The main Self Assessment deadline is 31 January: your online tax return for the previous tax year and the tax you owe are both due by 11:59pm that day. For the 2025/26 tax year, that means 31 January 2027. The other dates to know are 5 October for registering, 31 October for paper returns, and 31 July for the second payment on account.
Note: this is general information, not tax advice. Dates and penalties are taken from GOV.UK at the time of writing, but they can change and your own circumstances may differ. Check GOV.UK or HMRC before relying on a date, and ask an accountant if your tax affairs are complicated.
The Self Assessment dates at a glance
Self Assessment runs on the tax year, which starts on 6 April and ends on 5 April. The return for the 2025/26 year (6 April 2025 to 5 April 2026) is the one being filed this winter. Here are the dates that matter:
| Date | What happens |
|---|---|
| 5 October 2026 | Deadline to tell HMRC you need to complete a tax return for 2025/26, if you have not filed one before |
| 31 October 2026 | Deadline for paper returns for 2025/26 (already passed) |
| 30 December 2026 | Online filing deadline if you want any underpaid tax collected through your tax code, where HMRC allows it |
| 31 January 2027 | Online return for 2025/26 due; tax owed for 2025/26 due; first payment on account for 2026/27 due |
| 5 April 2027 | End of the 2026/27 tax year |
| 31 July 2027 | Second payment on account for 2026/27 due |
| 5 October 2027 | Deadline to register for 2026/27, if you are new to Self Assessment |
| 31 January 2028 | Online return for 2026/27 due, and the tax and first payment on account for 2027/28 |
The 30 December date applies only if you owe tax and want it collected through your code, and there are conditions, so check GOV.UK for whether you qualify. Most people who file online simply aim for 31 January, but filing earlier gives you time to arrange payment and to avoid a last-minute rush.
Who has to file a tax return
Not everyone does. You usually need to send a tax return if you are self-employed and your income is above the £1,000 trading allowance, if you are a partner in a business partnership, or if you have other income that is not taxed at source, such as rental profits, savings or investment income above the allowances, or foreign income. You may also need to file if you have capital gains to report, or if your income is high enough to bring in other charges.
Many people file because of a one-off event: a property sale, a large share disposal or a change of circumstances. If you are unsure, use the “check if you need to send a tax return” tool on GOV.UK rather than guessing, because the rules depend on your situation. Self-employed tax explained: income tax, National Insurance and payments on account explains how profits are taxed, including Class 4 National Insurance.
A checklist before you file
Gathering your information early is the most useful thing you can do. Here is what to collect, in the order that most people need it:
- Your login details. You need your Unique Taxpayer Reference (UTR) and your Government Gateway user ID. If you have lost the UTR, HMRC can send a reminder, but that can take days or weeks, so ask early.
- Income records. Sales invoices, bank statements, platform statements and takings for the year.
- Expense records. Receipts, mileage, home-office costs and subscriptions. The alternative is the £1,000 trading allowance, which you cannot combine with deducting expenses.
- Employment documents. A P60 or final payslip, and any P11D for benefits.
- Savings and dividends. Interest and dividend statements.
- Pension and charity payments. Personal pension contributions and Gift Aid donations.
- Student loan and Child Benefit details, if they apply.
- Previous return. Last year’s figures help you spot omissions.
Set aside an hour to check that your records add up before you start entering numbers. A figure that is wrong because it was typed in a rush can lead to a letter from HMRC later.
Payments on account explained
Payments on account are advance payments towards next year’s bill. Once you are in the system, HMRC asks you to pay half of last year’s income tax and Class 4 National Insurance bill on 31 January and the other half on 31 July. You then settle any difference after the year ends. You do not need them if last year’s bill was under £1,000 or if more than 80% of your tax was collected at source, and you can ask to reduce them if you expect lower income.
Here is an illustration with round numbers. Suppose your 2025/26 income tax and Class 4 bill is £5,000 and you have never made payments on account before:
| Date | What you pay | Amount |
|---|---|---|
| 31 January 2027 | 2025/26 balancing payment | £5,000 |
| 31 January 2027 | First payment on account for 2026/27 (half of £5,000) | £2,500 |
| 31 July 2027 | Second payment on account for 2026/27 | £2,500 |
So on 31 January 2027 you pay £7,500 in one go, which surprises many first-time filers. The following January, when the actual 2026/27 bill is known, you compare it with the £5,000 paid on account. Using the House of Calculator estimate for a self-employed person with £40,000 of turnover and £8,000 of expenses (a profit of £32,000), the 2026/27 bill would be about £5,052 (£3,886 income tax plus £1,166 Class 4). That leaves a balancing payment of about £52, plus the first payment on account for 2027/28 of about £2,526. The numbers are illustrative: the real bill depends on the actual profit, other income and reliefs. Class 2 National Insurance is treated as paid at this profit level, so it does not add to the bill.
The first payments catch people out because they feel like paying two years of tax at once. Plan for it by setting money aside from the start of the year.
How much to set aside
A rule of thumb is to put away a share of each payment you receive. The estimate for £32,000 of profit above suggests setting aside about £421 a month, or 15.8% of profit. For other profit levels, the engine gives these 2026/27 figures with no other income:
| Profit | Income tax | Class 4 NI | Total | Set aside per month |
|---|---|---|---|---|
| £23,000 | £2,086 | £626 | £2,712 | £226 |
| £32,000 | £3,886 | £1,166 | £5,052 | £421 |
| £50,000 | £7,486 | £2,246 | £9,732 | £811 |
A student loan adds repayments through Self Assessment too. On a Plan 2 loan at £32,000 of profit, that is about £235 more. These are estimates, so add a margin and move the money to a separate savings account so it is not spent. Use the Self-Employed Tax and National Insurance Calculator for your own figures. The bill is for income tax and National Insurance on profit, not on takings, so keep your expenses records tidy.
Late filing and late payment penalties
GOV.UK sets out the penalties for missing deadlines:
| Late filing | Penalty |
|---|---|
| Return filed after the deadline | £100 |
| After 3 months | £10 a day, up to £900 |
| After 6 months | A further 5% of the tax due or £300, whichever is greater |
| After 12 months | A further 5% of the tax due or £300, whichever is greater |
| Late payment | Penalty |
|---|---|
| 30 days after the due date | 5% of the unpaid tax |
| 6 months | A further 5% |
| 12 months | A further 5% |
Interest is charged on unpaid tax as well. If you have a reasonable excuse, you can appeal a penalty. If you cannot pay in full by 31 January, contact HMRC before the deadline to ask about a payment plan, because acting early is better than staying silent. The £100 late filing penalty applies even if you owe no tax, so a return that shows nothing still has to be filed on time.
Making Tax Digital for Income Tax
Making Tax Digital for Income Tax changes how some self-employed people and landlords report. From 6 April 2026 it is required if your qualifying income (self-employment and property income before expenses) was over £50,000 in the 2024/25 tax year. The threshold falls to £30,000 from 6 April 2027 and £20,000 from 6 April 2028. Instead of one annual return, you keep digital records and send quarterly updates, then make a final declaration by 31 January after the year ends.
The quarterly updates are due on 7 August, 7 November, 7 February and 7 May for the standard quarters. If you may be affected, check GOV.UK to see whether you are in scope and whether you need compatible software. HMRC has said it will start signing up eligible people from September 2026, so look out for a letter.
A week-by-week plan to 31 January
- Now to the end of December: find your UTR and Gateway login, gather records, and make sure you can sign in.
- First week of January: enter your figures and check them against statements.
- Second week of January: file, and check HMRC’s calculation of the bill.
- By 20 January: arrange payment, which can take a few days to arrive. Use the reference on the payment slip.
- 31 January: deadline day for both filing and paying. Do not leave it to the last hour.
- After filing: diarise 31 July for the second payment on account and put money aside for it.
Common mistakes
- Missing the registration date. New self-employed people need to tell HMRC by 5 October after the end of the tax year.
- Forgetting that 31 January is also the payment deadline. Filing is not the same as paying.
- Not allowing for payments on account. The first January bill can be 150% of the previous year’s liability.
- Mixing up the tax year and the filing year. The return due in January 2027 is for the year to 5 April 2026.
- Claiming expenses and the trading allowance together. You have to choose one.
- Ignoring letters. A notice to file or a code change should be checked quickly.
Try the calculator
Enter your turnover, expenses and any student loan into the Self-Employed Tax and National Insurance Calculator to estimate income tax, Class 4 National Insurance and a monthly amount to set aside.
Frequently asked questions
What is the Self Assessment deadline for 2025/26?
The online return and the tax you owe are due by 11:59pm on 31 January 2027. The paper return deadline was 31 October 2026.
Do I have to pay by 31 January as well as file?
Yes. Both the return and the payment are due by 31 January. If you pay late you face a 5% penalty after 30 days, plus interest, even if you filed on time.
What are payments on account?
They are advance payments towards the next year’s bill, each half of the previous year’s income tax and Class 4 bill, due on 31 January and 31 July. You do not need them if your last bill was under £1,000 or more than 80% of your tax was collected at source.
What happens if I file my tax return late?
You get an automatic £100 penalty, even if you owe nothing, and further penalties build up after three, six and twelve months. You can appeal if you have a reasonable excuse.
Can I still register for Self Assessment now?
You were due to register by 5 October 2026 for the 2025/26 year, but you should still register as soon as you realise you need to, because the 31 January deadline is unchanged. Check GOV.UK for the current process.