How to fill out a Self Assessment tax return
By Boring Money
7 Jan, 2025
If you're just starting out as a freelancer or self-employed, then the process of filling in and sending your Self Assessment tax return can be confusing and time-consuming. In this article, we run through the basics on filling out your own Self Assessment form, from the details you need to the deadlines you need to stick to, so you can be prepared for this year's paperwork!
What is a Self Assessment tax return?
A Self Assessment tax return is a form that many people in the UK have to fill out to enable HMRC (His Majesty's Revenue & Customs) to collect Income Tax.
Usually Income Tax is deducted automatically from your pension or wages if you’re on the PAYE system, but self-employed people, businesses and those with other sources of income must report it on a Self Assessment form so that the government is able to collect the appropriate amount of tax.
Making sure your form is correct and your details are up to date can prevent you from being charged too much tax – or too little. Filling out your own Self Assessment tax return also allows you to claim any tax allowances or relief you’re entitled to. You can send it to HMRC either on paper or online.
Who needs to complete a Self Assessment tax return?
You usually don’t have to submit a Self Assessment tax return if you’re an employee on the PAYE system unless you earn over £100,000 per year. However, the government website states that you need to file a tax return if, in the last tax year (6 April to 5 April), any of the following applied to you:
You were self-employed as a ‘sole trader’ and earned more than £1,000 (before taking off anything you can claim tax relief on)
You were a partner in a business partnership
You earned £100,000 or more
You paid High Income Child Benefit Charge
There are additional circumstances where you may need to complete a tax return, such as when you’ve received untaxed income from:
Some COVID-19 grant or support payments
Rental income
Tips and commission
Income from savings, investments and dividends
Foreign income
You can also submit a Self Assessment tax return to claim some Income Tax reliefs, make voluntary Class 2 National Insurance contributions to qualify for the State Pension or to demonstrate that you’re self-employed for benefits such as Tax-Free Childcare and Maternity Allowance.
Overall, there are numerous circumstances where you might need to fill in a Self Assessment tax return and it can be difficult to work out if you actually need to. For more information, head to the gov.uk website here.
What is the Self Assessment tax return deadline?
The deadline to submit your Self Assessment tax return differs depending on whether you’re doing so online or via post.
If you’re filing your Self Assessment tax return online
If you’re submitting your Self Assessment tax return online, you must do so by no later than midnight on 31 January. However, this is also the date that the payment itself is due -and of course, it is quite a job to work it all out - so it’s a good idea to submit it at least a few weeks before this.
It’s also worth noting that there are certain circumstances where you cannot file online, including:
For a partnership
For a trust or an estate
If you lived abroad as a non-resident
To report multiple ‘chargeable gains’, for example from life insurance
If you get income from a trust, you’re a Lloyd’s underwriter or a religious minister
If you’re sending your Self Assessment tax return by post
If you’re submitting via post, your Self Assessment tax return must be received by HMRC no later than midnight on 31 October (well before the January deadline for online submissions). However, as you can actually submit your tax return any time between the end of the tax year (5 April) and the respective deadline, it’s wise to complete paper tax returns as soon as you can so you don’t risk forgetting about it or rushing to sort out all your paperwork at the last minute!
How to register for Self Assessment
If it’s your first time sending a Self Assessment tax return, you’ll need to register online via the HMRC website. You will also need to register again if you did not submit a Self Assessment tax return last year, even if you have in previous years. The deadline for registration is 5 October (after the end of the tax year) and you could be fined if you do not do this in time.
There are different ways to register for Self Assessment depending on whether you’re self-employed, not self-employed but need to declare additional income, or if you’re in a partnership. You can start the process by going to the HMRC website here and clicking ‘self-employed’, ‘not self-employed' or ‘registering a partner or partnership’.
When you’ve registered, you’ll be sent a Unique Taxpayer Reference (UTR). You’ll need this for every Self Assessment tax return you submit so make sure you keep a note and don’t forget it!
What do you need to fill in a Self Assessment tax return?
If you’ve never filled in a Self Assessment tax return before, it can look daunting. But when you understand the process, it’s actually quite straightforward – as long as you have all the information you need! Otherwise, you could be scrambling around looking for paperwork on the tax you owe before the deadline.
Before you start, make sure you have:
Remember that you can actually submit your Self Assessment tax return any time between the end of the tax year and the deadline, so it’s a good idea to get into a habit of collating the above paperwork nice and early so you have plenty of time and can identify if there’s anything missing well before 31 January.
How to send a Self Assessment tax return
How you send your Self Assessment tax return depends on whether you’re submitting it online or via post.
File your Self Assessment tax return online
To submit your tax return online, you’ll need to make sure you’ve already registered with HMRC (you can do so here) by 5 October at the latest. Remember that missing the registration deadline can mean you’ll receive a fine.
To start filling out your Self Assessment tax return online, you’ll need to sign in using your Government Gateway user ID and password and you’ll also need to have your UTR number to hand. You will then be logged into the portal where you can begin your submission.
The good news is that you don’t have to complete it all in one go. You can save your entry, log out and come back to it at a later date if you need to. Just remember not to miss the final 31 January deadline for online submissions!
Send your Self Assessment tax return by post
If you’re submitting your Self Assessment tax return by mail, you’ll also need to make sure you’ve registered with HMRC (click here) by no later than 5 October. However, the deadline to complete your form if you’re sending via post is much earlier – 31 October – so bear this in mind.
As you can submit your entry any time after the end of the previous tax year (5 April) and the deadline (in this case, 31 October), it makes sense to get ahead and start the process as soon as possible.
In order to get a paper copy of the Self Assessment form, you’ll need to call HMRC and request form SA100. The telephone details are as follows:
Telephone: 0300 200 3610
Outside UK: +44 161 930 8331
Opening times: Monday to Friday, 8am to 6pm (closed on Saturdays, Sundays and bank holidays)
Once you’ve got the SA100 form and completed your Self Assessment, the address you’ll need to post your tax return to is:
Self Assessment
HM Revenue and Customs
BX9 1AS
United Kingdom
What if you can’t pay your tax bill?
If you can’t afford to pay your tax bill, there are options available to you – but it’s crucial that you contact HMRC as soon as possible to prevent being fined. If you don’t pay on time, you might have to pay interest on the outstanding bill and penalty charges.
You can contact HMRC's digital assistant for help with payment problems - use this link. HMRC will then look at how much you owe as well as factors such as your income and expenditure to decide if they will give you more time to pay your tax. This could be an extended deadline or a chance to submit the payment in instalments.
Tax is a high priority form of debt due to the interest and penalty charges you have to pay for late payments. However, if you’re struggling to pay it or you’re worried about other debt, there are lots of resources available to you for help, support and guidance on how to get back on track. You may find the following charities useful if you feel that you're struggling:
Samaritans
A free, 24/7 telephone service for anyone suffering from emotional distress or contemplating suicide
Telephone: 116 123 (Monday to Sunday at any time)
Welsh Language Line: 0808 164 0123 (Monday to Sunday, 7pm to 11pm)
Shout
A free, confidential, 24/7 text messaging service for anyone who is struggling with their mental health
Text 'SHOUT' to 85258 to start a conversation with a trained Shout volunteer
Texts are free, anonymous and confidential from anywhere in the UK
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