Self Assessment Quick Links:
Do I need to Submit a Self Assessment?
Step 1: Organize Self Assessment Documents
Step 2: Register for Your Self Assessment
If you’re a UK resident, you will know that the deadline for Self Assessments is around the corner. This might seem daunting to many, but it’s okay. We’re here to help you through it, step by step!
Do I Need to Complete A Self Assessment?
Many individuals in the UK need to submit a self-assessment.
If you are employed by a company and pay tax at source (i.e. your company is doing your PAYE – Pay As You Earn monthly), you do not need to submit a self-assessment UNLESS you earn over £150,000 annually.
If you are earning an income which you have not paid tax on, you need to complete a self-assessment. This includes, but is not limited to:
- Your Taxable income was OVER £150 000
- You received a P800 from HMRC saying you didn’t pay enough tax last year
- Sole Proprietor income over £1000.00
- Rental income of over £2500.00
- Untaxed income (like tips or commission) over £2500.00
- Savings or Investment Income over £10,000
- Income from selling shares or second homes
- You’re a director of a company
- Claiming child benefit and your (or your partner’s) income exceeds £50 000.00
- Earning international income, or reside outside of the UK, but earning in the UK
- You’re a trustee of a trust or registered pension scheme
- Your State Pension was your only source of income and was more than your personal allowance (£12,570)
Now that you know whether or not this is something you should be doing. Let’s take you through the steps to complete your Self-Assessment online:
Pre-planning prevents failure, right? So ensure that you are logging in with all the necessary documentation already compiled so you don’t have to scramble around trying to collect documents and information while you are attempting to submit everything.
What will you need for your Self-Assessment?
You will need the following documents and information to complete your online self-assessment:
- Your ten-digit Unique Taxpayer Reference (UTR)
- Your National Insurance number
- Details of your untaxed income from the tax year (including income from self-employment, dividends and interest on shares)
- Records of any expenses relating to self-employment.
- Any contributions to charity or pensions that might be eligible for tax relief (If applicable)
P60 or other records showing how much income you received that you’ve already paid tax on (via PAYE).
Step 2 - Register for Your Self-Assessment
If this is your first time doing a self-assessment, you will have to register for self-assessment on the GOV.uk.
There are three categories of registration.
If you are a sole proprietor and earning an income over £1000, you are required to registered for self assessment.
Step 3 - Fill In The Online Self-Assessment Form
There are two sections in the self-assessment form. The first section (main section) deals with:
- Income (taxed and untaxed) in the form of dividends and interest.
- Contributions to your Pension Fund
- Donations made to charity.
- Benefits (State Pension, Child Benefit and Blind Person’s Allowance).
The second section of the Self-Assessments mainly deals with any additional income that you have from being self-employed (SA103), property income (SA105) or declaring capital gains (SA108).
Remember that when you are filing as a self-employed individual, you can also claim tax relief. If your annual turnover is under £85,000 you can enter the lump sum of your total expenses without categorising or itemise your expenses. However, if your turnover is over £85,000 you are required to categorise each expense including a total at the bottom. These expenses can include:
- Office costs, for example stationery or phone bills
- Travel costs, for example fuel, parking, train or bus fares
- Clothing expenses, for example uniforms
- Staff costs, for example salaries or subcontractor costs
- Things you buy to sell on, for example stock or raw materials
- Financial costs, for example insurance or bank charges
- Costs of your business premises, for example heating, lighting, business rates and maintenance
- Advertising or marketing, for example website costs
- Training courses related to your business, for example refresher courses
- Interest on loans
- Bank, credit card and other financial charges
- Accountancy, legal and other professional costs.
- Vehicle and travel expenses
If you are claiming expenses it is important for you to keep a detailed record of all your expenses for up to 5 years.
Step 4 - Pay Your Self Assessment
When you’ve successfully submitted your self assessment, HMRC will notify you what your bill is (tax and national insurance if applicable). You can pay in whatever way is most comfortable for you. Some of the options available are:
- Online Banking.
- CHAPS (Clearing House Automated Payment System).
- Corporate Credit Card.
- Debit Card.
- At your Local Bank.
- At your local building society.
- Send a cheque.
- Arrange Bank Transfer.
- Direct Debit.
However, it is essential to note the deadline (31 January). HMRC must have received the payment by the deadline. If you’re paying on the deadline or very close to it, it is recommended that you use instant payment methods to avoid penalties.
If you’re close to or past the 31 January deadline, filing late can trigger automatic penalties. We explain how these work and how to limit exposure in our guide to handling late filing penalties from HMRC.
If you’re having trouble with your self assessment you can reach out to the CIGMA Accounting team.
Frequently Asked Questions
How do you do a self assessment tax return in the UK?
To do a self assessment, you register with HMRC, gather your income and expense records, complete the online tax return, and submit it before the deadline. You then calculate and pay any tax owed based on your total taxable income.
What are the main steps in completing a self assessment?
The main steps include registering for self assessment, collecting financial records, completing the SA100 form, calculating tax due, and submitting the return online. Accurate bookkeeping throughout the year makes the process much easier.
What self-assessment advice should UK taxpayers follow in 2026?
In 2026, key self-assessment advice includes keeping digital records, tracking all income sources, claiming all allowable expenses, and submitting returns early. This helps reduce errors and avoid HMRC penalties.
Who needs to complete a self assessment tax return?
You must complete a self assessment if you are self-employed, a landlord, a company director receiving dividends, or have untaxed income above HMRC thresholds. It ensures all income is properly reported and taxed.
What happens if you miss the self assessment deadline?
Missing the deadline results in automatic penalties, starting with a fixed fine and increasing over time. Interest is also charged on unpaid tax, making timely submission essential to avoid unnecessary costs.
How can you make self assessment easier and more accurate?
You can simplify self assessment by using accounting software, maintaining monthly records, separating business and personal finances, and seeking professional advice where needed. This reduces stress and improves accuracy.
Simplify Your Self Assessment and Reduce HMRC Filing Errors
Accurate self assessment accounting is essential for HMRC compliance. We help UK taxpayers understand how to do a self assessment, provide practical self-assessment advice, and ensure correct reporting to reduce errors and improve filing accuracy.
Trusted guidance from London-based accountants, focused on accuracy, clarity, and compliance.
