You do not legally need an accountant to file a Self Assessment return, but one is worth it if you are self-employed, a landlord, a company director, have income from abroad, or sold assets during the year. For the 2025/26 tax year, online returns and any tax owed are due by 31 January 2027. An accountant makes sure the figures are right, the reliefs are claimed and the deadline is met.
KEY FACTS
- Paper returns for 2025/26 are due by 31 October 2026; online returns by 31 January 2027.
- Tax owed for 2025/26 and the first payment on account for 2026/27 are both due on 31 January 2027.
- Missing the filing deadline brings an immediate £100 penalty, even if no tax is owed.
From April 2027, Making Tax Digital for Income Tax applies to qualifying income above £30,000.
Who Has to File a Self Assessment Return?
You usually need to file if you were self-employed with income over £1,000, received rental income, were a partner in a business, had untaxed income such as foreign income, or need to pay the High Income Child Benefit Charge. Company directors with dividends or other untaxed income often need one too. If you are not sure, HMRC’s online checker is a good starting point, or a self assessment accountant can confirm it in one conversation.
Key Deadlines for the 2025/26 Tax Year
Here are the dates to plan around:
| Date | What is due |
| 31 October 2026 | Paper tax return deadline |
| 30 December 2026 | Online return deadline if you want tax under £3,000 collected through your PAYE tax code |
| 31 January 2027 | Online tax return, balancing payment for 2025/26 and first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
Late filing costs £100 straight away. After three months, daily penalties of £10 a day can add up to £900, with further penalties at six and twelve months. Late payment adds interest and its own percentage penalties on top.
What Does an Accountant Actually Do?
A good tax return accountant does more than type figures into HMRC’s system. They will:
- Gather and check your income records, bank statements and expense receipts.
- Claim the expenses and allowances you are entitled to, and leave out the ones HMRC would challenge.
- Work out payments on account and tell you exactly what to pay and when.
- Spot tax-saving opportunities, such as pension contributions or using a spouse’s allowances.
- Deal with HMRC on your behalf if there are questions or an enquiry.
They also look ahead. If your 2025/26 return shows qualifying self-employment and property income above £30,000, Making Tax Digital for Income Tax will apply to you from April 2027, with quarterly updates through compatible software. An accountant can set that up before the first deadline arrives.
How Much Does an Accountant Cost for Self Assessment?
The fee depends on how much work your return involves, not on how much you earn. A single source of employed income with one rental property is quicker to prepare than a return covering a sole trade, several properties, foreign income and a capital gain. The state of your records also matters: tidy, digital records cost less to process than a shoebox of receipts.
Ask for a fixed quote before work starts, and check what it covers, such as payments on account advice, HMRC correspondence and a review of next year’s position. In many cases, the reliefs an accountant identifies and the penalties you avoid more than cover the fee.
When You Can Do It Yourself
If your only extra income is a small, simple amount and your records are in order, filing yourself can be straightforward. Once you have self-employment, rental property, foreign income or a pension charge in the mix, the risk of a costly mistake goes up.
If you want a personal tax accountant in London, Allenby Accountants prepares Self Assessment returns for sole traders, landlords, directors and professionals across the capital. Local clients can visit our team of accountants in Uxbridge at Brook House, Cowley Mill Road.
Frequently asked questions
Can I file my own Self Assessment return?
Yes. Anyone can file through HMRC’s online service, but an accountant reduces the risk of errors and missed reliefs.
What happens if I miss the 31 January 2027 deadline?
You get an automatic £100 penalty, with more penalties and interest the longer the return or tax stays outstanding.
Will Making Tax Digital replace my tax return?
Not entirely. You will send quarterly updates and then a final return after the year end, still due by 31 January.
Get Your 2025/26 Return Done Early
Call 0208 914 8887 or email info@allenbyaccountants.co.uk for a free, no-obligation consultation.
