Form CA5403 is the paper route for asking HM Revenue and Customs to send you written confirmation of your National Insurance number. You download it from GOV.UK, fill it in, print and sign it, and post it with identity documents to HMRC’s National Insurance office in Newcastle. There is no fee. A confirmation letter usually arrives within about 10 working days of HMRC processing your request.1GOV.UK. National Insurance Enquiries
Try the Online Service First
HMRC treats CA5403 as a fallback. The quickest way to recover your number is the online lookup at GOV.UK: sign in (or create sign-in details), verify your identity with a passport or driving licence, and the number appears on screen straight away.2GOV.UK. Find Your National Insurance Number The HMRC app does the same and can save the number to your phone’s digital wallet.3GOV.UK. Download the HMRC App
If you can’t prove your identity online, HMRC will automatically post the number to the address on your record, which can take up to 10 working days.2GOV.UK. Find Your National Insurance Number The online service isn’t available if you live abroad, which is the situation where CA5403 becomes your only real option.
What the Form Asks For
CA5403 collects the personal details HMRC needs to match you against their National Insurance records. You’ll give your full legal name, any previous names (including those changed by marriage or deed poll), your date of birth, your current address, and previous addresses if you’ve moved recently. Fill in every field. Gaps tend to trigger follow-up letters and slow the whole thing down.
There is no fee. Your only cost is postage.
Fill It In, Print It, Sign It
You can open Form CA5403 on GOV.UK and type your details straight into the fields on screen.4GOV.UK. Get Your National Insurance Number by Post Typed entries are easier for HMRC to read than handwriting and less likely to cause a processing delay. If you don’t have a computer, print a blank copy and complete it by hand in clear capitals with black ink.
Once the form is complete, print it and sign the declaration by hand. HMRC requires an original handwritten signature, so don’t post it unsigned.4GOV.UK. Get Your National Insurance Number by Post There is no way to email, fax, or upload CA5403. The whole process is physical: type or write, print, sign, post.
Identity Documents to Send With It
GOV.UK tells you to include documents that confirm your identity along with the completed form.4GOV.UK. Get Your National Insurance Number by Post The guidance page doesn’t spell out which documents qualify, but HMRC’s internal staff guide expects at least one primary identification document. The strongest options are:
- A current passport
- A biometric residence permit, for non-UK nationals with permission to stay
- A full UK or Irish birth certificate (the full version, not the short-form extract)
- A certificate of naturalisation if you became a British citizen
Secondary documents can strengthen the application: a UK driving licence, a recent utility bill, council tax correspondence, a marriage certificate, or a letter from an employer.5GOV.UK. National Insurance Number Allocation: Staff Guide to Document Evidence Checks Send certified copies rather than originals wherever you can. HMRC does not guarantee the return of documents sent by post, and replacing a passport is far more trouble than reprinting a copy.
Where to Post It
Send the completed, signed form and your identity documents to:
National Insurance contributions and Employers Office
HM Revenue and Customs
BX9 1AN4GOV.UK. Get Your National Insurance Number by Post
Within the UK, standard Royal Mail postage is fine. Asking for a certificate of posting at the counter costs nothing and gives you a dated receipt, which is worth having when identity documents are in the envelope.
Posting From Outside the UK
If you’re mailing from abroad, add “United Kingdom” as the final line of the address. From the United States, USPS offers Priority Mail International (typically 6 to 10 business days) and Priority Mail Express International (typically 3 to 5 business days), both with tracking.6USPS. International Shipping and Mailing Costs depend on weight and origin, so use the USPS price calculator for an exact figure. A customs form is required for international packages, though a standard letter-sized envelope may qualify as a letter rather than a package depending on weight.
How Long It Takes
HMRC says your National Insurance number will be posted to you and can take up to 10 working days to arrive.1GOV.UK. National Insurance Enquiries That clock starts once HMRC has received and processed your form, not from the day you post it. If you’re sending from overseas, add international mail transit time on both legs.
The confirmation arrives as a physical letter to the address you gave on the form. HMRC will not read your National Insurance number out over the phone, so calling won’t shortcut the wait. The phone line can confirm the status of your request, but the number itself always comes by post.1GOV.UK. National Insurance Enquiries
You Can’t Use It for Someone Else
CA5403 is for individuals requesting their own National Insurance number. You can’t use it to obtain another person’s number. HMRC’s disclosure rules do allow employers and pension providers to verify that a National Insurance number matches a name and date of birth, but only where there’s a legitimate business need and no suspicion of fraud.7GOV.UK. Information Disclosure Guide – IDG40440 – Sharing Information Outside of HMRC That verification runs through the employer’s own HMRC channels, separately from CA5403.