NI Number
A unique personal reference number issued to UK residents to track their National Insurance record, in the format two letters, six digits, one letter (e.g., AB123456C). Every person in the UK who works or claims state benefits needs an NI number. Employers use it to report earnings and deductions to HMRC, ensuring your State Pension entitlement is correctly recorded.
How it works
You're normally issued an NI number automatically as a teenager if you live in the UK and your parent or guardian receives Child Benefit for you, arriving by post rather than requiring an application. If you move to the UK from abroad and need to work, you'll usually need to apply for one separately, and you can often start work before it arrives as long as you can prove your right to work by other means.
Your NI number stays with you for life and never changes, even if you change your name, move address, or switch between employment and self-employment multiple times — it's the single reference HMRC and the Department for Work and Pensions use to link all of your National Insurance contributions and benefit claims together across your working life. You'll need to quote it when starting a new job, applying for benefits, opening a workplace pension, or contacting HMRC or the DWP about almost anything.
An NI number is not proof of your right to work in the UK or a form of identification in the way a passport is — having one doesn't itself confer eligibility to work, and someone with the right to work can validly be employed while their NI number application is still being processed.
Frequently asked questions
What do I do if I've lost my NI number?
You can find it on previous payslips, P60s, or letters from HMRC, or request confirmation of it from HMRC directly — you can't apply for a brand new one, since your original number stays valid for life.
Can I work in the UK without an NI number?
Yes, temporarily — you can start a job while your application is being processed as long as you can otherwise prove your right to work, though you'll need to give your employer the number once it arrives.
Does my NI number change if I move abroad and come back?
No — your NI number is permanent and doesn't change regardless of how long you live outside the UK or how many times you leave and return.
Related Terms
National Insurance
A system of compulsory contributions paid by employees, employers, and the self-employed that funds state benefits including the State Pension, Statutory Sick Pay, and Maternity Pay.
Class 1 National Insurance
National Insurance contributions paid by employees and employers on earnings above the Primary Threshold.
PAYE
Pay As You Earn — the system by which employers deduct income tax and National Insurance directly from employees' wages before paying them, and remit the deductions to HMRC on their behalf.