Key facts
- The 2026/27 return is due online by 31 January 2028; paper returns by 31 October 2027
- The 2026/27 tax year runs from 6 April 2026 to 5 April 2027
- Late filing triggers an automatic £100 penalty; penalties can reach about £1,600 by 12 months
- Late payment on a £5,000 bill adds £250 at 30 days, £500 at six months and £750 at twelve months, plus 8% interest
Work out what you owe before you file with the limited company tax calculator and the dividend tax calculator, and check how your bands work in income tax bands guide.
| Task | Deadline |
|---|---|
| Register if newly self-employed | 5 October 2027 |
| File a paper tax return | 31 October 2027 |
| File online | 31 January 2028 |
| Pay the tax you owe, plus first payment on account | 31 January 2028 |
| Second payment on account | 31 July 2028 |
For the 2026/27 tax year (6 April 2026 to 5 April 2027). Source: HMRC, verified 16 June 2026.
If you are a subcontractor, your deductions feed into the return: see CIS deductions guide, and how National Insurance fits in National Insurance rates guide.
Who must file a self assessment tax return
| Circumstance | Self assessment required? |
|---|---|
| Self-employed with net profits above £1,000 | Yes |
| Partner in a business partnership | Yes |
| Director of a limited company (unless dormant with no income) | Yes |
| Income above £100,000 in the tax year | Yes |
| Rental income above £2,500 (or above £10,000 gross) | Yes |
| Capital gains above the £3,000 exempt amount | Yes |
| Untaxed income above £2,500 | Yes |
| Child Benefit received and income above £60,000 | Yes (High Income Child Benefit Charge) |
| Foreign income | Yes |
| PAYE employee with additional income | Often yes |
If you are unsure whether you need to file, HMRC provides a checking tool at gov.uk/check-if-you-need-to-send-a-self-assessment-tax-return. New sole traders can read our sole trader tax guide for Income Tax, Class 4 NI, and registration in 2026/27.
Key deadlines for the 2026/27 return
The deadline for online returns for the 2026/27 tax year is 31 January 2028. Paper returns are due by 31 October 2027. Newly self-employed filers must register by 5 October 2027.
| Action | Deadline |
|---|---|
| Register for self assessment (new filers) | 5 October 2027 |
| File paper tax return | 31 October 2027 |
| File online tax return | 31 January 2028 |
| Pay any outstanding tax for 2026/27 | 31 January 2028 |
| Pay the tax you owe, plus first payment on account | 31 January 2028 |
| Second payment on account | 31 July 2028 |
The payment on account system: the biggest first-year shock
Payment on account catches almost every first-time self assessment filer by surprise. HMRC requires you to make advance payments toward your next year's tax bill, in addition to paying what you owe for the current year.
If your tax bill for 2026/27 (due 31 January 2028) exceeds £1,000 and more than 80% of your tax was not deducted at source (PAYE), HMRC requires you to make two payments on account for 2027/28:
- First payment on account: 50% of your 2026/27 bill, due 31 January 2028
- Second payment on account: 50% of your 2026/27 bill, due 31 July 2028
Worked example
Your self assessment tax bill for 2026/27 is £5,200.
- Balancing payment for 2026/27: £5,200 (due 31 January 2028)
- First payment on account for 2027/28: £2,600 (due 31 January 2028)
- Total due by 31 January 2028: £7,800
Many new filers who have saved only £5,200 are shocked to find £7,800 is due in January. Plan for this by treating 50% of your annual tax bill as a deposit that will be required with your first return.
If your 2027/28 income is expected to be lower, you can apply to reduce your payments on account using HMRC's online service. If you reduce them and your actual bill turns out higher, you will pay interest on the shortfall.
Self Assessment Calculator
Estimate your full 2026/27 tax bill including payments on account.
Expert Tip
The most effective way to reduce your self assessment bill is to make pension contributions before the end of the tax year (5 April 2027). Contributions to a registered pension scheme reduce your adjusted net income, which affects income tax, the High Income Child Benefit Charge (if relevant), and the personal allowance taper above £100,000. A pension contribution made on 4 April 2027 carries the same tax benefit as one made at the start of the year.How to file: step-by-step
Step 1: Register - If you have never filed self assessment before, register with HMRC at gov.uk/register-for-self-assessment. For self-employed individuals, registration must be completed by 5 October following the end of the tax year.
Step 2: Gather your records - You will need: P60 from any employment, P11D for any benefits in kind, records of self-employment income and expenses, rental income and mortgage interest statements, bank interest statements, dividend records, any capital gain documentation.
Step 3: Complete the return - Log into HMRC's Self Assessment Online service or use HMRC-approved third-party software. Complete all relevant sections for your income types.
Step 4: Submit and pay - Submit the 2026/27 return by 31 January 2028. Pay the balance owed (including payments on account if applicable) by the same date.
Allowable expenses for the self-employed
For a full breakdown of what you can claim, simplified flat rates, and the trading allowance, see our self-employed expenses guide.
Self-employed income is taxed on net profit: revenue minus allowable business expenses. The most common allowable expenses:
| Expense category | Examples |
|---|---|
| Office costs | Stationery, printing, software subscriptions, broadband |
| Travel | Business mileage (45p/mile for first 10,000 miles, 25p/mile after), parking, public transport |
| Clothing | Protective or uniformed workwear only (not normal business attire) |
| Staff costs | Employee wages, employer NI, recruitment costs |
| Financial costs | Accountancy fees, bank charges, business loan interest |
| Marketing | Advertising, website costs, social media |
| Professional fees | Professional subscriptions relevant to the trade |
| Home working | Proportion of home costs if working from home (flat rate or actual proportion) |
Personal expenses are not deductible. Mixed-use items must be apportioned. The Trading Allowance (£1,000) allows microbusinesses to deduct a flat £1,000 instead of itemised expenses, if actual expenses are lower.
Penalties for late filing and payment
Miss the filing deadline and HMRC charges an automatic £100, even if you owe no tax. After 3 months, daily penalties of £10 add up to a further £900. At 6 months and again at 12 months, you pay the higher of £300 or 5% of the tax due, so a return that is 12 months late reaches about £1,600 in fixed penalties before interest. Late payment is separate: 5% of the unpaid tax at 30 days, again at 6 months and at 12 months, with interest currently at 8% a year on top.
| Delay | Penalty |
|---|---|
| Return filed 1 day to 3 months late | £100 automatic penalty |
| Return filed 3 to 6 months late | £10 per day (up to £900 additional) |
| Return filed 6 to 12 months late | 5% of the tax due or £300, whichever is greater |
| Over 12 months late | Further 5% or £300, penalties can reach 100% of tax owed |
| Tax paid 30 days late | 5% surcharge on unpaid tax |
| Tax paid 6 months late | Further 5% surcharge |
| Tax paid 12 months late | Further 5% surcharge |
Interest also accrues on outstanding payments from the due date, currently at 8% a year.
Making Tax Digital for Income Tax (MTD for IT)
From April 2026, self-employed individuals and landlords with income over £50,000 are required to use MTD-compatible software to keep digital records and submit quarterly updates to HMRC. From April 2027, the threshold drops to £30,000. This replaces the annual self assessment return with quarterly digital submissions and an end-of-period statement.
If your income is above these thresholds, start preparing now by adopting compatible bookkeeping software (QuickBooks, Xero, FreeAgent, or HMRC's own free tools).
Related Calculators
Frequently Asked Questions
The 2026/27 return is due online by 31 January 2028, with paper returns by 31 October 2027, and any tax owed is also due by 31 January 2028. The second payment on account for 2026/27 is due by 31 July 2028.
An automatic £100 penalty applies on the day after the deadline, even if you owe no tax. Further daily penalties of £10 apply from day 91. File as soon as possible to limit additional charges.
Advance payments toward your next year's tax bill, required when your tax liability exceeds £1,000 and you do not have significant PAYE income. Two payments are required: 50% by 31 January and 50% by 31 July.
Yes, if you expect your income to be lower in the following year. Apply online through your HMRC account. If you reduce the payments but your actual bill is higher, HMRC charges interest on the shortfall.
Yes. Class 4 NI (6% on profits between £12,570 and £50,270, 2% above) is calculated and collected through your self assessment return alongside income tax.
Keep records for at least five years from the 31 January submission deadline. This includes bank statements, invoices, receipts, mileage logs, and any other evidence of income and expenses.
Contact HMRC before the deadline. HMRC offers a Time to Pay arrangement that allows the debt to be spread over monthly instalments. Penalties still apply for late payment unless an arrangement is agreed in advance.
Not if all your income is taxed through PAYE and you have no other taxable income above £1,000, rental income, dividends above the allowance, or capital gains above the exempt amount. If any of those apply, you must register for self assessment by 5 October after the tax year end.
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James Hartley is a Chartered Management Accountant (CIMA) with more than eight years of experience in UK tax, payroll and compliance. He holds a BSc in Finance and Economics from the University of Manchester and spent his early career at a Big 4 accounting firm. He founded WhatsUK to build free UK financial calculators and guides verified against official HMRC sources. He authors every calculator and article on WhatsUK.
Sources & Official References
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Disclaimer: This calculator provides estimates based on standard HMRC rates for 2026/27. Results may vary based on individual circumstances. This is not financial advice. Always consult a qualified accountant or CIMA-qualified financial adviser for personal tax matters.