Female entrepreneur in blue shirt drinking coffee at desk in front of laptop

How to fill in your Self Assessment tax return

January 6, 2023
Self Assessment season is once again upon us, and with Making Tax Digital for Income Tax delayed until 2026, business owners can expect to continue filing their tax returns annually for another few years to come.Whether you’ve recently launched your first small business or plan on setting up a side hustle, you might be wondering whether you need to file a Self Assessment — and if so, how to fill one out.If so, you’re in the right place. We’ll be outlining what exactly a Self Assessment form is, who needs to fill one out, and a step-by-step guide to take to successfully submit your Self Assessment.

What is a Self Assessment tax return?

Simply put, a Self Assessment is HM Revenue and Customs (HMRC)’s way of collecting Income Tax and National Insurance contributions (NICs) from sole traders, limited company directors and taxpayers under exceptional circumstances (we outline what some of these are below).
The majority of employees pay their taxes through PAYE, otherwise known by its full moniker as Pay As You Earn. This system is a way for HMRC to collect Income Tax and National Insurance from employees at source, deducted from their salaries whenever their employer runs payroll.

For the taxpayers who aren’t on PAYE (notably, self-employed sole traders), they’ll need to file a tax return to HMRC, declaring their income and business expenses from the relevant tax year. From the information submitted, HMRC can then calculate how much tax they owe, and whether they’re eligible for any tax breaks or benefits.

Who needs to file a Self Assessment?

If you’re a small business owner, you’ll need to file a Self Assessment if you’re:
    A self-employed sole trader earning more than £1,000 (before expenses)A partner in a business partnershipRenting out property as a landlord
You’ll also need to file a Self Assessment tax return if:
    Your self-employment income was more than £1,000 before claiming allowable expenses Your income from renting out property was more than £2,500 (you’ll need to contact HMRC if it was between £1,000 and £2,500) You earned more than £2,500 in untaxed income from tips or commission Your income from savings or investments was £10,000 or more before tax You need to pay Capital Gains Tax on profits from selling things such as shares or a second home You’re a company director (excluding directors of non-profit organisations, such as charities) You or your partner’s income was above £50,000 and you’re claiming Child Benefit You have income from abroad that you need to pay tax on You live abroad, but generate income from self-employment or rental property in the UK You’re a trustee of a trust or registered pension scheme State Pension was your only source of income and was more than your Personal Allowance You received a P800 from HMRC saying you didn’t pay enough last tax year Your taxable income was above £100,000 — even if you’re an employed individual on PAYE You want to make voluntary Class 2 National Insurance contributions to qualify for certain benefits, such as the State Pension)
Not sure if you need to file a Self Assessment? HMRC has a tool you can use to check whether you need to send one off.

How do I register for Self Assessment?

If you need to file a Self Assessment, you’ll first need to register for Self Assessment with HMRC. You can either do this online or by post, although we strongly recommend doing this online.
If you opt to file by post, you’ll need to fill out this form online before printing off and sending to HMRC. However, if you want to avoid the risk of your submission getting lost or delayed in the post, you may benefit from registering for Self Assessment online.

To register online, you’ll need to take the following steps:
    Sign into your Government Gateway account and add ‘Self Assessment’. After doing this, you’ll get your Unique Taxpayer Reference (UTR) number in the post within 10 days, or 21 days if you’re abroad. You’ll be sent an activation code in the post to access HMRC’s online services. From there, you can file and submit your Self Assessment.
Keep in mind that if you’re filing your Self Assessment for the first time, you’ll need to register by 5th October of the relevant tax year. Not sure how to register? Get in touch with one of our Self Assessment experts today.

How to fill in your Self Assessment

Gather the information you need

Before you can fill in your Self Assessment, you’ll need to make sure you’ve got the following information close to hand:
    Your 10-digit Unique Taxpayer Reference number National Insurance number Details of your untaxed income from the tax year, such as income from self-employment, dividends and interest on shares Records of any expenses relating to self-employment Any contributions to charity or pensions that may be eligible for tax relief A P60, or any other records that show how much income you’ve received that you’ve already paid tax on

Fill in the sections that apply to you

One thing about the Self Assessment: there’s a lot of paperwork. The good news is that you don’t need to fill out all of it — just those bits that apply to you.There are 2 parts to a Self Assessment return, with the main section being the SA100. This part of the return deals with taxed and untaxed income, pension contributions, charity donations, and certain state benefits.To help you understand what needs to go in each section, we’ve summarised each section in the table below:
SectionDescription
Income
    Declaring tax and untaxed income from interest earnedDividends from shares
Pensions, annuities and benefitsIf you're retired, enter the:
    Total amount of State Pensions you were entitled toGross amount of any State Pension lump sumGross amount of annuities or pension lump sums (aside from State Pension
Other UK incomeOther taxable income that isn't related to interests, dividends or anything else on the supplementary pages (scroll down for more). You can also use this section to enter any allowable expenses related to this income, and any Income Tax already paid on them.
Pension contributionsPayments made into a registered pension scheme, annuity contract or employer's scheme
Charity donationsGift Aid donation totals, as well as shares, securities, land or buildings gifting to charity
Blind Person's AllowanceState if you're claiming this allowance
Student loan repaymentsState if you're currently making Student Loan repayments, alongside any deductions made by your employer
High income Child Benefit chargeOnly fill in this section if you're receiving Child Benefit and your income was above £50,000 in the relevant tax year
Marriage AllowanceIf your income for the tax year was less than the Personal Allowance, you can use this section to state that you want to transfer some of your Personal Allowance to your spouse
If you have extra income to declare from self-employment, property or Capital Gains, you’ll need to complete a supplementary page.In these pages, you’ll need to report any untaxed income you have from these sources, and any allowable expenses, which will be deducted from your final bill.For every stream of income you have, you’ll need to fill out its associated page.SA103: Self-employment
SectionDescription
IncomeAnnual business turnover before deducting expenses. If you have more than one source of self-employment income, you can enter this amount separately.
Self-employment income support grant (SEISS)You'll need to declare any grants you've received from SEISS under 'Other tax adjustments for your business trading name'
ExpensesExpenses to include:
    Cost of stock purchased for resale Cost of equipment Staff costs, including wages, salaries, and payments to subcontractors if you're in the construction industry Rent, power and insurance Office costs, including WiFi, mobile phones and stationery Vehicle and travel expenses Marketing and advertising costs Interest on loans Bank, credit card and other financial charges Accountancy, legal and other professional costs Training materials and subscription costs
Keep in mind that you won't need to send in proof of your expenses, but will need to hang on to your records for 5 years after you submit your Self Assessment return for the relevant tax year in case of an audit.SA105: UK property income
SectionDescription
IncomeIncome received from rented properties. This is divided into two sections, with the first being dedicated to income from properties in the UK, and the second dedicated to the total rent and income from other properties.
ExpensesYou can claim for:
    Rates, insurance and ground rent Property, repairs and maintenance Loan interest and other financial costs Legal, management and other professional fees
SA108: Capital Gains
SectionDescription
IncomeIncome declared for Capital Gains Tax is called 'disposal proceeds', and includes:
    Residential propertyNon-residential propertyShares and securities
ExpensesYou can claim for 'allowable costs', such as:
    Price of purchasing the asset initiallyCosts of any improvements when soldOther costs in buying or selling the asset (e.g. Stamp Duty)

Submit your Self Assessment tax return

After you’ve filled out your Self Assessment, you’re then free to file your return to HMRC. However, you’ll need to make sure you get your return in before the Self Assessment deadlines, or you could face some late filing fines.If you’re opting to file a paper tax return, you’ll need to make sure your return is at HMRC’s offices by midnight 31st October after the end of the tax year, so aim to send your tax return form a few days beforehand to make sure it gets there on time. As for those filing an online tax return, the deadline is midnight 31st January.Instead of worrying about your Self Assessment this year, let Ember take care of it for you. For £99+VAT, we’ll draft and file your Self Assessment for you, without any hassle.

Join us in creating the new age of accounting.

Simple language, simple software, so that you can spend less time dealing with admin and more time focusing on what really matters.