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If you already have a National Insurance number
If you’ve forgotten your National Insurance number or need a letter confirming it, you can use your personal tax account to view or download, print, save or share a letter with it on.
If you do not have a personal tax account, you can register for one now.
If you’re unable to register for a personal tax account
Fill in part 1 of form CA5403 on-screen, then print and post it to HMRC.
If you cannot provide all the information asked for in part 1 you may have to fill in part 2 as well. Part 1 will tell you if you need to print, then fill in part 2. If you need to fill in parts 1 and 2 of CA5403 send them to HMRC together.
It can take up to 15 days to get your National Insurance number by post.
Send the print and post form to:
National Insurance contributions and Employers Office
HM Revenue and Customs
Before you start using the CA5403 postal form
If you’re using an older browser, such as Internet Explorer 8, you’ll need to update it or use a different browser. Find out more about browsers.
You’ll need to fill in the CA5403 fully before you can print it. You cannot save a partly completed form so gather all your information together before you start to fill it in.