How to Find Your National Insurance Number (Online, App or Post)

The quickest way to find your National Insurance number is the HMRC app or your Personal Tax Account on GOV.UK: sign in, and the number is shown on screen where you can save or print a confirmation letter straight away. If you can't get online, it is printed on your payslips, your P60 and most letters from HMRC or the Department for Work and Pensions — and HMRC will post a written confirmation if you ask.

Your number never changes and it is never reissued, so "lost" only ever means you need to be reminded of it. Every official route is free.

Key points

• An NI number looks like QQ 12 34 56 A — two letters, six digits, then a final letter A, B, C or D.
• Fastest routes: the HMRC app, or the "find a lost National Insurance number" service in your Personal Tax Account.
• Offline, check a payslip, P60, P45, tax code letter, State Pension letter or Child Benefit letter.
• By post, HMRC sends written confirmation to your registered address — never to a new address you supply over the phone.
• Children living in the UK usually get a number automatically before their 16th birthday if Child Benefit was claimed for them.

Where your National Insurance number is printed

Before you set up any online account, have a look through your paperwork. The number appears on a surprising number of documents, and finding it there takes seconds.

What a valid number looks like

The format is two prefix letters, six digits and a single suffix letter — for example AB 12 34 56 C. The suffix is always A, B, C or D. If what you have found has a different shape (for example it starts "TN" or has no final letter), it is not a usable NI number and you should confirm the real one with HMRC.

Find your NI number in the HMRC app

The HMRC app is the fastest option for most people. Download it from the official app store listing, then:

1. Sign in with your Government Gateway user ID and password, or set up sign-in details if you have none.
2. Confirm your identity — usually a passport, driving licence, recent payslips or P60 figures, plus a code sent to your phone.
3. Your National Insurance number is displayed on the main screen or under your personal details.
4. Choose the option to save or share a confirmation, which produces a PDF letter you can send to an employer, letting agent or student finance provider.

Once you are in, it is worth staying a moment longer. The app also shows your tax code, your pay and tax to date, and your National Insurance record — the list of years that count towards your State Pension.

Find your NI number online without the app

If you would rather use a browser, the GOV.UK service find a lost National Insurance number does the same job through your Personal Tax Account. You will need the same identity evidence: a Government Gateway account plus one or two documents such as a UK passport, a photocard driving licence, or details from a recent payslip, P60 or Self Assessment return.

The service shows the number on screen and lets you download a confirmation letter immediately. There is no charge, and no commercial site can get you the number any faster — if a website asks for a fee to "retrieve" or "apply for" your NI number, it is not an official service.

If you can't pass the identity checks

Identity verification is the usual sticking point, especially if you have no UK passport, a very short credit history or a recently changed name. If the checks fail, you have two fallbacks: ask a previous or current employer's payroll team to confirm the number they hold for you, or request written confirmation from HMRC by post (below). HMRC will not read the number out over the phone.

Get your National Insurance number by post

To receive written confirmation, complete form CA5403. You can fill it in on screen, print it and post it to the National Insurance contributions office address shown on the form, using the guidance at GOV.UK: get your National Insurance number in writing. Alternatively, call the National Insurance enquiries helpline and ask them to post it.

Two things to expect. First, allow time — HMRC posts the letter rather than emailing it, and delivery takes a couple of weeks. Second, the letter goes to the address HMRC already holds for you, which is a deliberate anti-fraud step. If you have moved, update your address in your Personal Tax Account first, or tell HMRC in writing.

Your child's National Insurance number

If your child lives in the UK and a Child Benefit claim was made for them, they are normally allocated a number automatically before they turn 16. Historically HMRC posted a letter shortly before the 16th birthday; the number is now most reliably found by the young person signing in to the HMRC app or their own Personal Tax Account once they are 16.

Points that catch parents out:

• You cannot see your child's number in your own account. It belongs to them, not to your Child Benefit claim, and the reference on your Child Benefit letters is your own NI number.
• If no Child Benefit was ever claimed — for example the claim was declined or never made — the child may not have been allocated a number and will need to apply.
• Applying from scratch uses the service at GOV.UK: apply for a National Insurance number, which is also the route for adults arriving in the UK who have never had one.
• Turning 16 does not mean paying NI. Class 1 National Insurance only starts once weekly earnings pass the primary threshold, which is £12,570 a year for 2026/27.

Use the number to check what really matters: your NI record

The number itself is just a reference. What it unlocks is your National Insurance record — the year-by-year list showing which tax years count towards the State Pension and which have gaps.

You can view it through GOV.UK: check your National Insurance record. For 2026/27 the arithmetic behind that record looks like this:

• Employees pay Class 1 NI at 8% on earnings between £12,570 and £50,270, then 2% above £50,270.
• Self-employed people pay Class 4 at 6% on profits between £12,570 and £50,270, then 2% above, with voluntary Class 2 at £3.65 a week available below the £7,105 small profits threshold.
• The full new State Pension is £241.30 a week and generally needs 35 qualifying years.

Worked example. Suppose your record shows one gap year. Each qualifying year is worth roughly £241.30 ÷ 35 = £6.89 a week, or about £358 a year of extra State Pension. Filling that gap with voluntary Class 3 contributions at £18.40 a week costs 52 × £18.40 = £956.80. On those figures the contribution pays for itself after about two years and eight months of drawing the pension (£956.80 ÷ £358 ≈ 2.7). Whether a specific gap can be filled, and at what rate, depends on the year in question and on how many years you already have, so check your own forecast before acting.

National Insurance works the same way across the UK. Scotland sets its own income tax rates on non-savings income, but NI numbers, NI rates and NI thresholds are identical in England, Wales, Scotland and Northern Ireland.

What to do next

Once you have the number in hand, put it to work. Use the State Pension forecast tool to see what your record is currently on track to pay and whether any years are missing, and the National Insurance calculator to check the contributions coming out of your pay or profits are right for 2026/27. Keep a copy of the confirmation letter somewhere safe — and never share the number in response to an unexpected call, text or email.