit (never before age 1) |
| 2. Forward-facing seat with a harness | 40 to 65 lb, depending on the model | They pass the harness weight or height limit (at least age 4) |
| 3. Belt-positioning booster | Many go to 100 to 120 lb | The seat belt fits: typically 4 ft 9 in, between 8 and 12 years (at least age 8) |
| 4. Seat belt | Lap and shoulder belt | In the back seat until 13 |
Why it goes by size, not age
Each step down the list protects a child a little less, so the guidance from the American Academy of Pediatrics (AAP) and the National Highway Traffic Safety Administration (NHTSA) is to stay in each stage as long as the seat allows and move on only when your child outgrows it. In 2018 the AAP dropped its "rear-facing until 2" milestone for the same reason. Two children of the same age can be years apart in when they outgrow a seat, which is why the calculator asks for weight and height, and why the limits on your own seat's label have the final say.
The ages in the guidance are floors, not targets: rear-facing always under 1, a harness through at least age 4, and a booster through at least age 8.
NHTSA's recommendations by age
| Age | Recommendation |
|---|---|
| Birth to 12 months | Always rear-facing. Convertible and all-in-one seats usually have higher rear-facing limits than infant-only seats, so children can stay rear-facing longer. |
| 1 to 3 years | Rear-facing as long as possible, until the seat's top rear-facing height or weight limit; then forward-facing with a harness and tether. |
| 4 to 7 years | Forward-facing with a harness and tether until the seat's top height or weight limit; then a booster seat, still in the back seat. |
| 8 to 12 years | A booster seat until the seat belt fits properly; still in the back seat. |
Rear-facing as long as possible
NHTSA calls keeping a child rear-facing as long as possible "the best way to keep him or her safe". An infant-only seat usually has lower limits than a convertible seat; when a baby outgrows one before their first birthday, the next seat is a convertible seat installed rear-facing, not a forward-facing seat.
A rear-facing child faces the back window, so you can't see them from the front. That is what a baby car mirror is for: mounted on the headrest in front of the car seat, it shows your child's face in your rearview mirror.
When the seat belt fits
A booster lifts your child so the adult belt sits where it should. The AAP's belt-fit checks, often run as a five-step test with your child in the back seat without the booster:
- Sits all the way back against the vehicle seat.
- Knees bend over the edge of the seat without slouching.
- The lap belt is low and snug across the upper thighs, not the belly.
- The shoulder belt crosses the middle of the chest and shoulder, not the neck or throat.
- Can stay comfortably in this position for the whole trip.
If any check fails, keep using the booster. Most children pass between 10 and 12, once they are about 4 ft 9 in tall. Check again in every car, since seats and belts differ.