Help, I’ve lost my National Insurance Number

lost national insurance number

Everyone born in the UK gets a National Insurance number assigned to them for their sixteenth birthday. The combination of letters and numbers is completely unique to you. It becomes a hugely important piece of your personal identification. It is used by HMRC, DWP, your employers and other relevant government departments.

You”ll need it for everything related to you and your income tax including a claim for a tax rebate under PAYE.

Here’s what to do if you’ve lost yours.

Check all the places it might be:

Depending on your age, you may have it on an actual National Insurance card. These are credit card sized and used to be issued to everyone. You might have it tucked away somewhere and forgotten about it. These are no longer issued, but the number you have on there never changes.

Old paperwork

  • Any PAYE payslips
  • Letters from HMRC
  • Communication about tax or pensions
  • Letters about any benefits you receive
  • P60s
  • Other official paperwork from old employers

Remember, it doesn’t matter how old these documents are because your National Insurance number stays the same for your entire life.

Your national insurance number is totally lost

OK, no need to panic. There are three ways to locate your missing National Insurance number. Due to security, these are not immediate fixes. You can use your online Personal Tax Account, phone HMRC or use Form CA5403.

Personal Tax Account

This is part of HMRC’s big Making Tax Digital plan. Your Personal Tax Account is just for you and is designed so that you can manage your tax records more efficiently. As well as finding your National Insurance number, you can do other things like update your details and claim a tax refund.

You access it through your Government Gateway ID in order to verify your identify for security purposes. Once you’ve set up your Personal Tax Account, you can see your NI number and print a confirmation letter for your files.

You can look at your personal tax account whenever is convenient to you and on any device.

Form CA5403

This is an online form that you must complete on screen and the print to post to HMRC. You cannot start, save it and go back to it. It must be started and finished all in one go. This means getting all your details gathered together before you start.

You will be asked a series of questions. Depending on how you answer, you might have to send additional official documents. This is to prove your identity and secure your information.

It could be one or two of the following:

  • birth certificate
  • passport
  • full or provisional driving licence
  • adoption certificate
  • home office or travel document
  • work permit
  • certificate of naturalisation
  • marriage or civil partnership
  • certificate of service in Her Majesty’s Forces or merchant navy
  • identity or medical card”

This list is taken straight from GOV.UK’s Form CA5403 guidance page.

Once you’ve completed the form and gathered any evidence required, post it to:

National Insurance contributions and Employers Office

HM Revenue and Customs


You will then receive your National Insurance number from HMRC by post. This process can take up to 15 days.

You can phone HMRC

HMRC have a dedicated National Insurance helpline on 0300 200 3500. This open on week days from 8am to 8pm and Saturdays from 8am to 4pm. Staff on this helpline are specifically trained to help people who do not have a National Insurance number. This may be because it has not been issued at the time you turn 16, you are not able to get an online Personal Tax Account or you have lost your NI number.

Don’t expect to be told your NI number instantly over the phone. You will be asked a series of questions, so get all your available personal information ready before you call, then your National Insurance number will be sent to you in the post. Plan for it to take around 15 working days.


Tony Shanks
Operations Director
Member of the ATT

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