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What is ISOFIX and how does it work?

June 09, 2023 by

Want to know what the ISOFIX child car seat system is and how it works? You’ve come to the right place

If you’re in the market for a new car and you have or are about to have a child or children, you’ve probably come across the term ISOFIX in relation to child car seats. But what is ISOFIX, how does it work, and is it worth having? This guide will answer all this, and more.

How does ISOFIX work?

Before ISOFIX came along the standard method for securing child seats in a car was to use the vehicle’s seatbelt. This can be fiddly, though, and also poses the risk that the seatbelt won’t be attached to the child seat properly, posing risks in the event of a collision.

ISOFIX, which is named after the International Organization for Standardization, or ISO, is a standardised system for securely attaching child seats into cars.

In broad terms, an ISOFIX child seat will have two metal or plastic arms that extend from the seat and securely lock into dedicated anchor points in the car – typically in the gap between the backrest and the seat squab of the rear seats. The seat will then stay anchored in place, and can only be removed by pressing release buttons on the ISOFIX arms that unlatch the attachment. Some two-seater sports cars offer ISOFIX in the passenger seat, though this may be an optional extra, so do research this.

Baby seats must have a third point of security, too: either a leg that extends from the base of the child seat to the floor of the car, or a ‘top tether/anchor’ comprising a strap that extends over the backrest of the rear seat, and onto a securing point on its other side, in the boot.

Is ISOFIX safer than a seatbelt?

Yes, ISOFIX is safer than using a seatbelt for two main reasons: first, as discussed above, there remains the potential for a seatbelt to not be properly looped around the securing points on a child seat. ISOFIX massively reduces the risk of an improperly installed child seat, as the arms that lock into the anchor hooks give a veritable ‘click’ when secured, while a green indicator will also often show on the ISOFIX seat when it is securely attached.

Second, there is no slack in a seatbelt securing the seat to the car to be overcome in the even of a collision, improving safety further by reducing seat movement.

Does my car have ISOFIX?

Almost certainly: it has been a legal requirement to fit ISOFIX points in all cars with four or more seats sold from new since 2014, while all brand-new model launched to the market had to have ISOFIX by 2012. Many car makers were fitting ISOFIX points well ahead of these dates, though.

If you’re looking at second-hand cars ISOFIX should be listed in the vehicle’s specifications, or you can look out either for the two anchor points in photos of the car, or the ISOFIX logo, which is a stylised image of a child in a car seat.

The ISOFIX system is called LATCH, Canfix, LUAS or UCSSS in markets outside Europe.

Types of ISOFIX car seats

A key point of ISOFIX is that it is a near-universal system, with a standard securing mechanism and two anchor arms placed at the same points in almost all cars.

There is a caveat to this, though, in that while most ISOFIX seats are universal and should work in all cars, some are semi-universal so may not fit in all vehicles, while a small number are vehicle-specific, so are designed only for one particular model of car; these differences should be clearly labelled at point of sale, though.

Do note that while the ISOFIX system is near-universal, how you access the anchor points in a car can vary. The points, which are essentially U-shaped metal bars mounted to fixed points in the rear seats, may be easily visible, could be hidden behind a removable panel or covers in the seat, or could be buried between the seat squab and backrest.

Do also note that not all cars with ISOFIX have a top tether point, either, so do your research before choosing a seat with this arrangement.

It’s also worth highlighting that just because a car has ISOFIX points, this doesn’t mean every seat will fit in the car. If you have a sports car with tiny rear seats, you may not be able to fit a baby seat with a support leg back there and have enough legroom for a front passenger, for example.

Most family cars have two ISOFIX points in the rear seats, but a small number of cars have three ISOFIX points, although the third set of anchor points can be in the front passenger seat, rather than the three sets of points being spread across the rear seats.

What’s the difference between ISOFIX and ISOFIT?

Just to make things slightly more confusing, there’s also a system called ISOFIT (emphasis ours). The anchor points on an ISOFIT seat are identical to those on an ISOFIX one, but while an ISOFIX seat will have its own five-point built-in seatbelt that secures the child to the child seat, an ISOFIT seat secures to the car using the same points, but sees the car’s seatbelt secure the child to the car seat. ISOFIT seats tend to be for older children – for example a high-back booster seat is more likely to use the ISOFIT system.

How to fit and remove an ISOFIX car seat

While the process for fitting and removing an ISOFIX seat varies slightly from car to car and seat to seat, and instructions both for the car and the child seat should be closely consulted, in broad terms the steps for fitting an ISOFIX seat are as follows:

  1. Locate the ISOFIX anchor points in the car; this may require removing a cover, or sticking your hand down between the seat backrest and squab.
  2. Extend the ISOFIX arms from the child seat, and ready the support leg or top-tether strap, if applicable.
  3. Insert the anchor arms so they attach securely to the anchor points. You should hear and feel a positive ‘click’, and a green light or icon may show on the child seat.
  4. ISOFIX bars tend to extend out quite far to allow them to fit cars with longer seat squabs. Retract the ISOFIX bars back into the seat base until the back of child seat meets the car’s backrest.
  5. Secure the top tether or support leg, if the seat has one.
  6. Put any ISOFIX cover in a safe place for future use

Some ISOFIX seats come with inserts that slot between the car’s seat-back and squab; this can be useful if the car’s ISOFIX anchor points are buried between the base and back of the seats, as the inserts will effectively open a gap through which the ISOFIX arms can slide, saving you from having to wiggle the arms through a tight gap every time you fit or remove a seat.

The yellow loops are the car’s ISOFIX anchor points; the purple arms are the child-seat latches; the blue insert is not found on all seats, but is a guide to ease fitting and refitting

The process for removing an ISOFIX seat is as follows:

  1. Loosen and detach the top tether, or take the tension out of the support leg, is using.
  2. Activate the release buttons on both anchor arms simultaneously; this can be fiddly, but gets easier as you become familiar with the seat.
  3. Remove the seat from the car, and replace any covers the vehicle’s ISOFIX points have.

What ages are ISOFIX car seats suitable for?

ISOFIX is a securing mechanism, rather than being a type of seat, so ISOFIX seats are available for children until they’re old enough to use just an adult seatbelt; this, by law, is once they turn 12 years old or grow to 135cm in height. Our in-depth guide to child-seat laws has more information, but in broad terms there are five seat groups:

  • Group 0 covers lie-flat baby carriers for infants weighing up to 10kg
  • Group 0+ comprises rear-facing baby carriers for infants weighing up to 13kg
  • Group 1 covers rear or forward-facing seats for children weighing 9-18kg
  • Group 2 covers rear or forward-facing seats, and high-backed booster seats, for children weighing 15-25kg
  • Group 3 covers rear or forward-facing seats, and high-backed booster seats, for children weighing 22-36kg

Concurrently, there is a system called ‘i-Size’, which sees seats grouped according to a child’s height. All i-Size seats come with ISOFIX points.