How to complete your Self Assessment tax return

8 Nov 2022

If you’re new to self-employment, the prospect of filling in a self-assessment tax return can seem daunting. The good news is there are lots of supporting documents out there to guide you through the process, and if in doubt, you can always contact HMRC. Here’s how to complete your tax return on time to avoid any late filing fees.

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When do I need to complete my tax return?

UK tax returns are for tax years not calendar years. The tax year starts on 6 April and finishes on 5 April the following year. Tax returns are submitted in arrears. 

If you’re filing a paper tax return for the 2021/22 tax year, you need to do this by midnight on 31 October 2022. If you’re filing online, you have until midnight on 31 January 2023 to submit. Whether you’ve chosen paper or digital, you’ll need to pay HMRC the tax you owe by midnight on 31 January 2023, or risk incurring a penalty fee.

If this is your first time submitting a return, the deadline for registering for Self Assessment was 5 October 2022. If you no longer need to submit Self Assessment tax returns, you’ll need to contact HMRC to let them know. 

How to register for online Self Assessment

  • Step 1:Register for Self Assessment on the HMRC website.

  • Step 2: Once you’ve set up your user ID and password, HMRC will send your 10-digit Unique Taxpayer Reference (UTR) through the post.

  • Step 3: HMRC will also send you an activation code that will enable you to file your tax return online. This can take up to seven days, so register well in advance of the deadline. 

  • Step 4: Activate your account within 28 days of the date on your activation code letter (otherwise you’ll have to request a new one).

Here’s what you’ll need in order to complete your Self Assessment tax return:

  • Your Unique Taxpayer Reference (UTR)

  • Your National Insurance number

  • Details of untaxed income for the tax year

  • Details of any self-employment expenses

  • P60 for any income that you’ve already paid tax on

 If you need help, this page is very useful and can signpost you to the right place. The website also contains details of the ways in which you can get in touch with HMRC, as well as links to the Self Assessment tax return form itself. 

Completing your Self Assessment tax return online

You only need to fill out the sections of the Self Assessment tax return that are relevant to your circumstances. You don’t have to do it all in one go either: you can save it and go back to it when you have more time or have found the relevant information. 

Once you’ve filed your return online, you’ll get an on-screen notification telling you that HMRC has received it, as well as a reference number. It’s worth taking a screenshot or noting this reference number down in case you need to prove that you filed your return. 

If you’re submitting a Self Assessment tax return through the post, you’ll need to understand which supplementary pages you may have to complete alongside the SA100 form. You won’t receive a notification from HMRC when they receive it, so it’s recommended that you send it ‘tracked’. 

Some people might be sent a simplified SA200 return to submit. This isn’t something you can choose to do – HMRC will send it to you if you’re eligible. Whether you’re completing the standard or simplified version, remember to check that your personal details are correct before you submit.  Here are the things you may be asked to include: 

Income & expenses

Details of taxed and untaxed income from self-employment. You may also be required to provide details of taxable interest on savings, together with capital gains from asset sales and shares dividends. You can also provide details of any allowable expenses.


You might be required to detail the total amount of state pensions you were entitled to and any lump sums, as well as any annuities or lump sums relating to private pensions. 


Benefits include things like Jobseeker’s Allowance and Carers Allowance. Other information required may include: 

  • Charitable donations

  • Blind Person’s Allowance

  • Student loan repayments

  • High income child benefit 

  • Marriage allowance

If you fail to meet the deadline for filing your tax return (31 October for paper, 31 January for online), you could automatically be charged £100. You may also be charged if you fail to pay the tax you owe on time. 

If you’re struggling to pay your tax bill, get in touch with HMRC via the Payment Helpline on 0300 200 3825. Lines are open Monday to Friday, from 8am to 6pm.

Stuart Lawson

Chief Commercial Officer

Stuart is Chief Commercial Officer at Funding Options where he plays a key role in driving the growth of the business and its relationships with more than 120 partners. A finance industry veteran, he has a strong background in alternative finance, corporate and commercial banking, as well as global transaction banking.

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