HMRC letter codes · National Insurance (CA)
National Insurance (CA) letters and forms, explained by code
Last reviewed 14 October 2026 · How Tax Letters checks its facts
Codes on HMRC's National Insurance letters and forms. Most start CA; CF83 is here too. Each code page reports what HMRC, GOV.UK or a recognised body publishes about it, with the source and the day it was checked beside each fact.
Every National Insurance (CA) code
- CA5603 Apply to pay voluntary National Insurance contributionsGOV.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.
- CA5403 Request your National Insurance number by postGOV.UK says to use form CA5403 to request a copy of your National Insurance number by post.
- CA2490 Home Responsibilities Protection eligibility letterGOV.UK lists the CA2490 as a letter about Home Responsibilities Protection eligibility.
- CA4361 National Insurance refund letterGOV.UK lists the CA4361 as a letter from HMRC, sent if it thinks you may have paid too much in your National Insurance contributions.
- CA72A Defer National Insurance when you have more than one jobGOV.UK says employees with more than one job may be allowed to defer (delay) paying Class 1 National Insurance on their other jobs, and that form CA72A is the form to send.
- CA8480 Refund of self-employed National InsuranceGOV.UK says to use the online service or postal form CA8480 to apply for a refund of Class 2 National Insurance contributions.
- CF83 Pay voluntary National Insurance for periods abroadGOV.UK's CF83 page says you can apply to pay voluntary National Insurance contributions for periods abroad to fill gaps in your National Insurance record.
- CA5601 Pay self-employed National Insurance by Direct DebitGOV.UK says form CA5601 is for arranging to pay self-employed Class 2 National Insurance contributions by Direct Debit, and adds: “This only applies if you have a specific job.”
- CA5610 Refund of self-employed National Insurance, profits-basedGOV.UK lists the CA5610 as the form to apply for a refund of Class 4 National Insurance contributions.
- CA307 Refund of UK National Insurance paid while working abroadGOV.UK lists the CA307 as the form to apply for a refund of UK National Insurance contributions paid while working abroad.
- CA82 Appeal a National Insurance credits decisionGOV.UK says to use form CA82 to appeal an HMRC decision on National Insurance credits.
- CA3822 Certificate of coverage for working temporarily abroadGOV.UK lists the CA3822 as the form to apply for a certificate confirming you will pay UK National Insurance when working temporarily abroad, and its page says to use it if you are going to work temporarily in an EU country, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland.
- CA3837 Certificate for working temporarily abroad while self-employedGOV.UK lists the CA3837 as the form to apply for a certificate confirming you will pay UK National Insurance while self-employed abroad temporarily, and its page describes it as for a self-employed individual working temporarily in an EU country, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland.
- CA8421 Certificate for working in several countriesGOV.UK lists the CA8421 as the form to apply for a certificate confirming you pay UK National Insurance when working in 2 or more countries.
Information, not advice: these pages report what HMRC and GOV.UK say about each code. Your own letter comes first.
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Other series
- Self Assessment (SA)SA1, SA401, SA250, SA316, SA100 and more
- Corporation Tax (CT)CT600, CT603, CT41G, CT41G (Clubs), CT208 and more
- VATVAT1, VAT1A, VAT1B, VAT2, VAT7 and more
- Child Benefit (CH)CH2, CH24A, CH105, CH995, CH459 and more
- Tax credits (TC)TC600, TC602, TC603D, TC603R, TC603UR and more
- Debt and payment letters (IDMS)IDMS99, IDMS99P, OCA43
- One-to-many lettersNISPAR1MM, LCL2REG2MM, CompC1LPLRMM, CompC1LPLR(A)MM, HEIPO2MM and more
- Compliance check factsheets (CC/FS)The factsheets HMRC's compliance letters name.
- Every HMRC letter codeAll the series on one page.
- GOV.UK: Apply to pay voluntary Class 3 National Insurance contributions (checked 14 Oct 2026)
- GOV.UK: Pay voluntary Class 3 National Insurance (checked 14 Oct 2026)
- GOV.UK: Pay voluntary Class 3 National Insurance: Set up regular payments (checked 14 Oct 2026)
- GOV.UK: Get your National Insurance number by post (checked 14 Oct 2026)
- HMRC National Insurance manual: NIM39205 - National Insurance numbers (NINOs): confirming a NINO: confirmation by individual - form CA5403 (checked 14 Oct 2026)
- GOV.UK: Check if a letter you’ve received from HMRC is genuine (checked 14 Oct 2026)
- GOV.UK: Apply for Home Responsibilities Protection (checked 14 Oct 2026)
- GOV.UK: Apply for a refund of Class 1 National Insurance contributions (checked 14 Oct 2026)
- GOV.UK: Defer your National Insurance (checked 14 Oct 2026)
- GOV.UK: Defer payment of Class 1 National Insurance contributions (CA72A) (checked 14 Oct 2026)
- GOV.UK: National Insurance: enquiries (checked 14 Oct 2026)
- GOV.UK: Apply for a refund of Class 2 National Insurance contributions (checked 14 Oct 2026)
- GOV.UK: Apply to pay voluntary National Insurance contributions for periods abroad (CF83) (checked 14 Oct 2026)
- GOV.UK: Apply to pay self-employed National Insurance by Direct Debit (checked 14 Oct 2026)
- GOV.UK: Apply for refund of Class 4 National Insurance contributions (CA5610) (checked 14 Oct 2026)
- GOV.UK: Apply for a refund of UK National Insurance contributions paid while working abroad (CA307) (checked 14 Oct 2026)
- GOV.UK: Appeal a National Insurance credits decision (CA82) (checked 14 Oct 2026)
- GOV.UK: Apply for a certificate confirming you will pay UK National Insurance when working temporarily abroad (CA3822) (checked 14 Oct 2026)
- GOV.UK: Apply for a certificate to confirm you will pay UK National Insurance while self-employed abroad temporarily (CA3837) (checked 14 Oct 2026)
- GOV.UK: Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421) (checked 14 Oct 2026)
- GOV.UK: Get help from HMRC if you need extra support (checked 7 Oct 2026)
- GOV.UK: Appoint someone to deal with HMRC on your behalf (checked 7 Oct 2026)
- TaxAid: About us (checked 8 Oct 2026)
- Citizens Advice: About us (checked 7 Oct 2026)