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HMRC letter codes · National Insurance (CA)

CA5603Apply to pay voluntary National Insurance contributions

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

In short

GOV.UK says CA5603 is the form to use to find out when to make voluntary Class 3 National Insurance contribution payments, how to apply to make a payment and how to pay.

“Use form CA5603 to find out when you should make voluntary Class 3 National Insurance contribution payments, how to apply to make a payment and how to pay.”

GOV.UK: Apply to pay voluntary Class 3 National Insurance contributions · checked 14 October 2026

Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CA5603. Each fact has its source and the day it was checked beside it.

What it is

GOV.UK says the CA5603 form explains how paying could help you, who can make payments, time limits and how to pay.

“Paying voluntary contributions can close gaps in your National Insurance record, however there are time limits on when you can make payments. … This form explains: … how paying could help you … who can make payments … time limits … how to pay”

GOV.UK: Apply to pay voluntary Class 3 National Insurance contributions · checked 14 October 2026

GOV.UK’s guide to paying voluntary Class 3 National Insurance calls the CA5603 the regular payments application form, in its part on making regular payments to cover a shortfall in your National Insurance record.

“you can make regular payments to cover the shortfall … download and send the regular payments application form (CA5603)”

GOV.UK: Pay voluntary Class 3 National Insurance · checked 14 October 2026

What it asks

GOV.UK says that to set up monthly Direct Debit payments of voluntary contributions you download and send the regular payments application form (CA5603) to HMRC, and the address is on the form.

“To set up monthly payments, download and send the regular payments application form (CA5603) to HM Revenue and Customs (HMRC). The address is on the form.”

GOV.UK: Pay voluntary Class 3 National Insurance: Set up regular payments · checked 14 October 2026

GOV.UK says that to pay voluntary contributions quarterly you can use the regular payments application form (CA5603), select quarterly payments, then post it to the address on the form.

“If you want to pay quarterly, you can: … use the regular payments application form (CA5603), select quarterly payments, then post it to the address on the form”

GOV.UK: Pay voluntary Class 3 National Insurance: Set up regular payments · checked 14 October 2026

Time limits and rules

GOV.UK’s guide to paying voluntary Class 3 National Insurance, which names the CA5603, says you can only pay for gaps in your National Insurance record for the past 6 tax years, and that “The deadline is 5 April each year.”

“You can only pay for gaps in your National Insurance record for the past 6 tax years. The deadline is 5 April each year.”

GOV.UK: Pay voluntary Class 3 National Insurance · checked 14 October 2026

Free help and HMRC contacts

GOV.UK, in its guide that names the CA5603, says that if you are below State Pension age you can contact the Future Pension Centre to find out if you will benefit from paying voluntary contributions.

“If you’re below state pension age, you can also contact the Future Pension Centre to find out if you’ll benefit from paying voluntary contributions.”

GOV.UK: Pay voluntary Class 3 National Insurance · 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.