Harness or Booster: When to Make the Switch!

It’s a question that comes up with invariable regularity for a CPST: when should my child make the switch from a 5 point harness to a belt positioning booster? Since each child and each situation is different, we’re not armed with one set answer; instead there are there are a few things to consider in making this move.

First, let’s define harnessed car seat versus booster seat:

Left: Britax Frontier 85 five point harness. Right: RECARO Vivo belt positioning booster

Left: Britax Frontier 85 five point harness. Right: RECARO Vivo belt positioning booster

A 5 point harness has, you guessed it!, 5 points of contact: shoulder, shoulder, hip, hip, crotch. A belt positioning booster is simply a positioning device designed to position the adult-sized seat belt over a child’s body. The major difference is that a 5 point harness is a restraint. When a harnessed seat is properly tightened, it doesn’t allow the child freedom to move out of position. A belt positioning booster, in contrast, is a seat belt positioning device. Seat belts are designed to fit fully grown adults, children need a booster to correctly position the seat belt over their small body.

Moving a child to a booster seat gives them freedom that they’ve never had before: freedom to lean sideways, slouch, bother their sister, pick up a toy off the floor, and so on and so forth. If a child is wiggling out of position at the time of a crash, that leaves them vulnerable to serious injury.

That means the decision to move from harness to booster is rooted in the child’s maturity. The ability to sit correctly for the entire ride, 100% of the time, happens somewhere past age 5 for most kids, and not until 6 or 7 for a many others.


Booster training in the Graco TurboBooster with Safety Surround

Booster training in the Graco TurboBooster with Safety Surround

My son is 5 1/2 years old, and we’ve been practicing riding in a booster for short trips to begin introducing him to the responsibility (an endeavor many technicians refer to as “booster training”).

Let me tell you how this goes. For the first few minutes, maybe even a few weeks; things are going great. You think, gosh, my kid is so mature! He’s following all the rules, he’s sitting up straight, we’ve got this booster thing locked down!

And then, something shiny detracts their focus. The inner toddler comes out, and all the sudden you’ve got this happening in your backseat:

What happens when immature kids try and ride in boosters!

What happens when immature kids try to ride in boosters!

And that is when you’ll know that your child just isn’t quite there yet. Or, maybe your child is nothing like mine and they simply nod in agreement to The Rules of Booster Seats and you never have to mention them again. The right time to switch is different for every child: however, there is not a three-year old on the planet who is ready for the responsibility, despite the 3 year age minimum on many boosters. For the average child the maturity sinks in somewhere between 5 and 7.  There are a lot of 8 year olds who still need reminders, too.

What about Height and Weight?

Most booster seats have a lower threshold of 30 lbs. Many don’t start until 40 lbs, so it’s important to check the requirements for the seat. For our Canadian neighbors, all booster seats have a 40 lb minimum. There is some concern that a smaller child may be able to submarine (slide forward in the seat and slip out of the seatbelt) beneath the lap belt in a crash, however, currently available studies do not have conclusive information for this phenomenon. We do know that a properly fitted seat belt does an excellent job of protecting a child in a crash, reducing the risk for serious injury by 45% for 4-8 year olds.1

The great news is that for most kids, there is no rush whatsoever to move into a booster seat. Not too long ago there were very few 5 point harnessed seats that could hold a child who weighs over 40 lbs. Today, there is a vast array of seats to choose from that can harness the average 5-6 year old – many of those options cost as little as $100. Check out our recommended seats list if you need help making a seat selection!

Is a Harness Safer than a Booster?

7 year old in a Graco Argos in high back booster mode

7 year old in a Graco Argos in high back booster mode

There is not any scientific information that gives us reason to believe that a harness is safer than a properly used booster seat. The key is the booster being properly used: where the child is of appropriate age and the belt is positioned properly.

NHTSA recommends utilizing a 5 point harness until the child outgrows it. There’s no rush to move to a booster right away, but if your child is nearing the weight or height maximum of their seat and is behaviorally ready to ride in a booster; don’t feel that you are reducing their safety by moving to a booster.


High Back or Backless Booster?

9 year old in an Evenflo RightFit in backless mode

9 year old in an Evenflo RightFit in backless mode

CPSTs prefer that children start out in a high back booster simply because the structure of the high back helps remind them to sit correctly. High-backed boosters also usually do a better job positioning the seat belt on smaller children than their backless counterparts. If your child likes to sleep in the car, a high back is often easier for a child to sleep comfortably without slumping out of position. When your child does move to a backless booster, be sure that they have a vehicle head restraint behind their head, at least up to the tips of their ears.

Five Step Test

Generally, kids will need a booster until they are 4’9″ tall, which happens around age 11 in many cases. To ride without a booster, a child needs to be able to pass the 5 Step Test:

  1. Sits all the way back against the vehicle seat.
  2. Knees bent at the edge of the vehicle seat and feet on the floor.
  3. Shoulder belt fits evenly across the collarbone and sits flush with the torso.
  4. Lap belt is low on the hips, touching the tops of the thighs.
  5. Can stay comfortably seated this way the entire ride.

The Bottom Line

Before moving to a booster seat, your child should be:

  • At least 5 years old.
  • Meet the weight and height minimums for the booster seat you’re considering.
  • Responsible enough to sit properly 100% of the time, even while asleep.
  • Finally, they need to have a safe belt fit. Here’s how they should look:
Proper booster fit in a RECARO Performance BOOSTER

Proper booster fit in a RECARO Performance BOOSTER


  1. Arbogast KB, Jermakian JS, Kallan MJ, Durbin DR. Effectiveness of belt positioning booster seats:  an updated assessment. Pediatrics 2009; 124; 1281-6.


Originally written by Emma Douglas. Edits maintained by CSFTL.