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HMRC letter codes · National Insurance (CA)

CA4361National Insurance refund letter

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

In short

GOV.UK lists the CA4361 as a letter from HMRC, sent if it thinks you may have paid too much in your National Insurance contributions.

“Letter CA4361 … HMRC will contact you by letter if we think you may have paid too much in your National Insurance contributions.”

GOV.UK: Check if a letter you’ve received from HMRC is genuine · checked 14 October 2026

Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CA4361. Each fact has its source and the day it was checked beside it.

When HMRC sends it

GOV.UK's page on the CA4361 form says you can only apply for a refund if you have received a letter from HMRC telling you that you may be due a refund.

“You can only apply if you’ve received a letter from HMRC telling you that you may be due a refund.”

GOV.UK: Apply for a refund of Class 1 National Insurance contributions · checked 14 October 2026

What it asks

GOV.UK says the CA4361 letter asks you for information about your past employment, and tells you which tax years HMRC needs information for.

“We will ask you for information about your past employment. … We will tell you which tax years we need information for”

GOV.UK: Check if a letter you’ve received from HMRC is genuine · checked 14 October 2026

GOV.UK says the CA4361 letter asks you to reply by completing the online form or by completing and posting the paper form attached with the letter.

“The letter will ask you to reply by either: … completing the online form … completing and posting the paper form attached with the letter”

GOV.UK: Check if a letter you’ve received from HMRC is genuine · checked 14 October 2026

GOV.UK says the claim reference number on a CA4361 letter is not your National Insurance number, and that you will find it at the top of the letter, underneath your National Insurance number, shown as Reference.

“Your claim reference number is not your National Insurance number. You’ll find it at the top of the letter, underneath your National Insurance number, shown as ‘Reference’.”

GOV.UK: Apply for a refund of Class 1 National Insurance contributions · checked 14 October 2026

How to send it or apply

GOV.UK says that to apply by post you fill in the CA4361 form sent to you and send it to the address shown on the letter.

“Apply by post … Fill in the CA4361 form sent to you and send it to the address shown on the letter.”

GOV.UK: Apply for a refund of Class 1 National Insurance contributions · checked 14 October 2026

GOV.UK says that if your CA4361 letter has a claim reference number, you can apply online or by post.

“If your letter has a claim reference number, you can apply online or by post.”

GOV.UK: Apply for a refund of Class 1 National Insurance contributions · checked 14 October 2026

Free help and HMRC contacts

GOV.UK says that if you have lost the CA4361 form sent to you, you can contact the National Insurance helpline.

“If you’ve lost the form sent to you, contact the National Insurance helpline.”

GOV.UK: Apply for a refund of Class 1 National Insurance contributions · 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.