The Self Assessment return for the 2025/26 tax year must be filed online by 31 January 2027, with the tax paid the same day; paper returns are due by 31 October 2026 and anyone filing for the first time must register by 5 October 2026. Where the previous year’s bill was over £1,000 and less than 80% of it was collected at source, two payments on account of half that bill each fall due on 31 January and 31 July. A sole trader with £30,000 of profit owes £4,531.80 for the year and, in their first January, pays £6,797.70. Missing the filing date costs £100 immediately and considerably more after three months.
The calendar during 2026/27
| Date | What is due |
|---|---|
| 31 July 2026 | Second payment on account for 2025/26 |
| 5 October 2026 | Deadline to register for Self Assessment if you had untaxed income in 2025/26 for the first time |
| 31 October 2026 | Paper return for 2025/26 |
| 30 December 2026 | Online return for 2025/26 if you want tax under £3,000 collected through your PAYE code |
| 31 January 2027 | Online return for 2025/26, balancing payment for 2025/26 and first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
| 31 January 2028 | Return and balancing payment for 2026/27 |
Registration, filing and payment can all be done online through the personal tax account, and the return can be filed any time from 6 April after the tax year ends. Filing early does not bring the payment date forward; the tax remains due on 31 January, but an early return gives an accurate figure for the payments on account and time to set money aside. The Self Assessment calculator estimates the bill from profit before the return is prepared.
Who has to file
Anyone with self-employment income above the £1,000 trading allowance, partners in a business, landlords with rental income above £2,500 after expenses or £10,000 before, people with untaxed income such as savings and investment income over £10,000, and anyone with a capital gain to report. Employees taxed only through PAYE do not normally need to file, although a claim for expenses or the High Income Child Benefit Charge can bring them in unless the charge is collected through the tax code. Company directors are not required to file simply for being directors, but dividends over £10,000 make a return necessary. The side hustle tax calculator shows whether trading income on top of a job crosses the allowance and what it costs.
Payments on account
| Profit for 2025/26 | Tax and Class 4 NI for the year | Payments on account for 2026/27 | Paid on 31 January 2027 | Paid on 31 July 2027 |
|---|---|---|---|---|
| £15,000 | £631.80 | none, bill under £1,000 | £631.80 | £0 |
| £30,000 | £4,531.80 | £2,265.90 each | £6,797.70 | £2,265.90 |
| £50,000 | £9,731.80 | £4,865.90 each | £14,597.70 | £4,865.90 |
| £80,000 | £22,288.60 | £11,144.30 each | £33,432.90 | £11,144.30 |
The January figure in the first year of Self Assessment is the whole of the previous year’s bill plus half of it again in advance, which is the payment most new sole traders are unprepared for. Thereafter each January carries the balancing payment, being the actual bill less the two payments on account already made, plus the first payment on account for the following year. Payments on account can be reduced online where profit is expected to fall, but interest is charged if the reduction proves too large. The payments on account calculator sets out the sequence for any profit, and the tax set aside calculator gives a percentage of each invoice to put away so the January bill is covered.
What the bill contains
For a sole trader the bill is income tax on profit above the £12,570 personal allowance plus Class 4 National Insurance at 6% on profit between £12,570 and £50,270 and 2% above. Class 2 National Insurance is no longer charged, but a self-employed person with profit of at least £7,105 receives a National Insurance credit for the year, and one with lower profit can pay Class 2 voluntarily at £3.65 a week to protect their State Pension record. Dividends, savings interest, rental profit and capital gains are added on their own rates; our guides to dividend tax and capital gains tax cover those, and the VAT threshold guide explains the separate registration test for turnover above £90,000.
Penalties and interest
| Failure | Penalty |
|---|---|
| Return up to 3 months late | £100, even if no tax is due |
| More than 3 months late | £10 a day for up to 90 days, maximum £900 |
| More than 6 months late | 5% of the tax due or £300, whichever is greater |
| More than 12 months late | A further 5% or £300, whichever is greater |
| Tax paid late | 5% of the unpaid tax at 30 days, again at 6 months and again at 12 months |
Interest runs on late tax from the due date at HMRC’s late payment rate, 7.75% a year at the time of writing, and applies to payments on account as well as balancing payments. Appeals against penalties succeed where there is a reasonable excuse such as serious illness or a bereavement close to the deadline, but not for forgetting, finding the system difficult or relying on an agent who missed the date. A Time to Pay arrangement can be set up online for bills up to £30,000 to spread the payment over up to twelve months, with interest but without late payment penalties.
Making Tax Digital for Income Tax
Sole traders and landlords whose combined gross self-employment and property income was over £50,000 in 2024/25 have been required since 6 April 2026 to keep digital records and send quarterly updates through compatible software, followed by a final declaration in place of the annual return. The threshold falls to £30,000 of income in 2025/26 from 6 April 2027 and to £20,000 of income in 2026/27 from 6 April 2028. Quarterly updates are due by 7 August, 7 November, 7 February and 7 May, and the payment dates are unchanged. A trader above the threshold who has not yet signed up should do so before the first quarterly deadline, as a new points-based penalty regime applies to late submissions.
Common questions
When is the Self Assessment deadline? 31 January 2027 for online returns and payment for the 2025/26 tax year. Paper returns are due by 31 October 2026 and new registrations by 5 October 2026.
What are payments on account? Two advance payments towards the current year’s bill, each half of the previous year’s, due on 31 January and 31 July, required where the previous bill was over £1,000 and less than 80% was collected at source.
Why is my first January bill so large? It combines the whole of the previous year’s tax with the first payment on account for the current year, so it is one and a half times the annual bill.
What is the penalty for filing late? £100 immediately, then £10 a day after three months up to £900, then 5% of the tax or £300 at six and twelve months. Late payment adds 5% at 30 days, six months and twelve months plus interest.
Do I need to file if I am employed and have a side business? Yes if the side business brings in more than £1,000 in a tax year. Below that the trading allowance covers it and no return is needed for that income alone.
What is Making Tax Digital for Income Tax? Quarterly digital reporting for sole traders and landlords, compulsory from April 2026 for income over £50,000, April 2027 over £30,000 and April 2028 over £20,000.
Information, not tax advice. Deadlines, thresholds and penalties are the published rules on gov.uk: Self Assessment deadlines, gov.uk: payments on account and gov.uk: Making Tax Digital for Income Tax; worked figures are from the site’s calculator for a sole trader with no other income. Take advice on your own return before acting on them.