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Car seat guide: Compatibility, laws and 123 stage

Shopping for a child car seat can be a headache. You need one that meets child car seat laws, but there are so many options to choose from.

You might hear the term ‘car seat compatibility’ a lot, which basically means finding a car seat that will fit in your car. But with new models coming out each year, it might feel that there's no end to the confusion. We’re here to help you.

A woman picks out the right car seat for her 

You have 2 options when buying a new car seat:

  • Buying a combination car seat
  • Buying a new car seat for each stage your child reaches

The benefit with combination seats is that you don’t have to change car seats as often.

But they’re usually more expensive and have fewer features than a car seat designed for one specific group.

How do I check car seat compatibility with my vehicle?

Before you buy a car seat, you need to make sure it fits in your car.

Most new cars will have Isofix fittings, so any Isofix car seat will fit.

Just bear in mind that in sportier cars this might involve moving the passenger seat forward a bit.

What are the child seat car laws in the UK?

The NHS recommends buying a suitable car seat as soon as your child is born. Hospital staff might insist that you have the car seat ready to take your child home, even if you plan on taking public transport.

Your child needs a car seat if your child is both:

  • Under 12 years old
  • Less than 135cm (4ft 5in) tall

Once they’re taller than 135cm or turn 12, they don't need a car seat but they must wear a seat belt.

There isn’t a specific booster seat age. But when your child is in what’s called ‘group stage 2’ or they weigh between 15kg and 25kg, they could use a booster instead of a car seat.

There are a few circumstances where a car seat isn’t required. For children aged under 3, the law states they don’t need a car seat in the following situations:

  • In a taxi or minicab
  • In a minibus, coach, or van
  • If there’s no room for another car seat
  • If the journey is an emergency

To view the full list of exemptions, have a look at the government’s rules.

But in most cases, child car seats are mandatory. If you fail to follow the rules, you face being handed a stiff penalty if you’re caught.

Having a properly fitted child car seat might also help reduce any worries or nervousness you might have, and might help you drive more safely.

If you're pregnant and you're unsure of how to place your seatbelt, read our safety tips for driving while pregnant.

What does car seat stage 123 mean?

Car seats are specifically designed for your baby or child’s weight and height. From when babies are 9kg, or around 76cm, right up until they reach 12 years you choose what are called ‘group 123 seats’. They’re also known as combination seats.

Can I get a combination car seat?

A 123 car seat, or a combination car seat, is the most common type of car seat in the UK. Car seats are grouped into categories – 0, 0+, 1, 2 and 3.

This table shows what weight ranges are appropriate for each group:

Group Weight range
0 - 10 kg
0 - 13 kg
0+ & 1
0 - 18 kg
9 - 18 kg
1, 2
9 - 25 kg
15 - 25 kg
1, 2, 3
9 - 36 kg
2, 3
15 - 36 kg
22 - 36 kg

What are the different types of child car seats?

Seatbelt-fitted child car seats

You need to make sure the seatbelt goes through the right guides on the child seat.

If it’s a backwards-facing seat, pass the seatbelt through the blue guides. If it’s a forward-facing seat, thread the seatbelt through the red guides.

ChildCarSeats.org.uk advises that as you tighten the seatbelt, push your weight into the seat to make sure it’s securely held, and make sure there’s no slack.

Some seats have a lever or button to tighten the seatbelt once it’s in place. If the seat has a lock, this prevents the belt from slipping once it’s been tightened.

Finally, make sure the seatbelt buckle is not resting on the frame of the child seat, otherwise there’s a risk of ‘buckle crunch’.

Isofix child car seats

Isofix car seats can be fixed on to metal attachments, which are now found in most cars. They’re an easy way of clicking car seats in and out of cars. If your car doesn’t have the metal attachments already built in, you can buy them and attach them to a car seat.

If you don’t know if your car has Isofix points, it’s easy to find out. Have a look in the car’s handbook or ask the manufacturer.

If it does, then check if your Isofix seat is approved for your car. This info could be on the seat itself, or on the car seat manufacturer’s website.

If you have a compatible car, using an Isofix child car seat is simple:

  • Find the 2 anchor points at the back of the rear passenger seat
  • Extend the arms of the car seat base
  • Slide the arms into the anchor points until they lock
  • Push the car seat back as far as it can go

There are usually indicators that tell you when the seat is secure. It’s important to check the instructions of your car seat as they tell you what and where these indicators are.

Some car seats have a third anchor – a strap that secures to the back of the passenger seat. This adds an extra level of stability to the car seat.

If it's an Isofix booster seat you need to install, some rules apply. Just make sure to check the instructions if you need any extra help.

i-size child car seats

These seats also fit into the car's Isofix points. Again, you need to check if the seat is approved for your particular car in the same way you do with Isofix seats.

But there are fewer models of car that are i-size approved, although the number is expected to increase.

How do I fit a car seat with a seat belt?

The specifics of how to fit a car seat with a seat belt vary depending on what type of seat you have and the type of car.

You need to check your car seat's instructions for the best way to fit it this way.

Should I get a rear-facing or a forward-facing seat?

The law says your child must be in a rear-facing seat until they weigh more than 9kg.

But the current safety advice is to keep your child rear-facing for as long as possible, or at least until they weigh 18kg.

Studies have shown that rear-facing seats are safer than forward-facing ones.

Should I buy a second-hand car seat?

No – you should never do this.

Even if it looks to be in good nick, you can’t be sure that a second-hand car seat hasn’t been in an accident. If it has, that could make it unsafe.

It might not have been in an accident, but it could have become damaged through wear and tear.

Even if you trust the person who is selling or giving it to you, neither of you can be sure that it’s 100% fit for purpose.

So it's always best to buy a new car seat. That way you can be sure that it meets the right safety standards.

Similarly, if you damage your car seat and it’s not covered under your car insurance, don’t cut corners – buy a replacement straight away.

Can I recycle my old car seat?

At the moment, there’s no real way to recycle car seats.

To make the seats safe and durable, they’re made of a mixture of materials that make recycling difficult.

Get in touch with your local recycling centre to see if they can recycle parts of the car seat.

The parts that can’t be recycled have to be thrown away. Don’t give it to a charity shop or try to sell it on a listings website.

When you do throw the car seat out, clearly write ‘unsafe’ or ‘expired’ on it somewhere to lessen the risk of someone else finding it and using it.