Which car seat stage fits your child now, from age, weight, height and your seat’s labeled limits
Updated October 2026
The American Academy of Pediatrics’ policy statement sets four stages: rear-facing as long as possible; forward-facing with a harness from the time a child outgrows rear-facing, for most children through at least age 4; a belt-positioning booster from the time the harness is outgrown, for most through at least age 8; and lap and shoulder belts after that. Each move to the next stage gives somewhat less protection, so the AAP advises delaying every transition as long as the seat allows. NHTSA’s age guide says the same: under age 1 always rear-facing, rear-facing as long as possible through age 3, a harness and tether to the seat’s limit, and a booster until the belt fits.
The calculator follows the AAP sequence and your seat’s labeled limits. Under age 1, the answer is always rear-facing. Otherwise, a child below the seat’s rear-facing weight and height limits stays rear-facing; above them but within the harness limits, forward-facing with a harness and top tether; past the harness limits, a booster, until the child is at least 4 ft 9 in (57 in), at least 8 years old (the AAP’s booster age for most children) and the belt passes the fit check. Example: a 6-year-old at 48 in and 50 lb in a seat whose harness ends at 47 in has outgrown the harness by height, so the answer is a booster, 9 in short of the typical belt-fit height.
| Child and seat | Stage |
|---|---|
| Infant, 11 months, 22 lb, 29 in (rear-facing limit 40 lb) | Rear-facing |
| 3-year-old, 38 lb, 38 in, seat rear-faces to 40 lb | Rear-facing |
| 3-year-old, 38 lb, seat rear-faces only to 35 lb | Forward-facing with harness |
| 6-year-old, 50 lb, 48 in, harness height limit 47 in | Booster |
| 10-year-old, 70 lb, 4 ft 7 in | Booster |
| 11-year-old, 85 lb, 4 ft 10 in, belt fits | Seat belt, back seat |
| 11-year-old, 4 ft 10 in, fit check not done | Booster |
Limits are printed on the seat and in its manual, and they vary by model. HealthyChildren.org gives typical ranges: rear-facing-only infant seats to 22–35 lb and 26–35 in; convertible and all-in-one seats rear-facing to as much as 40–50 lb, which lets most children ride rear-facing for 2 years or more; combination seats with a harness to 40–65 lb, and as boosters to 100–120 lb. A child has also outgrown a forward-facing harness when the shoulders are above the top harness slots or the tops of the ears reach the top of the seat. Enter your own seat’s numbers; the defaults are placeholders.
An adult belt fits when the shoulder belt crosses the middle of the chest and shoulder, not the neck; the lap belt lies low and snug across the upper thighs, not the belly; and the child can sit with the back against the seat and knees bent over its edge, without slouching, for the whole trip. Most children do not fit an adult belt without a booster until 10 to 12 years. Boosters need a lap and shoulder belt; never use one with a lap-only belt.
The AAP and HealthyChildren.org say all children younger than 13 should ride in the back seat; NHTSA says at least through age 12. Never place a rear-facing seat in front of an active passenger airbag: a deploying airbag strikes the back of the seat near the child’s head.
A certified child passenger safety technician (CPST) can check the installation and the harness fit, and help choose the best seating position in your vehicle. NHTSA notes that certified technicians inspect car seats free of charge in most cases, and some offer virtual checks; NHTSA’s site lists inspection stations and state contacts. Talk to your pediatrician about children with special health care needs, preterm infants, or a child who does not fit the usual ranges.
Every state has a child restraint law, and the age, weight and height minimums differ from state to state and change over time. The recommendations here are safety guidance and often go beyond the legal minimum; check your own state’s current law for the requirement.
It does not check a specific seat model, its expiration date or crash history, or your vehicle’s anchors and belts. It does not give legal requirements for any state or country. Always follow the seat’s manual and your vehicle owner’s manual.
Turning forward on a birthday. The switch should come at the seat’s rear-facing limit, not at age 1 or 2.
Moving to a booster early. A harness protects better until the child outgrows it, at least to age 4.
Dropping the booster by age alone. Use height and the fit check.
A loose harness or a tucked shoulder belt. Both remove protection; the shoulder belt never goes under the arm or behind the back.