Deadlines and admin
Filing a self-employed Self Assessment tax return
Most of the work happens before you sign in: once the figures are ready, the return itself is a matter of copying them across.
A sole trader with £26,000 of profit and an £18,000 salary taxed through PAYE ends up, after the return is filed, with a balance of £6,006 to pay: Income Tax on all £44,000 of income comes to £6,286, Class 4 to £806, and the £1,086 already deducted by the employer is taken off. That is the logic of every Self Assessment return. You report what you earned from each source, HMRC’s system works out the tax on the total, subtracts anything already paid, and the result is either a bill or a repayment. For the 2025/26 year the online return and the money are both due by 31 January 2027. The calculation that comes back is the SA302. Enter your own turnover, expenses and P60 figures below to see what yours is likely to show.
What your tax calculation will show
Balance to pay
£6,006
| Income Tax on all income | £6,286 |
| Class 4 | £806 |
| Less tax already deducted | £1,086 |
Before payments on account and any student loan.
Figures checked by Radif Partners · Editorial policy · How we calculate
What to gather before you sign in
A return goes faster when every figure is on one sheet before you open the form. For a sole trader that sheet has three parts.
The business figures
Turnover for the year: everything invoiced or, under the cash basis, everything received. Then allowable expenses, grouped the way the form groups them: stock and materials, travel, premises, phone and stationery, insurance and so on (GOV.UK, expenses if you’re self-employed). If you use simplified expenses for mileage or working from home, have the miles and the hours ready. If your gross income is small, compare your real expenses with the £1,000 trading allowance: a market stall with £2,400 of takings and £1,900 of costs is taxed on £500 using its expenses, because that gives the lower profit.
Income from elsewhere
Your P60 for any job (pay and tax deducted), untaxed savings interest, dividends, rent, and anything else HMRC does not already tax at source. The return covers all your income, not only the business, which is why a salary changes the tax on the profit.
Reliefs and loans
Personal pension contributions paid under relief at source, which can bring extra relief at the higher rates, and your student loan plan if you have one: repayments on self-employed income are collected through the return, and they are added to the bill rather than reducing it.
Finally, the practical items: your Unique Taxpayer Reference, your sign-in details, and your bank details for a possible repayment. First-time filers must have registered for Self Assessment first, by 5 October after the end of the tax year (GOV.UK, how to register).
Which year, and which accounts
The return for 2025/26 covers the tax year that ended on 5 April 2026. GOV.UK points out that records kept to the same 6 April to 5 April dates make the return simpler. Since 2024/25 the cash basis is the default: income counts when the money arrives and costs when you pay them, so an invoice sent in March but paid in May belongs to the next year (GOV.UK, cash basis). If you opted out for traditional accounting, add what customers owed you at the year end and the bills you had received but not paid, plus stock and work in progress.
A business whose accounts end on another date has profit to allocate between tax years. If the final number is not ready by the deadline, GOV.UK allows provisional figures, flagged as such, with an amended return once the accounts are done.
The filing itself, step by step
- Sign in to HMRC online services with your sign-in details and UTR. You may be asked to prove your identity, usually with photo ID such as a passport or driving licence.
- Work through the sections that apply to you: self-employment, employment, property and so on.
- Fill in the self-employment page with turnover and expenses, or with the trading allowance in place of expenses.
- Add the employment page from your P60, then any other income, reliefs and the student loan plan.
- View the calculation before you submit and save a copy, since after filing it can take up to 72 hours to show.
- Submit the return, then pay what the statement shows by 31 January.
You do not have to finish in one sitting; the online return can be saved and picked up later. It can be filed any day after 5 April, and doing it early gives you the figure months before the payment is due.
Reading the SA302 calculation
The SA302 sets out your total income on which tax is due, the allowances and reliefs given against it, how HMRC worked out the tax, and the total you owe for the year. It deliberately ignores what you have already paid towards that year through payments on account or a budget plan, and any older debt. Those appear on the Self Assessment statement, which is the document that tells you what to pay (GOV.UK, understand your Self Assessment bill). A copy can be printed from your online account, and GOV.UK explains how to get an official one, for example for a mortgage application.
SA302: what the year costs. Statement: what you still owe after payments already made. Payments on account: the advance on next year, added to the statement, not to the SA302.
When the result is a bill
Take the example from the top of the page: an £18,000 salary with £1,086 of tax deducted through PAYE, and £26,000 of profit from a weekend photography business. Tax on the combined income is £6,286, Class 4 on the profit is £806, so £6,006 remains to pay. Because less than 80 % of the total was taken at source and the balance is over £1,000, HMRC also sets payments on account of £3,003 each. In the first year, 31 January therefore brings the balance plus the first of those. For a sole trader with no job and £38,000 of steady profit, the second year looks calmer: two payments on account of £3,306 cover a bill of £6,612, and nothing extra is due in January apart from the next instalment. The payments on account page has the detail.
When the result is a repayment
A repayment appears when more was taken at source than the year’s liability, or when payments on account were set from a better year than this one. Picture someone with £24,000 of wages and a small online shop that made £500: the liability is £2,386 of Income Tax and £0 of Class 4, so if the P60 shows more than £2,386 deducted, the calculation ends with money owed back. HMRC pays it to the bank account on the return, unless a payment such as a payment on account falls due within the next 45 days, in which case it can be set against that instead.
Paper returns and the cases online filing cannot handle
The paper SA100 still exists, but it must arrive by 31 October 2026 for 2025/26, three months before the online date (GOV.UK, Self Assessment deadlines). HMRC’s own online service does not take partnership returns, trust or estate returns, returns for non-residents, or a few specialist cases such as Lloyd’s underwriters and ministers of religion; those go through commercial software or paper forms. An ordinary sole trader with no such complications can use HMRC’s online service.
After filing
Mistakes can be corrected within twelve months of the filing deadline, online after a 72-hour wait or on paper with each page marked as an amendment. The updated statement shows whether you owe more or are due money back, and any change to your payments on account. Keep the records behind the return for at least five years after the January deadline. Anyone already in Making Tax Digital still files a final return by the same January date, built on the quarterly updates sent during the year; the Making Tax Digital checker shows whether that applies to you. For a full estimate including student loans, use the Self Assessment calculator.