A Plain Guide to Self Assessment for Freelancers
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If you earn money freelancing in the UK, self assessment is how HMRC collects income tax and National Insurance on what you earn. This guide covers registration, deadlines, allowable expenses and what to do if you have already missed something.
Why self assessment matters for freelancers
When you are employed, your employer deducts income tax and National Insurance before you are paid. When you freelance, nobody does that for you. HMRC requires you to report your own income and pay whatever tax is owed through a self assessment tax return.
You must register if your self-employment income exceeds £1,000 in a tax year. The tax year runs from 6 April to 5 April, and registration must be completed by 5 October following the end of the tax year in which you started freelancing. Miss that date and you are already behind.
From April 2026, sole traders with qualifying income above £50,000 in the 2024/25 tax year must use Making Tax Digital for Income Tax instead of the standard online return. From April 2027 the threshold drops to £30,000, and from April 2028 to £20,000. HMRC may write to you if you are affected, but you are responsible for checking regardless of whether you receive a letter. Full details at GOV.UK: Making Tax Digital for Income Tax.
Where most freelancers go wrong
The majority of problems I see come down to three things: registering late, claiming expenses incorrectly and misunderstanding the payment schedule. None of these are difficult to fix once you know about them, but they each carry a cost if you ignore them.
Missing the registration and filing deadlines
HMRC charges a £100 penalty the moment a return is one day late. After that, £10 per day is added for up to 90 days, taking the running total to a possible £1,000 before any unpaid tax is considered. At six months, a further charge of 5% of the tax owed or £300 (whichever is greater) is applied, and the same again at twelve months. Late payment also carries its own separate charge: 5% of unpaid tax at 30 days, six months and twelve months, with interest on top. Full penalty rates are published at GOV.UK: Self Assessment penalties.
Claiming the wrong expenses
HMRC only allows expenses that are wholly and exclusively for business use. If you use your phone for both personal and work calls, only the business proportion is deductible. Common categories include office costs, travel, software and professional subscriptions, but each claim needs to be justifiable with a receipt or record. A full list of allowable costs is at GOV.UK: Expenses if you are self-employed.
“Most of the freelancers I work with come to me after a year of doing it themselves. The return got filed, but they had overclaimed on one thing, underclaimed on another, and had no idea payments on account were coming in July. Getting it right the first time is always cheaper.”
What to do, step by step
The process has a fixed order. Work through it in sequence and you will not miss anything critical.
- Register for self assessment via your Government Gateway account at GOV.UK. You need a National Insurance number and a form of ID. Do this by 5 October following the end of the tax year in which your freelance income started. If you already have a Gateway account from a previous employment, use the same login.
- Gather your records for the tax year. You need total income received, a list of allowable business expenses with supporting receipts, any employment income shown on a P60 if you also worked a PAYE job, and details of any other taxable income such as interest or rental income. The more organised these records are before you sit down to file, the quicker the return takes.
- Complete and submit the return by the deadlines. Paper returns must be filed by 31 October. Online returns must be submitted by 31 January following the end of the tax year. Any tax owed is also due by 31 January. If your bill exceeds £1,000, HMRC will ask for payments on account toward the following year on 31 January and 31 July.
If you have been freelancing for more than a year and have not yet registered, register now. HMRC can accept late registrations and late returns together. The penalties for not registering at all are greater than those for a late return, so acting promptly reduces the overall cost.
Costs and what to expect
Whether you file yourself or use an accountant depends on how straightforward your income is. A single source of freelance income, simple expenses and no other complications can often be managed with a few hours of focused work. Multiple income streams, limited company involvement, CIS deductions, VAT or missed prior years add layers that most freelancers find genuinely hard to handle without guidance.
| Option | Pros | Cons |
|---|---|---|
| DIY via HMRC online | No accountant fee. You control the timeline. | Higher risk of missed expenses or incorrect figures. No one to catch errors before submission. |
| Using an accountant | Accurate filing, expenses reviewed properly, penalties less likely, someone to answer questions. | An annual or monthly fee applies. Worth comparing against the tax saving and time cost of doing it yourself. |
How to get started today
If you are unsure where you stand, start with the registration question. If you earned more than £1,000 from freelancing in any UK tax year since 2017/18 and have not yet filed a self assessment return, you need to act. HMRC has a process for late registrations and will work out any penalties at that stage. Doing nothing always costs more than doing something late.
- Check whether you are already registered by logging into your Government Gateway account at GOV.UK. If you have never registered, do so before the 5 October deadline for the current tax year.
- Start keeping a clear record of income and expenses now, even if the filing date is months away. A simple spreadsheet showing date, amount and category is enough to start. Cloud accounting tools such as QuickBooks or FreeAgent make this faster if you invoice regularly.
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