The big Self Assessment date is 31 January. By then you need to have filed your online return for the tax year that ended the previous April, paid whatever you still owe for that year, and, if you're in the payments on account system, made the first advance payment towards the current year. The second advance payment is due on 31 July.
The dates that matter most right now are for the 2025/26 tax year (6 April 2025 to 5 April 2026), whose online return and balancing payment are due by 31 January 2027.
Key dates
| Date | What's due | Example for 2025/26 |
|---|---|---|
| 5 October | Register for Self Assessment if you're new to it | 5 October 2026 |
| 31 October | Paper tax return deadline | 31 October 2026 |
| 31 January | Online return, balancing payment for last year, and 1st payment on account for this year | 31 January 2027 |
| 31 July | 2nd payment on account | 31 July 2027 |
You register by 5 October after the end of the first tax year in which you needed to file. So if you started trading in June 2026, that's in the 2026/27 tax year, and you have until 5 October 2027 to register. Missing that date can lead to a penalty if it means tax is paid late.
If you want HMRC to collect a bill of under £3,000 through your tax code instead of paying it in one go, and you're employed or get a pension, file online by 30 December.
How payments on account work
Payments on account are advance payments towards next year's bill. HMRC assumes your income will be roughly the same, so each one is half of your last bill.
They cover income tax and Class 4 National Insurance. They don't include capital gains tax or student loan repayments, which are paid with the balancing payment.
You don't have to make them if either of these is true:
- Your last Self Assessment bill was less than £1,000.
- More than 80% of your total tax for the year was already taken at source, usually through PAYE on a salary or pension.
So someone with a full-time job and a little rental income often avoids them, because most of their tax goes through payroll. A sole trader with no other income almost always pays them once their bill passes £1,000.
The first-year double payment
This is the bit that catches people out. In your first year of being self-employed, nobody collects anything in advance. Then on the first 31 January you pay the whole of last year's bill plus half of it again as the first payment on account for the current year.
Take a sole trader who starts in April 2026 and makes £30,000 profit in 2026/27:
- Income tax: (£30,000 − £12,570) × 20% = £3,486
- Class 4 NI: (£30,000 − £12,570) × 6% = £1,045.80
- Total bill for 2026/27: £4,531.80
| Date | Payment | Amount |
|---|---|---|
| 31 January 2028 | 2026/27 bill plus 1st payment on account for 2027/28 | £6,797.70 |
| 31 July 2028 | 2nd payment on account for 2027/28 | £2,265.90 |
That's £9,063.60 within six months, from a year's profit of £30,000. If you've been putting money aside since you started, it's fine. If you've only saved for the £4,531.80 bill, the January payment comes as a nasty surprise.
After that it settles down. Say your 2027/28 bill turns out to be £6,000. You've already paid £4,531.80 on account, so on 31 January 2029 you'd pay the £1,468.20 balance plus a first payment on account of £3,000 for 2028/29, which is £4,468.20.
Reducing payments on account
If you know this year's profits will be lower, perhaps because you've lost a big client or cut your hours, you can ask HMRC to reduce your payments on account. You can do this in your online account or on form SA303.
Be realistic about it. If you reduce them too far and your bill turns out higher, you'll be charged interest on the difference from the original due dates.
Penalties and interest
For a late return under the current rules:
| How late | Penalty |
|---|---|
| 1 day | £100, even if you owe nothing |
| 3 months | £10 a day, up to £900 |
| 6 months | 5% of the tax due or £300, whichever is more |
| 12 months | Another 5% or £300, whichever is more |
Late payment brings penalties of 5% of the unpaid tax at 30 days, 6 months and 12 months, on top of interest charged from the day the payment was due. Interest also applies to late payments on account, though there's no penalty for those.
Things are changing. Sole traders and landlords with qualifying income over £50,000 have had to use Making Tax Digital since April 2026, which brings quarterly updates and a points-based penalty system for late submissions. The income threshold is due to fall to £30,000 from April 2027. If you're in Making Tax Digital, check HMRC's guidance for the penalty rules that apply to you.
If you can't pay in full, contact HMRC before the deadline. If you owe £30,000 or less you may be able to set up a payment plan online, which stops late payment penalties building up, although interest still applies.
A simple way to stay ahead
- Move a fixed share of every payment you receive into a separate savings account. For a basic rate sole trader, 20% to 25% of profit is usually enough.
- In your first year, save for one and a half times the bill, not just the bill.
- File early. You can submit your 2026/27 return from 6 April 2027, and knowing the figure early gives you months to plan for January.
Work out your bill and your payment dates with the self-employed tax calculator. It shows the first-year payment on account automatically.
Last reviewed October 2026.