How do you install a car seat safely?
- Desiree Bobby
- 5 days ago
- 7 min read
You want your baby to be safe in the car, every time. But did you know that a car seat only provides effective protection if it's properly and securely fastened?
There are two ways to install a car seat: with ISOFIX or with the car seat belt.
Both systems are safe if used according to the rules and instructions. In practice, ISOFIX is less likely to go wrong because there's less chance of errors during installation. This often makes it the safer and easier choice.
In this blog post, I'll explain both methods. From what ISOFIX is exactly, to how to safely secure a seat with just a seat belt. Step by step. Let's start with the basics.
What is ISOFIX?
ISOFIX is an attachment system that ensures that the car seat is attached directly to the car body.
The installation system consists of 2 or 3 parts:
ISOFIX hooks in the car
Tilt protection (support leg or top tether)
An ISOFIX base (sometimes)
ISOFIX hooks
ISOFIX hooks are two metal mounting points that are attached to the car frame.
You will find them between the backrest and the seat of the rear seat.
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These hooks have been mandatory in all new cars sold in Europe since 2014. Older cars (especially those manufactured before 2006) often don't have them yet.
Sometimes ISOFIX is also located on the front passenger seat, but this varies from car to car.
Not sure if your car has ISOFIX? They're sometimes well-hidden. Check the manual, carefully feel between the backrest and the seat cushion, or look for a label or small logo with the word "ISOFIX."
What if your car doesn't have ISOFIX hooks?
That's not a problem with infant car seats (Group 0+). Many infant car seats can also be used without an ISOFIX base using the car's seat belt. This is safe as long as you secure the seat correctly according to the instructions. Read more here about safely securing your car seat with belts.
Toddler seats are different. They're often specifically designed for ISOFIX. Not every model can be installed with a seat belt. So, double-check that the seat you choose is compatible with your car.
That's why many parents choose an ISOFIX seat from the very beginning. If your car has ISOFIX, it's a smart move. You can often use the same base for the next stage, saving money and hassle.
Do not use universal ISOFIX adapters
You may have heard of universal ISOFIX adapters for retrofitting ISOFIX to a car. Don't use them.
They do not form a solid connection to the car frame and are therefore not safe.
If your car doesn't have ISOFIX, secure the seat with the seat belt or have a professional install an official ISOFIX retrofit, if possible. Always have this checked by your dealer or garage.
Tilt protection
In addition to the ISOFIX hooks, you always need an additional restraint system to prevent the seat from tipping forward in the event of a collision. This can be done via a support leg or a top tether.
Support leg
A support leg is an extra leg attached to the ISOFIX base or the seat itself. You unfold it and place it firmly on the car floor. This keeps the seat stable in the event of a collision.
Not all cars are suitable for a support leg. If there's a storage compartment or hatch under the floor, the floor isn't sturdy enough to properly support the leg. As a result, the support leg won't function as intended.
A car is suitable for a support leg if the floor is flat and firm, without any storage compartments or loose flaps. If in doubt, check the manual or have it checked by a specialist.
Top tether
A top tether is an extra strap attached to the top of the car seat. You attach this strap to a special anchor point in the back of the car, often behind the seatback or in the trunk.
To use a seat with a top tether attachment, you will need a tether hook.
The tether hook is a metal ring or bracket, sometimes visible, sometimes hidden. It usually has an icon of a car seat with a strap pulled back. This is the official top tether symbol.
Sometimes the point is marked with a label or it literally says "top tether".
The top tether is generally only used with forward-facing car seats.
Newborn babies are always transported rearward-facing. That's the safest way. In Europe, it's even legally required to travel rearward-facing until at least 15 months. But many experts recommend traveling rearward-facing for longer, up to 18 kg (40 lbs) or even up to 4 years, if the seat allows it.
When travelling rearward-facing (such as with babies or some toddler seats), a support leg is usually used as an additional attachment, not the top tether.
The top tether is designed to prevent a forward-facing seat from tipping forward in a crash. In rearward-facing travel, the force exerts a different force, and a support leg provides the appropriate support.
What if your car doesn't allow a support leg?
For example, through a storage compartment in the floor? Then there are two options:
Find a seat or base that uses a top tether and is suitable for babies. Note: this is less common with infant car seats, but some systems do exist. The Maxi-Cosi AxissFix i-Size, for example.
Use an alternative solution for the support leg , such as a storage compartment filler block. Some manufacturers (such as Maxi-Cosi) offer approved fillers. Note: This must be explicitly approved by both the seat and car manufacturer.
The car seat determines what is needed
Each seat or base is designed for one of two additional attachments: support leg or top tether. This is always stated in the seat manual or on the manufacturer's website. You cannot simply use these two systems interchangeably.
The car determines what is possible
Not every car has a top tether point. Not every car has a floor suitable for a support leg. Therefore, it's important to check whether your car is compatible with the system you intend to use.
ISOFIX Base
Many infant car seats use a separate ISOFIX base. This clicks onto the ISOFIX hooks. Then, click the car seat onto the base. Not every car seat requires a base; some toddler and child seats click directly onto the ISOFIX hooks.
Many parents appreciate an ISOFIX base because it simplifies daily use and reduces the risk of errors. You simply click the seat into place, and indicators show you whether it's properly secured.
Two types of ISOFIX bases
Base with support leg: the most commonly used variant for baby seats.
Base with top tether: more common in toddler seats.
Does every seat fit on every base?
This is an important point: a base and seat must fit together exactly.
Even within a single brand, there are multiple bases that aren't interchangeable. That's why it's often easiest to buy a seat and base as a set, or always check compatibility.
Does your car not have ISOFIX? No problem.
Many infant car seats (Group 0+) are also suitable for use with the car's seat belt. It's important to do this carefully and step by step. This way, you can be sure your baby is safe.
1. Place the seat backwards in the car
Babies should always be transported rear-facing . This provides better protection for their heads and necks in the event of a crash. Ideally, place the car seat in one of the outer rear seats. Only use the front passenger seat if it doesn't have an airbag or if you can safely deactivate it.
2. Follow the belt route in the manual
Each seat has a fixed route for the belt. This is usually indicated with blue arrows or slots on the seat. The lap section of the belt goes across the base of the seat, while the shoulder section often goes behind or around the seat. Follow this route precisely. Even a small error can have serious consequences in a crash.
3. Tighten the belt
Once the seat belt is properly positioned, tighten it firmly to prevent the seat from sliding or tipping. Check that the seat is securely in place by gently pushing on it. It should only move a few centimeters.
4. Pay attention to locking
In some cars, you have to manually lock the seat belt. In others, this happens automatically when you fully extend the belt. Check your car's manual for instructions.
5. Check the angle of the seat
A baby shouldn't sit too upright. Many car seats have an angle indicator—for example, a colored line or a bubble—to show if the seat is tilted correctly. Too upright? Their head can fall forward, restricting their breathing. Sometimes you can adjust the angle or use an approved wedge or recline adjuster (only if approved by the manufacturer).
6. Do not use loose accessories
Only use inserts, headrests, or seat belt covers supplied or approved by the seat manufacturer. Other accessories may reduce safety.
8. Check regularly
Seats can become loose with daily use. Check occasionally that everything is still securely fastened and that the belt routing is correct.
9. Pay attention to the shelf life of the seat
Seats have a limited lifespan. Plastic can age, especially after a collision or prolonged exposure to sunlight. So don't use an old seat if you don't know its history.
10. Have it checked (optional, but smart)
Not sure if it fits properly? Have the seat checked at a baby store. It's quick and easy and gives you peace of mind.
Life with a baby is full of unexpected moments.
They always manage to surprise you with things you had not expected at all.
That is precisely why it is good to have thought carefully about some things.
For example: how to transport your child safely. Whether you use ISOFIX or a seat belt, it's crucial that your baby is well-protected. Our blog posts on choosing a car seat and our blog posts on how your baby should sit in the seat explain exactly what to look for.
Want to be more prepared for everything that's coming your way? At The Baby School, you'll also learn about safe sleep, how to safely set up the nursery, and how to prepare your entire home for that first phase. For peace, clarity, and more time to enjoy life.
Love,
Bobby
