How to Find Your Lost National Insurance Number Online in the UK: HMRC App, Tax Account and Postal Options

Lost your National Insurance (NI) number? You can usually find it without paying a third-party service or waiting for a letter. In the UK, HM Revenue & Customs (HMRC) lets eligible users view their number through the HMRC app or a Personal Tax Account, and download a confirmation letter. If online access is not possible, you can check existing paperwork or request written confirmation by post. This guide explains each route, what to do when verification fails, and how to avoid common mistakes.

Start with the official service: GOV.UK – Find your National Insurance number. The exact sign-in and identity checks can change; always follow the current prompts on GOV.UK rather than sharing personal details with an unofficial website.

Quick answer: the fastest ways to recover your NI number

1. Look on a recent payslip, P60, or letter about tax, benefits or pensions.
2. Open the official HMRC app and sign in to see your NI number and obtain confirmation.
3. Sign in to your Personal Tax Account and look for your National Insurance number.
4. Check Apple Wallet or Google Wallet if you previously saved the number there.
5. If these methods fail, use the official postal confirmation process.

A National Insurance number normally has two letters, six digits and one final letter. GOV.UK gives an example of the format, but do not mistake an example for your own number. Your number generally stays the same throughout your life.

Method 1: Find your National Insurance number in the HMRC app

For many UK residents with access to an eligible phone and an HMRC sign-in, the official app is the most convenient option. Download it only through the app-store links on GOV.UK’s HMRC app page, not through advertisements or messages.

1. Open the official HMRC app on your iPhone or Android phone.
2. Sign in using your existing HMRC online-services credentials, or follow the in-app registration process if you do not have them.
3. Complete any identity or security checks requested by HMRC.
4. Go to the area showing your personal details and National Insurance information; wording can vary by app version.
5. View your number, then use the option to save or download a confirmation letter if you need a document for an employer.
6. If offered, save the number to Apple Wallet or Google Wallet for future access.

HMRC says the app supports a six-digit PIN, fingerprint or facial recognition for later sign-ins after setup. Biometric access does not replace the initial account and identity requirements. If the app refuses access, try the Personal Tax Account method below rather than repeatedly submitting different personal details.

Method 2: Use your HMRC Personal Tax Account on a computer or phone

You do not have to install an app. The official Personal Tax Account provides access to HMRC records and includes a way to find your NI number. The account may request identity verification, which helps prevent other people from accessing your records.

1. Visit gov.uk/personal-tax-account directly.
2. Choose the sign-in option and enter the credentials requested by the current government service.
3. Complete any additional authentication or identity verification prompts.
4. Locate the National Insurance number section in your account.
5. Use the available option to download or save a confirmation letter as a PDF.
6. Check that the name and number shown belong to you before sharing the letter with a legitimate employer.

If you cannot get into the account, check whether you are using the correct sign-in method and whether your browser is blocking necessary cookies. Do not assume that a failed sign-in means you have no NI number; it usually means you cannot access the online record at that moment.

Method 3: Check paperwork you already have

Before waiting for post, search your own records. An employer-issued payslip or P60 is often faster than setting up an account, especially if you are starting a job soon. Tax, pension and benefit letters may also show the number.

If you are using a payroll portal, download the payslip securely rather than emailing a screenshot to yourself or another person. Store your NI number carefully because it can be misused when combined with other personal information.

Method 4: Request written confirmation by post with CA5403

If you already have an NI number but cannot retrieve it online or from documents, HMRC provides form CA5403 for postal confirmation. This is not the application route for someone who has never been issued a number.

1. Open the current GOV.UK guidance for obtaining your NI number by post.
2. Follow the online form instructions to prepare the CA5403 print-and-post request.
3. Print the completed form and sign the declaration.
4. Include the identity documents requested by the current form instructions, if applicable.
5. Send it to the HMRC address printed in the current official guidance; the listed destination is National Insurance contributions and Employers Office, HM Revenue and Customs, BX9 1AN.
6. Allow for postal delivery and processing, and use HMRC’s official contact guidance if you need to check a delay.

The HMRC National Insurance enquiries page says a number requested through its assistance route may be sent by post and can take up to 10 working days to arrive. That is guidance rather than a guarantee for every postal form or address. Do not promise an employer a fixed delivery date.

What if you are outside the UK?

Your NI number does not normally change when you move abroad. Check existing UK payslips, P60s, tax correspondence and your available HMRC online account first. The HMRC app page notes special sign-in considerations for people without a UK address; eligibility and access may differ. If you cannot use the online route, consult the official GOV.UK finder and postal instructions rather than assuming an app or UK mobile number is mandatory.

Use the official finder to determine the route suitable for your circumstances. If a document needs to be sent abroad, confirm the accepted address and processing method with HMRC before posting sensitive original identification.

What if you have never had a National Insurance number?

A lost number and a number that has never been issued are different problems. If you lived in the UK during childhood, you may have received an NI number shortly before your 16th birthday. People arriving from overseas may already have one from previous work or benefit records; otherwise they may need to apply.

If you are certain you have never been allocated one, use the official Apply for a National Insurance number service and check the eligibility requirements. Do not use the CA5403 replacement route to try to create a new number. Also, an NI number is not itself proof of your identity or immigration status.

How to give your NI number to a new employer safely

An employer may ask for your NI number to help report payroll and tax information correctly. If you can sign in to HMRC, download the official confirmation letter. Check whether your employer accepts the PDF through its secure onboarding portal. You should not send identity documents or an NI number to an unfamiliar recruiter before verifying the organisation.

If your first payday is approaching and you still cannot locate the number, tell payroll promptly. Ask what information they need in the meantime and follow their formal onboarding process; do not invent a number, use a colleague’s number, or rely on a placeholder as if it were valid. The employer may need to follow its own HMRC payroll procedures.

Troubleshooting: the HMRC app or online account does not show your number

Can HMRC tell you your NI number over the phone?

No. GOV.UK explicitly states that HMRC cannot provide your NI number over the phone or via webchat. Staff may help you understand how to retrieve it or arrange postal confirmation, but do not expect them to read the number aloud. This is an important safeguard against impersonation. See the official finder and National Insurance enquiries.

Protect yourself from National Insurance number scams

• Type gov.uk addresses directly and inspect the full domain before signing in.
• Do not pay a website that claims it can reveal your NI number instantly; official routes are available.
• Never share one-time security codes, passwords or complete identity-document photos with unsolicited callers.
• Use a secure employer portal when sharing confirmation documents.
• If a suspicious message claims your NI number has been suspended, verify the claim independently through GOV.UK.

What your National Insurance number does—and does not—prove

Your NI number helps link your tax and National Insurance contribution records to the correct person. It is not a bank account number, a standalone identity document, a visa, or evidence that you have the right to work. Employers may require separate right-to-work checks. Losing a paper letter does not automatically mean you have lost the underlying number or need a replacement number.

Best recovery route by situation

Official sources and further reading

• GOV.UK: Find your National Insurance number — primary decision tool and recovery methods.
• GOV.UK: Download the HMRC app — app features and sign-in information.
• GOV.UK: Personal Tax Account — secure online access.
• GOV.UK: Get your National Insurance number by post — CA5403 and current postal process.
• GOV.UK: National Insurance enquiries — official assistance and postal expectations.
• GOV.UK: About your NI number — format and security.

Bottom line: Check a payslip or P60 first. If you can securely sign in, the HMRC app or Personal Tax Account is usually the quickest way to retrieve your NI number and obtain a confirmation letter. If online access fails, use the official GOV.UK postal process. Never rely on a paid unofficial lookup service.