7 Tips for Proper Car Seat Harness Fit

In Collaboration with Sonja Kolstad, CPST

When it comes to our children, we would do anything to protect them.

Unfortunately, navigating the world of car seats and vehicle safety isn’t as easy as it might seem on the surface.

Nine out of ten car seats on Canadian roads aren’t installed correctly, and even if they are, they aren’t being used correctly. How can this be? The reason is that there are so many car seats on the market and an even larger number of vehicle makes and models on the roads. It’s not as easy as picking a pretty pattern from the car seat aisle and popping it in your backseat: the car seat and the vehicle need to match.

On top of that, the needs and sizes of individual children mean that no one seat will work for every child.

But don’t despair! You can you make an immediate difference in the safety of your child in their car seat by making sure that your car seat’s harness fits your child correctly.

A properly adjusted harness will help keep the child IN their car seat during a collision, letting the car seat do its job of protecting their little bodies.

As a Child Passenger Safety Technician (CPST) since 2013, I’ve figured out the most common harness adjustment issues that parents experience.

Here are the seven things to verify when harnessing your child in their car seat:


1- Proper harness height. When your child is buckled up and ready to go, run your finger along the harness and into the car seat shell behind them to assess harness height.

All rear-facing children need the harness to be at or below their shoulders.

All forward-facing children need the harness to be at or above their shoulders.

If you’re not sure how to adjust your car seat’s harness height, consult your manual. Some seats adjust by raising or lowering the head rest, while others require you to uninstall the seat and rethread the straps.

2- Flat, untwisted harness. Some harnesses are more prone to twisting than others. Lower-priced seats often feature a continuous harness system that can easily lead to twists at both the hips and the shoulders.

Fix a twist as soon as you see it. If the harness buckle has flipped to the wrong direction, use the triangle trick to get it back in place.Sometimes a twist at the shoulders can be hiding under harness covers. If you can’t figure out how to untwist the seat’s straps, call the manufacturer for guidance. (Watch The Car Seat Lady.)

3- Correct crotch buckle placement. Some seats have multiple crotch buckle positions. If your car seat’s crotch buckle can be adjusted, when to move it varies by manufacturer. Having it in the correct location for your seat and child will help achieve proper harness fit and can help prevent forward head slump in rear-facing children.

Which slot is right? Check your manual!

Be sure to get acquainted with your car seat manual as it’ll tell you when to move the crotch buckle in relation to your child’s size.

4- Proper use (or not) of included inserts and head supports. Lots of car seats come with infant/toddler inserts. MANY of these have distinct guidelines for when they are to be removed. Some inserts are designed for newborns and are to be removed at a certain weight. Others are more flexible and can be removed depending on the child’s comfort and how they fit in their seat.

Your manual will tell you if an insert or head support must be removed at a certain weight or stage. If your manual doesn’t state a weight, age or provide other clear instructions on usage, it’s usually dependent on how the child fits the seat. When in doubt, contact the seat manufacturer and reach out to a CPST to help you.

Remember that when you remove inserts, especially those that seat the baby higher up in the seat, you may need to make adjustments to the harness height. Using inserts according to manufacturer’s instructions ensures your child’s comfort and safety.

5- Harness tightness. A key to proper harness fit is tightness. Most first-time parents don’t realize how tight baby’s harness should be.

Before you drive away, make sure your child’s harness passes the pinch test: try to pinch a loop of harness, horizontally, above the chest clip. If you can pinch the strap, the harness is too loose—tighten it up. No pinchable loop? Then the harness is sufficiently tight.

We no longer recommend sticking your fingers under a harness to assess the tightness. This method simply has too many variables to control. (Like where a parent may put fingers to determine tightness, how many fingers are being used, or even the size of a person’s fingers).

6- Chest clip location. The chest clip is designed to sit at armpit level or in line with the nipples. This will distribute any collision forces across the strong rib cage and keep the harness properly positioned over the child’s shoulders. Adjust the chest clip to the appropriate level once the harness is appropriately tightened.

7- Thin layers of clothing. Remember that we do not want to add extra bulk in the form of blankets, snow suits or bunting bags underneath the child’s harness. Instead, place blankets on top of the harness once the child is buckled, or use accessories such as car seat ponchos that do not interfere with the car seat straps. Hoodies can also interfere with a child’s position in their car seat, especially thick ones that push their neck forward. Have them wear the hood up, or skip the hood all together for the car ride!

Bottom line:

By properly adjusting the harness for your child every time they ride, you are making sure their car seat can perform as designed and protect them in the event of a crash.

Remember that proper harness fit is only part of the car seat safety equation: if you have doubts about your car seat installation, meet with a CPST near you to learn how to install and use your child’s seat correctly every time.

About Sonja Kolstad, CPST

© CODIO Photography

If you’re in Calgary or the surrounding areas, I’m here to help! Send me an email at info@ttdoulas.com or contact me via my website.

I’m passionate about helping families use their car seats properly. I can help you troubleshoot your current car seat situation, offer suggestions on what car seat to purchase next or come to your home to teach you how to use the car seats you own. I would be thrilled to help you today!

Book a Car Seat Check with Sonja

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Welcome to my Wolf Pack!

My name is Lindsay and I am a 40-year-old mama of four trying to live an eco-friendly, budget-friendly life! I am a substitute teacher and Child Passenger Safety technician in Calgary, Alberta. Join me on my adventures!

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