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HMRC letter codes · Child Benefit (CH)

CH299Apply for extended Child Benefit

Last reviewed 14 October 2026 · How Tax Letters checks its facts

In short

GOV.UK says the CH299 online service is used to apply for an extension of Child Benefit if your child's under 18 and has left approved education or training.

“Use the online service (CH299) to apply for an extension of Child Benefit if your child's under 18 and has left approved education or training.”

GOV.UK: Apply for extension to Child Benefit · checked 14 October 2026

Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CH299. Each fact has its source and the day it was checked beside it.

What it asks

GOV.UK says the CH299 online service needs you to sign in to apply, and that if you do not already have sign in details you can create them.

“You’ll need to sign in to apply online. If you do not already have sign in details, you’ll be able to create them.”

GOV.UK: Apply for extension to Child Benefit · checked 14 October 2026

Time limits and rules

GOV.UK's page for CH299 says you could get extended Child Benefit for up to 20 weeks if your child is 16 or 17, has left approved education or training, and has either registered with a qualifying body or signed up to join the armed forces.

“You could get extended Child Benefit for up to 20 weeks if your child is 16 or 17, has left approved education or training, and has either: … registered for work, training or full-time education with a ‘qualifying body’ … signed up to join the armed forces”

GOV.UK: Apply for extension to Child Benefit · checked 14 October 2026

Free help and HMRC contacts

If you cannot find the answer in the official HMRC app, GOV.UK says to call HMRC on 0300 200 3100 with a question about Child Benefit, including one about a CH299 extension. Lines are open Monday to Friday, 8am to 6pm, closed bank holidays, and GOV.UK links to its call charges page.

“Call HMRC if you have a question about Child Benefit and you cannot find an answer in the official HMRC app. … Telephone: 0300 200 3100 … Opening times: Monday to Friday, 8am to 6pm. Closed bank holidays. … Find out about call charges”

GOV.UK: Child Benefit: enquiries · checked 14 October 2026

Free help first

These routes are described by GOV.UK, TaxAid and Citizens Advice themselves.

  • HMRC's extra supportHMRC offers extra support if your health condition or personal circumstances make it difficult to contact HMRC, for example a mental health condition, financial hardship or being treated in hospital.
  • Someone to deal with HMRC for youYou can authorise a friend, relative or voluntary organisation to talk to HMRC for you and help you fill in forms.
  • TaxAidTaxAid helps people with tax problems who cannot pay for advice. Tax Help for Older People merged with TaxAid in July 2025.
  • Citizens AdviceCitizens Advice gives confidential advice online, over the phone and in person, for free.