Welcome to the 123 Sheets Setup Guide
Please follow the instructions below to correctly set up 123 Sheets for Making Tax Digital (MTD) for Income Tax.
If you experience any problems, please contact us at support.team@123sheets.co.uk.
Step 1
Register for Making Tax Digital for Income Tax (if you haven’t already)
If you have not yet registered, please sign up for Making Tax Digital for Income Tax here: https://www.gov.uk/guidance/sign-up-your-business-for-making-tax-digital-for-income-tax
Important:
If you are starting MTD for Income Tax from April 2026, please ensure you register for the tax year “2026/27” when selecting from the available options.
HMRC has informed us that many taxpayers accidentally sign up for the wrong tax year. Correcting this with HMRC can take a considerable amount of time.
Step 2
Completing the Software Setup
Next, you will need to purchase a licence from us.
To do this, use the top menu:
- Click “Settings”
- Then select “Taxpayer Details”
Select the “Licence Upgrade” you need. Select an MTD Income Tax “Licence Upgrade” of “1 Nat. Ins. No.” for a single taxpayer, or “10” for 2 to 10 taxpayers. Leave the “VAT” box unticked, unless you wish to purchase a licence to file VAT Returns as well, as a VAT Registered trader.
The licence is instantly active on purchase. You can add additional National Insurance Numbers (NINOs) by:
- Going to the “Taxpayers” page in the top menu
- Clicking the green “Add Taxpayer” button (top right)
Please note that the ability to add additional taxpayers is only available if you have purchased a 10-taxpayer licence or higher.
Step 3
Authorising 123 Sheets to Provide MTD for Income Tax Services
To authorise our software, you will be temporarily redirected to the HMRC website, where you will log in using your Government Gateway account. Once the process is complete, HMRC will return you to our website automatically.
To begin:
- Make sure you are logged in to the 123 Sheets website
- Click on the “Home” or “Taxpayers” link (top left), which ever one you see. If you clicked on “Taxpayers”, you’ll need to click on a taxpayer.
If you have not yet authorised the software, you will be prompted to do so. Click the green “Continue” button and follow the on-screen instructions. You will then be redirected to the HMRC website to log in to your Government Gateway account.
When logging in, make sure you use the Government Gateway account associated with your Self Assessment. Do not use another Government Gateway account that you may use for other taxes, as the authorisation will fail even though it may appear successful on the HMRC website.
On the HMRC website, you will be asked to authorise 123 Sheets to provide MTD for Income Tax services. Click the “Grant Authority” button, after which you will be redirected back to our website.
If the process is completed successfully, using the correct Government Gateway account, you will now have access to your MTD for Income Tax account through our software.
If Authorisation Fails
If the authorisation does not work, the screen will display a list of possible reasons why HMRC did not authorise the software. This list is provided by us to help guide you through common issues.
If you have checked all listed items and still cannot authorise the software, you will need to contact HMRC directly. As the authorisation process is controlled entirely by HMRC, we cannot see the reason for rejection and HMRC does not provide that information to us.
If you have forgotten or lost your self-assessment government login details, you can re-acquire these here: https://www.gov.uk/log-in-register-hmrc-online-services/problems-signing-in
You can check if you are logging in with the correct government gateway account, by logging in as normal to that government gateway account and looking for your NI. Number in there. If you cannot find it, you are in the wrong government gateway account.
If you need to contact HMRC, you can do so using the following options:
- MTD Helpline: 0300 322 9619
- Self-Assessment Helpline: 0300 200 3310 (ask to be transferred to MTD for Income Tax Support Team)
- International Self-Assessment Helpline: +44 161 931 9070
(Ask to be transferred to the MTD for Income Tax Support Team)
- Email: itsaenquiries.mtd@hmrc.gov.uk
Once the authorisation process has been completed successfully, you will be able to:
- Make MTD quarterly submissions
- View MTD data from your Income Tax account within our software
- File your tax return once the tax year has ended
Please note that all information displayed in 123 Sheets is live data retrieved directly from HMRC. We do not store any submitted figures, liabilities, or payment information relating to your tax account.
If what you see on our software from HMRC is not correct, you will need to contact HMRC, as we are only providing a “window” into what HMRC says about your tax affairs.