Self Assessment: register a partnership for Self Assessment (SA400)

Use the online forms service or postal forms to register a new partnership for Self Assessment.


Print and fill in by hand (PDF version)

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Use the SA400 to register a new partnership for Self Assessment. The partner nominated by the partnership to receive and submit partnership returns must sign the form.

You can register by:

  • using the online service
  • filling in the on-screen print and post form and sending it to HMRC

To register using the online service, you’ll need:

  • your Unique Taxpayer Reference (UTR) number or VAT reference number found in your business tax account
  • a Government Gateway user ID and password ― if you do not have a user ID, you can create one when you use the service

You can add the UTR or VAT reference number from the homepage of your business tax account.

If you use the online service to register, you’ll get a reference number to track the progress of your registration.

If you have problems opening the online forms you can use the PDF version. You’ll have to print this and fill it in by hand before posting it to HMRC.

Before you start

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After you’ve registered

We’ll usually contact you within 21 days of receiving your form but may take longer during busy periods.

If you registered online, you may be able to get your Unique Taxpayer Reference (UTR) sooner using the HMRC App or your business tax account.

If we have not contacted you after 3 weeks, you can check when you can expect a reply.

Authorise a tax agent (64-8)
Use this form to tell HMRC that you give authorisation for someone to act on your behalf for individual or business tax affairs.

Published 30 April 2014
Last updated 12 February 2024 + show all updates
  1. Information has been added explaining what will happen after you’ve registered.

  2. Added translation

  3. The phone numbers and web links on the form has been updated.

  4. Details section has been updated with additional requirements for registering a new partnership online.

  5. Newly Self-Employed Helpline telephone number has been updated.

  6. An online service is now available.

  7. First published.