When Can a Child Use a Booster Seat?

Two little boys sitting on a car seat and a booster seat buckled up in the car. Children’s Car Seat Safety

Let’s be honest—carrying around that bulky baby car seat is a pain in the wrist, and you can’t wait for the day when your kid can fit into a booster seat that just stays in the car. But how do you know when that day has come?

A child can use a booster seat from the time they reach 40 pounds up until the booster makes them too tall for the seat. The child needs to sit in the booster seat high enough that the shoulder belt can function properly, and the back of the seat or headrest has to reach above their ears.

In addition to when your child is ready for a booster seat, we’ll look at the factors that determine which kind of booster seat they need, and when. We’ll also look at things to consider when buying a booster seat, when being in a crash demands a replacement, and how you know it’s safe to let your child graduate from the booster seat.

Combination or Convertible Seat

A combination, or convertible, seat is a forward-facing seat with a harness. It could be an all-in-one seat or a car seat that can be used as either a rear-facing or forward-facing car seat.

When your child is over 40 pounds, you can remove the harness and start using the car’s seat belt, essentially making it a high-back booster seat! If you do this, make sure the lap and shoulder belts can both fit snugly. Most seats have space under the armrests for the lap belt to go, as well as hollows beneath the headrest for the shoulder belt.

Safety Car seat for baby and kid, isolated on white background

But this is not always the case; sometimes the shape is such that the lap belt is kept too high to do anything. It might also lack hollows for the shoulder belt, suspending the belt away from your child instead of fitting snugly. 

If this is the case, the lap belt won’t be able to work properly, and you’re better off keeping the harness on. An improperly fitting seatbelt is more dangerous than no seatbelt at all.

This shouldn’t usually be a problem, but it’s important to know that it’s a possibility.

Check the specifications of your harness—some will accommodate kids up to 65 pounds, though this may not be the case for seats made before 2014. (Source)

High-Back Seat

A high-back seat is a booster seat made specifically to be used with a seat belt for a child who is 40 pounds or more. Kids typically reach 40 pounds at around age 5, but that’s just something to give you an idea of around the time you should start expecting the switch. Your child will grow at their own pace. (Source)

No need to worry about harness specifications or whether the seat belt will fit the right way because these seats are designed to give the seat belt its entire functionality. 

There’s a channel under the armrest for the lap belt, and most seats even have belt position guides that hold the shoulder belt in place so that it can do its job without causing your child too much irritation. Some even have several options for belt position, making it customizable as your child grows taller.

boy sits in a car seat

This makes the high-back booster seat great for kids who have just graduated from the harness, but who are still short enough that the shoulder belt rubs against their face, ears, or neck if it’s not held down a bit for them.

The high-backs also often provide cushioning and protection from whiplash with its headrest designed to reach well above your child’s ears and supportive padding on either side. So, if your car has low seatbacks, or your child likes to nap in the car, you might want to keep them in this seat all the way up until they’re too tall for it. (Source)

Some high-backs feature removable backs, allowing you to turn the seat from a high-back into a backless seat once your child is tall enough to use the shoulder belt without needing a belt position guide.

Backless Seat

Once your child is tall enough to not need the guides on the high-back, or if you have other ways of making the shoulder belt work without the high-back, they can graduate to the backless booster seat.

Also called a no-back seat, this seat is just what it sounds like: a seat that’s only function is to boost your child up a bit so that the shoulder belt can work. 

Backless seats are also a lot easier to install and move around than other seats, as they’re much smaller, lighter, and simpler. You don’t even have to anchor it in, as it’s just there for height. Your child sitting in it combined with the seatbelt is enough to keep it in place.

When using a backless seat, you need to start considering the height of your car’s seatbacks. They have to come up past your child’s ears in order to protect them from whiplash. (Source)

The reason for this is that the ears are at the same height as the base of the skull. So, keeping something behind there will help prevent the backward motion that initiates whiplash.

If the backs of the seats in your car are too low, either install headrests or stick with the high-back seat. It’s always better to be safe than sorry, especially when it comes to protecting your kids.

Safe movement of children in the car. An adorable boy buckles the seat belt of his car seat inside the car. Child safety transportation concepts

Buying a Booster Seat

When choosing a booster seat for your child, don’t be discouraged by the range of prices. All booster seats have to pass the same tests, so a cheaper seat is just as safe as an expensive one. 

An expensive seat might have more amenities, such as cushioning, cupholders, and a cover that you can remove and wash, but when it comes to safety, all seats made after 2014 will provide the same level of safety. So don’t feel like you’re putting your child in danger by getting a cheaper seat—it’s fine, it’ll do its job and protect them.

The same buying standards do not apply when buying used booster seats. As a general rule, you should avoid buying used car seats from garage sales and yard sales, and especially thrift stores. 

These used seats may have been in a crash, and unless you get an honest account from the previous user, there’s no way of knowing the seat’s history. You might be able to learn the seat’s history from the seller of a garage sale, but you’ll have no such luck at a thrift store, as the seat was donated there and the donator isn’t there to tell you about it.

Booster Seats in Car Crashes

The reason it’s so important to know the history of the seat is that you don’t want to seat your child in a seat that might be damaged. Some damages caused by a crash may be undetectable by the naked eye, so the person selling it may think it’s fine, and ignorantly deceive you into also thinking it’s fine. It’s not.

The NHTSA has five standards used to determine whether a seat is safe to consider using after a crash, or whether it should be replaced. If any of these standards are not met, the seat should no longer be considered safe to use, despite any appearances of still being intact:

  • Was the car able to be driven away from the crash site? If so, the seat may still be safe. If not, and the car had to be towed, the seat should be replaced.
  • Was the door closest to the seat damaged in any way? If not, the seat may be safe, but if so, the seat should be replaced.
  • Was anyone in the vehicle injured at all? If there were injuries, the seat should be replaced, but if not, it could still be safe.
  • Were any of the airbags in the car deployed? If not, the seat may still be safe to use.
  • If there any visible damage to the car seat? This isn’t the end-all-be-all of seat safety, but if you can see that the seat is damaged, you should definitely replace it.

If these five standards are met favorably, then the crash was a minor one. If that’s the case with the crash the seat was in, call the manufacturer to see if it’s still safe to use. Include details of the crash that show the severity of it. If they still suggest replacing the seat, trust their judgment and replace the seat. Better to err on the safe side. (Source)

When Does a Child Grow Out of a Booster Seat?

But what about when your child is a “big kid,” or says they’re too old for a booster seat? You might be tired of the complaints that none of their friends have booster seats, but safety comes first!

A definite sign that your child is too tall for a booster seat is when their ears come above the back of the seat. At that point, either the back needs to go up higher, or they need to start sitting lower, as there’s nothing left protecting them from whiplash. If it turns out that your child doesn’t yet fit the adult seat belt, add a headrest to their seat.

Height and age aren’t perfect meters for when they’re done with the car seat. Some people say 4’9″ tall, while others say age 8. Some say 80 lbs, and others say age 12. There’s no one benchmark, but that’s as expected: every child is different.

As such, you need to check with your child to see if they fit the seat belts in your car (if there’s more than one car they ride in, you should check both cars, as different cars have differently shaped seats).

You’ll know that the seat belt properly fits your child based on SafetyBeltSafe U.S.A.‘s 5-Step Test. 

  1. Can they sit all the way back in the seat?
  2. Do their knees bend comfortably at the edge of the seat?
  3. Does the lap belt rest snugly on their thighs (not the tummy!)?
  4. Is the shoulder belt positioned properly on the shoulder?
  5. Can they sit like that through your whole drive?

If all these conditions are met, then your child is ready for the seat belt! (Source)

Seat Belt Safety: Why You Need to Wear It Right

The whole reason for a booster seat is to make the car’s seat belt usable for your child. It’s critical for seatbelts to be properly positioned, else they cause more harm than good in a crash. 

When your child is too small to use a seat belt without a booster, the seat belt will not be properly positioned if they’re not boosted up. The shoulder belt will come up against their neck or face instead of their shoulder, and their short legs may cause them to want to sit too far forward in the seat so that their legs can bend, making the lap belt equally useless.

Seat belts are supposed to fit snugly, maintaining a slight pressure that will hold the wearer in place against the seat during a crash. This doesn’t work if the seat belt is worn loosely, if the wearer isn’t sitting against the seat, or if the belt comes across any part of the body that it shouldn’t. 

Improperly worn seat belts can be even more dangerous than no seat belt at all, as in a crash they can cause injuries to internal organs; fractures in bone structures such as the sternum, shoulder, or spinal cord; and internal bleeding. This comes as a result of the seat belt’s inability to do its job and keep its wearer in place, all because it was positioned incorrectly.

Happy kids, adorable girl with her brother sitting together in modern car locked with safety belts enjoying family vacation trip on summer weekend

A booster seat lifts up your child so that they can be at the proper height for the seat belt to be positioned properly. It makes them high enough so that the shoulder belt can come against their shoulder (the guides on high-backs do this for shorter kids), it hugs them against the seat, and its own seat is short enough that they can bend their legs without scooting forward. 

Ensure your kids can and do always wear their seat belts safely because prevention is always better than regret. 

About Shelly

Shelly Courtney has a rich knowledge about babies and parenting that she has gathered from a decade of experience interacting with relatives, friends, and colleagues. Being a doting mother herself, Shelly loves sharing her experiences on the nitty-gritty of parenthood with other budding parents. Her parenting advice is sure to make parenthood more enjoyable for all the new moms and dads.