Using a car seat for your little one is essential to keep them safe while you embark on your next adventure. However, knowing when you’re legally required to get a new one is somewhat of a grey area for a lot of drivers.

That’s why we’ve put together a simple guide to help. Here’s everything you need to know about when you’ll need to change your child’s car seat.

Child car seat law

According to UK law, your little one must use a child car seat until they’re either 12 years old or 135cm tall, whichever comes first.

Child seats are classified in several different ways and there are currently two active safety test regulations, R44/04 and R129:

  • R44/04 – R44/04 seats are tested with a front impact at 32mph and a rear impact at 18mph, but there is no mandatory side impact test. These seats are chosen based on your child’s weight.
  • R129 – The test is the same as R44 but also includes a side-impact test at 15mph. These seats are chosen based on your child’s height.

When to replace a child car seat

Car seats are designed to keep your child safe while driving. However, they don’t last forever and will need to be replaced at certain times.

Here’s when you’ll need to replace your child car seat:

  • Height – Car seats are not designed to hold a child from birth through to the age of 12. Instead, you will need to change the seat as they get older and taller.
  • Weight – R44 regulated seats are chosen based on weight and will also need to be upgraded as your child gets older and heavier.
  • It’s expired – You may not be aware, but a car seat comes with an expiration date on the label or owner’s manual to make sure that it’s safe to use.
  • It’s damaged – If your car seat has been damaged or involved in a crash then this needs to be replaced, even if your child wasn’t in it at the time or it doesn’t appear to have any damage. Your insurance provider may issue a voucher if you have been in a crash (please check your policy) – these can be used in your local Halfords store.
  • If you’ve changed cars – Not all seats will fit into every car, but Halfords are available to help with any questions about fitting your seat into your new car and whether a replacement would be required. For in-person advice, visit your local Halfords store.

What size child seat do I need?

So, it’s time to replace your child’s car seat, but what size seat do you need? There are two size systems used and finding the correct size for each is easy.

i-Size seats

Height-based children’s car seats are commonly known as i-Size seats. These must be rear-facing until your little one is over 76cm, although it’s generally advised that you should keep your child in a rear-facing seat for as long as possible.

These seats come in three different sizes, each of which has a rough equivalent within the weight-based sizing system:

  • 0-85cm (approximately G0+) – rear-facing baby carrier or baby seat using a harness
  • 0-105cm (approximately G0/1/2) – rear-facing baby seat until your child is at least 76cm, then forward facing
  • 100-135cm (UK) 150cm (ROI) (approximately G2/3) – forward facing child seat

Weight-based seats

Weight-based seats are also common. These are available in more sizes should you wish to change your seat more often. Combination seats are also available which span over a larger weight range and are adjustable alongside your child’s growth.

  • 0kg-10kg (Group 0) – lie-flat baby carrier, rear-facing baby carrier or rear-facing baby seat using a harness
  • 0kg-13kg (Group 0+) – rear-facing baby carrier or rear-facing baby seat using a harness
  • 9kg-18kg (Group 1) – rear or forward-facing baby seat using a harness or safety shield
  • 15kg-25kg (Group 2) – rear or forward-facing child car seat with a high-backed booster or booster cushion, using a seat belt, harness or safety shield
  • 22kg-36kg (Group 3) – the same as Group 2

Types of child car seat

You’ve found the right size – great! Now it’s time to pick which type of car seat you need.

There are four types of seats commonly used in the UK:

Combination seats/multiple group seats

Combination car seats are adaptable and built to stand the test of time. You can adjust them to forward facing when you’re lawfully allowed and recline them for sleepy time.

Forward-facing (9kg-18kg)

Forward facing seats have multi-point harnesses that keep the seat secure, while elevated bases give your child a better view.

High-back booster (15kg-36kg)

A high-back booster seat is perfect for bigger children, usually aged around four. Most of these car seats have adjustable heights and widths to suit all sizes. You’ll find some come with their own harnesses and others will use your car’s seat belt to keep your little one secure.

Impact shield seats (forward facing only)

These seats have the look of a roller coaster seat, but don’t be fooled, they’re well-tested and provide strong head and neck protection. They have high levels of compatibility even in awkward cars and can be fitted with or without ISOFIX. These seats are great for different-aged children as they require little adjustment between uses. And importantly, these are harder to escape from than the traditional 5-point harness systems, making them great for children who dislike the restriction of a harness and need more upper-body freedom!

Fitting system

A final consideration before purchasing your new seat is what type of fitting system it uses – belted or ISOFIX.

Belted is when you use your car’s seat belt to secure the seat and ISOFIX is the term associated with cars that have an internationally standardised car seat fitting system, otherwise known as anchor points. Having this in place makes it much quicker and easier to install a seat into your car. For baby carriers, it is sometimes necessary to purchase an ISOFIX base which clips into your car and then the seat can be taken in and out of the base instead.

Why get your car seat from Halfords?

Whatever seat you choose, you want to know that it’s the best!

That’s why we always recommend that customers choose a reputable shop that only stocks the right car seats, like Halfords. All of the child seats stocked by Halfords have been through rigorous safety testing – so you know your child is in safe hands!

We also provide a free car seat fitting demonstration for all our customers, for that added peace of mind.

If you need any extra help finding the right car seat for your child, then check out our Car Seat Buyer’s Guide. You can find our full range of child car seats over at

With the uncertainty of the energy price cap and cost of living crisis, we know that you’ll be keen to save money as and when you can. Here at Halfords, we’re committed to driving down prices and offering you the best value possible to keep you safe, happy, and secure. We’ve pledged to never be beaten on price on 1000s of motoring essentials – read more here.