When can a child use an adult seat belt?

A child can use an adult seat belt from their 12th birthday or once they reach 135 cm tall, whichever happens first. The belt must be worn where one is fitted.

Who is responsible for a child under 14?

The driver is responsible for making sure a child under 14 uses the correct restraint or seat belt required by law.

Can an approved child seat go on a side facing seat?

No. GOV.UK says a child car seat must not be fitted on a side facing vehicle seat.

Child car seats

Child car seat law and seat checker

Which restraint does the law require?

The result applies the statutory age and height boundary, then shows the approval basis that must match the seat label.

AgeyearsHeightcmWeightkg

Child car seat

Approved child car seat required

Approved seat basisUse an R129 seat within its labelled height and weight limits or an ECE R44 seat within its labelled weight group: R129 or ECE R44
R44 weight groupsA listed group is only usable when the particular seat label covers the child and the vehicle.: Group 1, Group 2
R129 facing ruleAn R129 height based seat may face forward once the child is over 15 months old if its label permits it: Forward facing permitted
Front seat and airbagA suitable forward facing restraint may be used in front under the R129 or R44 rules. A rear facing baby seat still requires the frontal airbag to be deactivated, and the seat and vehicle manufacturer instructions must be followed: Only with a suitable forward facing restraint

Calculation details

Assumptions

Jurisdiction: Great Britain child restraint rulesGOV.UK, Child car seats: the law (as of 10 September 2026)
Age is entered in years. Fifteen months is 1.25 years, and the child remains inside the rear facing R129 rule at exactly that age.

What is not included

The approval label and manufacturer instructions decide whether a particular restraint fits the child and vehicle.
Statutory exceptions for taxis, unexpected necessary short journeys and limited rear seat space are not applied by this checker.

Summary: In Great Britain, a child normally needs an approved child car seat until their 12th birthday or until they reach 135 cm, whichever happens first. The seat must match the child's height or weight and be fitted as its manufacturer directs.

Checked on 10 September 2026.

ECE R44 weight groups published by GOV.UK

ECE R44 child restraint groups by weight
Group	Child weight	Permitted seat types
0	0kg to 10kg	Lie flat carrier, rear facing carrier or rear facing seat with a harness
0+	0kg to 13kg	Rear facing carrier or rear facing seat with a harness
1	9kg to 18kg	Rear or forward facing seat with a harness or safety shield
2	15kg to 25kg	Rear or forward facing seat, high backed booster or cushion, using the approved restraint
3	22kg to 36kg	Rear or forward facing seat, high backed booster or cushion, using the approved restraint

The ranges overlap. A group match does not override the approval label or the manufacturer fitting instructions for the particular seat and vehicle.

The legal boundary is age or height

The law releases a child from the child seat requirement at the first of two events: reaching 135 cm or reaching their 12th birthday. From that point an adult seat belt must be worn where one is fitted.

Before that boundary, the approved restraint can be selected by height under R129 or by weight under ECE R44. The approval label and the limits printed by the manufacturer decide whether that particular seat is suitable.

The front seat has a specific airbag rule

A rear facing baby seat must not be fitted in front of an active frontal airbag. GOV.UK requires the front airbag to be deactivated before that seat is fitted, and the restraint must be installed according to its manufacturer instructions.

Common questions

When can a child use an adult seat belt?: A child can use an adult seat belt from their 12th birthday or once they reach 135 cm tall, whichever happens first. The belt must be worn where one is fitted.
Who is responsible for a child under 14?: The driver is responsible for making sure a child under 14 uses the correct restraint or seat belt required by law.
Can an approved child seat go on a side facing seat?: No. GOV.UK says a child car seat must not be fitted on a side facing vehicle seat.

Sources

Rules and figures were checked against these government pages on 10 September 2026.