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To view your National Insurance number or get a letter confirming it, you can either:
use the online service (sign in or set up a Government Gateway user ID)
fill in the form, print it off and post it to HMRC.
To use the online service, you need a Government Gateway user ID and password. If you do not have a user ID, you can create one when you use the service.
If you cannot use the online service
Fill in part 1 of form CA5403 on-screen, then print and post it to HMRC.
If you cannot give us 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 also need to print, then fill in part 2. If you need to fill in parts 1 and 2 of CA5403 send them back together.
It can take up to 15 days to get your National Insurance number in the post.
Send the print and post form to:
National Insurance contributions and Employers Office
HM Revenue and Customs
Before you start using the CA5403 part 1 postal form
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You’ll need to fill in the CA5403 part 1 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.