Lesson 3 – Self Assessment Process

Southwark Pioneers Fund: Launchpad

When to file SELF-ASSESSMENT TAX RETURN ?

The self-assessment return needs to be completed when you have income over £1,000 in a tax year that is taxable and hasn’t been taxed automatically (at source, through PAYE).
The tax year runs from 6th April one year to 5th April the next.
If this is applicable to you then you will need to register for self-assessment.

In this section, we will look at how to complete your self-assessment and file your online tax return on HMRC website.

REGISTRATING FOR SELF-ASSESSMENT

To register:

Go to HMRC website, you only need to do this the first time. Complete your Online Registration for your first Self-assessment https://www.gov.uk/register-for-self-assessment
You will need to have some information at hand when you register; these include your personal details and your national insurance number.
You then choose what type of registration you are doing, either self-employed or partnership for instance.
You let HMRC know when this income started and what type of work you are doing.

WHAT AFTER REGISTRATION OF SELF-ASSESSMENT ?

Once registered,

You will receive a letter from HMRC which will have your Unique Tax Reference (UTR) number on it.
Once you have the UTR you can then set up a government gateway account. Setting this up means you can use this to submit your self-assessment return online.
There are instructions on the UTR letter to let you know how to do this. You will need some documents to be able to set this up like your passport or driving licence, perhaps a recent payslip or P60. To verify.
Once you have followed instructions from previous slide, you then must wait to receive an activation code in the post from HMRC.
Once received, log in to your government gateway account; this is now set up ready to complete your return. This can take some time to get all the things set up that you need, HMRC does say this might take 15+ working days to get things in place.
It is always best to make sure you can access your government gateway account before you complete your return if there is some reason you cannot log in, then you have time to resolve the issue.

There are deadlines to submit your return. For 2025/2026 you need to register for self-assessment before 5th October 2026 if you have never submitted a return before.

If you are filing your return for 2024/25 on paper, you need to file it before 31st October 2025.
If you are filing online, you need to submit your return before 31st January 2026 for year 2024/25.
You may be charged a penalty if you fail to meet any of these deadlines.
You can proceed to submitting your self-assessment return to HMRC using the government gateway.

When to pay your tax bill?

Tax is due by the 31st January following the tax year for the tax return year ended.

For Example: Tax years run from 6th April one year to 5th April the following year. For the tax year ended 5th April 2026, the tax would be payable by 31st January 2027.

Things get a bit more complicated, if your tax bill is more than £1,000 then you would need to also make payments on account in the 31st January and second payment on 31st July, paying towards the following years tax bill.