Booster Seats vs. Car Seats With Harness Straps

Baby in car seat.
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It's important to understand the differences between a car seat and a booster seat. When a child sits in a car seat, they wear its five-point harness as their restraint. A child on a booster seat uses the vehicle's seat belt across them (like an adult does) as their restraint. Many car seats with harnesses can later be turned into a booster.

Before you move your child to a booster seat, make sure they meet three important criteria. To sit safely in a booster seat, a child should be:

  • At least 5 years old
  • At least 40 pounds
  • Able to sit in the booster without slouching, leaning over, or playing with the seat belt

There are many convertible seats and combination seats that allow you to use harness straps up until your child is 40 pounds or more (many can be used until kids are up to 65 pounds or 49 inches tall). These seats allow you to keep your child in a car seat with a harness for longer.

When to Switch to a Booster Seat

In general, the AAP states that "booster seats are for older children who have outgrown their forward-facing seats." But since they also state that children "should use a forward-facing seat with a harness for as long as possible, up to the highest weight or height allowed by their car safety seat manufacturer," they aren't encouraging an early switch to a booster seat. Instead, check the manual for your harness-style seat and use it until your child meets its weight or height limit.

If your child's shoulders reach the top strap slot on their car seat, but they don't meet all three booster minimums, then they need a different car seat that has a higher top shoulder strap height to allow them to remain in a five-point harness for longer. Most kids outgrow their five-point harness in height (when their shoulders reach the top slot) rather than weight.

The CDC recommends that children ride in a forward-facing car seat "until at least age five or when they reach the upper weight or height limit of their particular seat," after which they should be buckled into a belt-positioning booster seat in the back seat

The National Highway Traffic Safety Administration agrees, stating that parents should keep kids in forward-facing seats with a harness and tether until they reach the top height or weight limit allowed the seat’s manufacturer. The NHTSA also offers an age range of four to seven years as a good time for when kids might be ready to move to a booster seat.

There are many belt-positioning booster seats with minimum weight limits of 30 to 33 pounds, but the American Academy of Pediatrics has long recommended that children stay in a car safety seat with a harness as long as possible before transitioning to a booster seat.

Why do manufacturers and retailers sell booster seats without harness straps with weight limits below 40 pounds if you should use a harness strap below this weight? Because they can; there is no law making the minimum weight for boosters at least 40 pounds (although such legislation is being proposed).

Some kids complain about being in a car seat and want to be in a big kid booster. But they are safest in a car seat's five-point harness until they meet all of the age, height, weight, and maturity recommendations for riding in a booster. And safety is a non-negotiable.

A Word From Verywell

The bottom line is that you shouldn't be in a rush to move your child into a booster seat. To be safe, keep your child in a forward-facing car seat with a harness as long as you can, until they are at least 5 years old, at least 40 pounds, and able to sit properly in a booster for the entire ride. Always follow the manufacturer's instructions on height and weight limits, installation, and expiration.

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  1. American Academy of Pediatrics. Car Seats: Product Listing for 2021. Updated February 8, 2021.

  2. Durbin DR, Hoffman BD, Council on Injury, Violence, and Poison Prevention. Child passenger safety. Pediatrics. 2018;142(5):e20182460. doi:10.1542/peds.2018-2460

  3. Centers for Disease Control. Child passenger safety. Updated September 25, 2019.

  4. U.S. Department of Transportation National Highway Traffic Safety Administration. Car seats and booster seats.