Help Centre · MTD ITSA · 1 min read

Your details and National Insurance Number

Where your personal details go, and why your National Insurance Number is required before any submission.

Tax Optimiser Updated 25 Jun 2026

Before you can send anything to HMRC, your own details need to be on record. Open User Details from the menu.

The User Details screen: name, email, National Insurance Number, Personal UTR and address

National Insurance Number

Your National Insurance Number is how HMRC ties your quarterly updates and final declaration to you. It is required — the setup checklist will not show as complete, and submissions will not go through, until it is entered. It looks like two letters, six digits and a final letter (for example AB 12 34 56 C).

The rest of the record

  • Personal UTR — your 10-digit Unique Taxpayer Reference for Self Assessment. Useful to hold here for reference.
  • Name and address — your personal details, kept separate from any individual business’s trading address.
  • Tax code — used when estimating the tax due on your income.

Enter your details and press Save. You only need to do this once; you can come back and update it any time.

Next: Connecting to HMRC.

The short version

Your details and National Insurance Number — in brief

Your National Insurance Number identifies you to HMRC on every submission and is required before the setup checklist completes.

Your Personal UTR, name, address and tax code are held on the same User Details screen.

Enter the details once and save; you can update them at any time.