When to Switch Car Seats

It’s a good time to be a kid in a car. Cars and car seats both continue to get safer, and child vehicle fatalities are down. Much of the effectiveness of a car seat rests in its specificity: A car seat needs to be the right fit and size for the kid and their developmental stage. But with so many car seats out there—and often numerous possible configurations, depending on the child’s age—it can be daunting to choose which seat to get and when to get it. Most families will use three different seats as their child grows: an infant seat, a convertible seat, and a booster seat. Here’s a rundown of the different types of seats, as well as the checklists to follow when you’re trying to determine whether your kid has outgrown their current seat and is ready for the next one.

Infant seat

A small child safely buckled into a car seat in the back seat of a car.
Photo: Michael Hession

An infant seat is the rear-facing, bucket-style car seat that most parents opt to use through the first year of their baby’s life, and sometimes up to age 2. (No matter where you live in the US, an appropriate car seat is required when you’re driving with an infant.) All dedicated infant seats are rear-facing-only, and the most common type snaps in and out of a base that typically stays installed in the car. So if you’re a two-car family, it’s likely that you can get just one seat and two bases. (Some parents may decide to forego the infant-specific seat and rely on a convertible car seat rated for newborn use; they usually come with an added infant insert cushion for extra support.)

All infant seats have a five-point harness, and they include a newborn insert to use from birth until a child is between 11 and 15 pounds. (Check the manual for exact guidelines, but generally if the baby’s shoulders don’t reach the straps without the insert, you should use the insert.) Most infant seats have more than one recline option. For newborns, you want the seat in the most reclined angle possible. Lani Harrison—a Child Passenger Safety Technician (CPST) who works with the car seat safety website Car Seats for the Littles and does frequent car seat installations—points out that when a parent reports their baby is crying constantly in the car, it’s often because the infant car seat is set at too steep an angle. (Note: Tiny preemies or babies with special needs or medical conditions may not be able to sit in a reclined position yet, and they might require different solutions than a typical car seat, such as a car bed.)

A child has outgrown their infant seat when either of the following happens:

  • 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.

The average baby will reach 30 to 32 inches sometime between 12 and 19 months, and most children outgrow the seat’s height limit before the weight limit. 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.

Within that age range of 9 months to 2 years, there is no documented safety difference between a rear-facing infant seat and a rear-facing convertible seat, as long as the child meets a given seat’s height and weight requirements. Because the seats are equally safe, some parents may choose to use an infant seat for as long as possible (to keep the click-in-and-out convenience of a seat that separates from its base, or multiple bases), instead of switching to a one-piece convertible seat that stays in one place. However, we’ve found that many caregivers move their babies to a rear-facing convertible seat well before they officially outgrow their infant seat, usually at the point when the bucket seat becomes too heavy to comfortably carry.

Convertible seat

A child sitting in a car seat in the back seat of a car, fully buckled in.
Photo: Kyle Fitzgerald

A convertible car seat (also called a toddler seat or an all-in-one seat, if it also converts to a booster seat later) is a seat with a five-point harness that’s designed to face both backward and forward in the car (this is why it’s called a convertible). Experts recommend keeping the seat in rear-facing mode for as long as possible. Many states require children under a year old to ride rear-facing, and increasingly state laws require kids to stay rear-facing up to the age of 2, though longer is better. Both the American Academy of Pediatrics (AAP) and the National Highway Traffic Safety Administration (NHTSA) [PDF] recommend that children stay rear-facing for as long as possible—that is, “until they reach the highest weight or height allowed by their car safety seat manufacturer,” according to the AAP. The British Medical Journal concluded in 2009 that a child is safer riding rear-facing until the age of 4. In Sweden, a country where children have a notably low fatality rate in car crashes, kids typically sit rear-facing until they’re 4 years old.

The rear-facing position is substantially safer for a young child. In a head-on collision, if a child is facing to the rear, the impact of the crash is absorbed primarily by the outer shell of the car seat (rather than by their head, neck, and spine). Also, children’s unique anatomy (they have heavy heads and stretchy bones) makes them more susceptible than adults to neck and spinal cord injuries in a car accident, and riding rear-facing can help protect those areas.

Some parents decide to turn a child forward-facing before they outgrow the rear-facing limits, often because they find it easier to interact with their child or hand them snacks this way, or because they think the child is less likely to get car sick or simply prefers it. Convertible seats have a minimum weight requirement set by the manufacturer for forward-facing riders, usually around 20 pounds, which is far too low (that would be the average weight of a 1-year-old). Now, age 2 is becoming the more widely accepted minimum standard, but again, experts agree that older is better.

A child has outgrown the rear-facing position in a convertible car seat when either of the following happens:

  • They reach their convertible seat’s rear-facing height and/or weight limit. (Our guide to the best convertible and all-in-one seats prioritizes seats that have generous rear-facing weight limits, which help keep kids comfy in that position longer.)
  • The gap between the top of the child’s head and the top of the car seat shell or head restraint is less than 1 inch. This measurement can be more useful than overall height limits; a short kid with a long torso may outgrow their seat sooner.

Like an infant seat, a convertible seat relies on a five-point harness to keep a kid restrained. Although the laws vary, many states require that a kid remain in a car seat with a five-point harness until they’re at least 40 pounds or 4 years old. Experts, however, recommend that you keep your child in a five-point harness until they outgrow the seat’s height and weight limits. Don’t rush moving to a booster.

A child has outgrown a forward-facing convertible seat when:

  • They hit the seat’s height or weight limit (which, for all of Wirecutter’s current picks, is 49 inches and 65 pounds).
  • The tops of their ears reach the top of the car seat’s shell or head restraint.
  • The harness straps can’t be positioned at or above their shoulders.

Booster seat

A child sitting in a car seat in the back seat of a car with a seatbelt on, smiling.
Photo: Kalee Thompson

Infant and convertible seats have their own five-point harnesses, but when a child is riding in a booster seat, the car’s safety belt is the only means of restraint. The purpose of a booster is to raise up the child, positioning them so the safety belt fits properly and falls against the firm parts of their body, like the shoulders and legs, rather than the soft parts, like the stomach.

High-back boosters (which have backs and typically both wings and a headrest) provide some additional side-impact protection to the head, neck, and upper back; backless boosters do not. In our guide to the best booster seats, we have picks for both high-back and backless boosters. But for everyday use we recommend high-back boosters (until a kid outgrows the high-back height or weight limit) because of the additional protection they provide. Many high-back boosters, including some of our picks, convert from high-back to backless.

Before you move a kid to a booster, they must meet the following guidelines:

  • A child should weigh 40 pounds (minimum) and be 38 to 40 inches tall, though this varies according to state laws and individual seat manufacturers’ recommendations.
  • They should be at least 4 years old (minimum).
  • A child should be able to understand and accept the need to sit still in the car.
  • They should be able to avoid slumping or slouching over in the car (including during naps); incorrect posture could lead to them being injured in the case of an accident.

A child should stay in a high-back booster until they reach the seat’s high-back height or weight limits, or until the tops of their ears reach the top of the head restraint, and then move to a backless booster.

The NHTSA estimates that most children are ready to make the switch from riding in a booster seat to using the vehicle’s seat belt alone at some point between the ages of 8 and 12. They’re able to ride without a booster when:

  • They are tall enough to remain in place—or at least not slide through the seat belt—if the car stops suddenly.
  • They’re able to keep their back against the vehicle seat, knees bent over the edge, and feet flat on the floor.
  • They fit in a seat belt properly, with it positioned across their collarbone, low on their hips, and touching the tops of their thighs.
  • They can maintain correct posture for the entire car ride.

Regardless of what type of safety restraint a child is in, experts recommend that they continue sitting in the back seat of the car (PDF) until they are at least 13 years old. For more details on choosing a car seat and on car seat best practices, see our guides to infant seats, convertible and all-in-one seats, and booster seats.

Additional reporting by Ingela Ratledge Amundson.

This article was edited by Ingela Ratledge Amundson and Kalee Thompson.

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