Seat Belt Extenders: NEVER for Car Seats or Boosters or Non-Obese Adults

What is a Seat Belt Extender?​

A seat belt extender is an extra piece that goes between the male and female ends of the seat belt to make the seat belt longer.

Extenders were initially designed for obese adults to allow them to buckle up in situations where the belt was otherwise too short to go around their body.

Now, extenders are often advertised to “solve” lots of problems – ranging from making it easier to buckle a child in a booster, or to make the seat belt fit differently on a pregnant woman.

When is it SAFE to use a Seat Belt Extender?​

The only time it is safe to use a seat belt extender in a car is when both of the following criteria are met:

  1. The person using the extender is an obese teenager or adult whose body size is such that the seat belt can not be buckled without the use of an extender. AND
  2. The extender is obtained directly from the vehicle manufacturer (not from Amazon, eBay, Walmart, AliExpress or other stores/websites).
Nissan Seat Belt extender
Seat Belt extender excerpt from Nissan owner's manual

Some vehicle manufacturers do NOT offer seat belt extenders. It is unclear why – but they may have concerns about the ability of their safety restraints to hold someone of this size in a crash. Seat belts are tested to 6,000 lbs of force – but a person weighing several hundred pounds could exert more force than this on a seat belt during a severe crash.

When is it DANGEROUS to use a Seat Belt Extender?​

  • With any car seat
  • With any booster seat
  • With any child
  • With any adult whose body size allows for the seat belt to be buckled without the need for an extender
  • With any pregnant woman (unless her body size otherwise does not allow the buckling of the seat belt)
  • To help someone buckle up when a car seat or booster is blocking someone’s access to their seat belt buckle (a different car seat or booster needs to be used, or the person needs to ride in a different spot in the car)
  • To help an adult who has difficulty buckling up – for example someone with arthritis or mobility issues

What makes seat belt extenders DANGEROUS?​

Extenders can fail in a crash - leaving the person completely unbuckled.​

Extenders are not generic. The extender must match the buckle used in that specific vehicle.

Just because you can get the seat belt to click into the extender does NOT mean the seat belt will stay buckled in a crash when several thousand pounds of force are applied to the buckle. And if the seat belt unbuckles in the crash, then not only are you in grave danger, so is everyone else in the car as you can fly on top of them.

In a crash everything becomes much heavier due to the G-forces (force of gravity). You’ll effectively weigh your usual weight times however many G’s are in the crash. In a 30mph crash like they use to crash test car seats, there are about 25 G’s. A 250 pound adult in a crash with 25 G’s is going to feel like they weigh 6,250 (250 x 25 = 6,250). Their body will put 6,250 pounds of force on the seat belt and the extender.

If you get a seatbelt extender from a specific vehicle manufacturer – let’s say Ford, for example – you can not assume it will work in all Ford vehicles. The Ford Taurus may use a different seat belt buckle than the Ford Explorer – and therefore the extender would be different for these two Ford vehicles.

Extenders can change the geometry of the seat belt on the body.

Extenders make the buckle stalk (the female end of the buckle) longer… sometimes a lot longer. As the female end gets longer it moves the buckle from the side of your hip (where it should be) farther and farther towards the middle of your body. As the buckle moves closer to the center of your body, the shoulder belt moves farther out of position, sliding onto your arm instead of resting on your collar bone. The shoulder belt has a very important job in a crash – it has to keep your head and chest held tight so that they don’t move too far forward which can cause your head to hit hard parts of the car. If the shoulder belt is on your arm – where it should never be – then your head, neck, and torso will not be well protected as the shoulder belt won’t be able to hold you back. You’ll jack-knife over yourself, making it likely that you will hit your head on something hard – like the back of the front seat, the doorframe, or the window.

With a large adult – one who otherwise couldn’t buckle their seat belt without using an extender – the use of an extender that is as short as possible to just allow them to buckle the seat belt will not change the shoulder belt fit significantly as the seat belt buckle will remain close to the side of the body rather than in front and towards the center of the body.

The smaller the person using a seat belt extender, the less it will take for the shoulder belt to slide off the arm – and the greater the risk to using a belt extender.

What if a car seat or booster is making it hard to get a seat belt buckled?​

Choose car seats and boosters that have a narrower footprint​

Click here to check out our our page on narrowest boosters.

The Maxi Cosi Rodifix booster is the best high back booster to try as not only does it have a narrow footprint but also its lack of arm rests make it easier to see and get your hand in to reach the seat belt buckle.

For a backless booster, the Graco Rightguide is the best one to try.

Climb Into a Buckled Booster

Sometimes, no matter how narrow the booster, it is too hard to get a hand in to buckle or unbuckle the seat belt each time. Try having the child climb into a buckled booster as shown in this video.

Pool Noodle Trick

If the seat belt buckle in your car is flexible, and keeps flopping down which can make it hard for some kids to buckle, try our “pool noodle trick”.

When buying a new car, look for a vehicle with flexible buckles, not rigid ones.

Flexible buckles are connected to the vehicle using a piece of seat belt material. Flexible buckles can move a little – especially side to side – which often lets them get out of the way to allow easier buckling for the person sitting next to a car seat or booster.

Rigid buckles are either connected to the vehicle using a rigid metal stalk – or they are flush with the vehicle’s seat cushion. Either way, rigid buckles can’t move out of the way even if you beg them to!

Have someone pull the buckle out of the way while you install the car seat.

For flexible buckles, sometimes you need to buckle them and have someone pull the seat belt as tight as they can to move the buckle as far away from the seat next to it… so that when you install a car seat in the neighboring position the car seat doesn’t sit on top of the buckle for another spot in the car.

Here’s an example of pulling the seat belt buckle out of the way so that it doesn’t get stuck underneath a car seat in the neighboring seat.

Shoulder strap cover trick

Try what we show in the video below if your seat belt buckle is mostly rigid (but has a little bit of give) like this one. Any soft material will do – washcloth, folded paper, etc.

Keep a child harnessed longer

It is easier to buckle and unbuckle a child in a 5 point harness than in a booster. When space is tight – or it is hard to access the seat belt buckle because it is flush with the vehicle seat – keeping a child in a 5-point harness may be a good solution.

We recommend trying the Chicco MyFit – it is relatively narrow on the outside but has a higher harness capacity (by virtue of a really high top shoulder strap height) than almost any other seat.

If the child wants to be more independent in their own unbuckling, check out the UnBuckleMe

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FTC Disclosure: Affiliate links are included in this page. No monetary compensation was provided, however, a few of the reviewed products were supplied by the manufacturer or distributor to help facilitate the review. All opinions are those of The Car Seat Lady, LLC.