Self-Assessment Tax Return Accountants UK 2026

A UK Self Assessment tax return can be filed two ways: do it yourself through HMRC’s online service, or pay a Self Assessment accountant to check it or complete it for you. Neither route is compulsory and neither is automatically the cheaper one. A basic one-off filing starts from £50 a year, while a fuller service or a monthly package costs more but buys ongoing support rather than a single form. This guide sets out who HMRC expects to file, the deadline calendar for the 2025-26 tax year, and what a Self Assessment accountant actually costs against doing it yourself.

Every deadline and threshold below is taken directly from GOV.UK. Every price is read from a UK accountancy firm’s own published pricing page, verified in August 2026. Where a rule is not yet verified against a primary source, such as late-filing penalty amounts or National Insurance rates, this guide says so and points to GOV.UK instead of guessing at a figure.

Who Needs to File a Self Assessment Return

HMRC lists several categories of people who normally need to complete a Self Assessment return, rather than having all of their tax collected automatically through PAYE. These include the self-employed, including sole traders; partners in a business partnership; company directors with income not fully taxed at source; landlords with rental income; people with other untaxed income, such as savings, investments or dividends; people with foreign income; and higher earners with more complex tax affairs. This is a structural list, not personal advice, and it is not exhaustive.

Whether any individual return is actually required depends on figures HMRC has not published in a form this guide can verify, so we are not stating specific income thresholds here. HMRC runs its own online tool to check whether you personally need to file, and that tool, not a general guide, is the right place to get a definitive answer.

Registering for Self Assessment for the first time, if you haven’t done it before, is a separate step from filing the return itself, and it has its own registration deadline that HMRC sets out on GOV.UK. If the checker confirms you need to file, the next question is whether to do it yourself or pay for help, which is what the rest of this guide covers.

Self Assessment Deadlines for the 2025-26 Tax Year

The current Self Assessment tax year runs 6 April 2025 to 5 April 2026. If you file on paper, that return is due by 11:59pm on 31 October 2026. Almost everyone files online instead, and the online deadline is 11:59pm on 31 January 2027, which is also the date any tax owed must be paid.

If HMRC is collecting part of what you owe through your PAYE tax code, for example because you also have an employed job, the deadline to submit online for that route moves earlier, to 30 December 2026. Some people also make a second payment on account towards the following year’s tax bill, due by 31 July, on top of the January payment. Missing the January deadline triggers an automatic late-filing penalty from HMRC, even if no tax is actually owed, so the filing date matters as much as the payment date.

We are deliberately not stating the size of the late-filing penalty here, or the interest rate HMRC charges on tax paid after 31 January. HMRC’s penalty and interest figures change and this guide has not verified a current number against a primary source, so an accountant or GOV.UK directly are the places to confirm what a specific late return or late payment would actually cost you.

What an Accountant Does That Filing Yourself Doesn’t

HMRC’s online Self Assessment system was built for one person to complete their own return, and for straightforward affairs it works well: enter your income and expense figures, and the system calculates what you owe. A Self Assessment accountant does the same data entry but adds a check on what you’ve included before it goes to HMRC, catches expense categories a non-accountant might miss or misclassify, and answers questions about specific purchases or income types as they come up. See our guide to what an accountant actually does for the full breakdown of these tasks. None of that changes the deadlines above, and none of it is compulsory. It is a judgement about whether your own confidence in the numbers is worth paying to reinforce.

For sole traders specifically, our guide to accountants for sole traders covers the point where a self-employed return becomes complex enough that paying for help typically pays for itself, including VAT registration and taking on a first employee.

The Cheap One-Off Route vs a Monthly Package

Self Assessment accountants price their work in two different ways. A one-off filing costs the least and buys exactly one thing: your return checked and submitted. Cheaper Accountant’s basic Self Assessment starts at £50 a year, and Taxez offers the equivalent service from £59. A fuller sole trader filing, still a one-off job rather than a retainer, runs from £150 a year and typically includes a closer review of what you can claim. The alternative is a monthly package, where a fixed fee each month covers your return plus ongoing access to an accountant through the year. Our full accountant cost breakdown lists monthly package pricing across six UK firms if a retainer is the route you’re considering.

Company directors filing a personal Self Assessment alongside their limited company accounts usually pay this as an add-on rather than a standalone fee. At The Accountancy Partnership, that add-on runs from £10+VAT a month for each of the first two directors, and £10+VAT a month per additional director, on top of whatever the company’s own accounts package costs.

Neither route is objectively cheaper. A £50 one-off filing beats most monthly packages on price if you have exactly one straightforward return to submit each year. A package earns its cost back if you are the kind of filer who wants to ask questions before making a decision, not just after submitting the form.

Landlords and Property Income: A Different Filing Job

Rental income is filed as property income on Self Assessment, not as trading income, and accountants price it as a separate job from a standard return. Cheaper Accountant’s landlord Self Assessment service starts from £125 a year, above its £150-a-year sole trader rate, reflecting the extra detail a property return requires around allowable expenses and finance costs. If you have both a self-employed business and a rental property, expect a quote that covers both income sources rather than one flat sole trader price stretched to fit the second. The deadlines above apply equally to a landlord return: the same 31 January 2027 online cut-off, the same paper deadline of 31 October 2026.

A landlord juggling a rental property alongside other income sources is also the profile most likely to benefit from a monthly package rather than a one-off filing, simply because there is more to track across the year than a single trading income figure.

What Happens If You Miss the Deadline

Missing 31 January triggers an automatic late-filing penalty from HMRC, and further charges can apply the longer a return stays outstanding. This guide is not stating the amount of that penalty, or the interest rate HMRC applies to late payment, because neither figure has been verified against a current GOV.UK source for this piece. If a deadline is close and you are unsure where you stand, GOV.UK’s own penalty guidance is the accurate source, and an accountant can also file on your behalf at short notice, sometimes for an expedited fee.

If you think you have a reasonable excuse for missing the deadline, HMRC has a formal appeals process for that, separate from simply filing late. It is not a route to rely on by default, and this guide is not the place to judge whether a specific circumstance qualifies. An accountant who has filed an appeal before can usually tell you quickly whether it is worth pursuing, which is often faster than working through GOV.UK’s guidance alone under time pressure.

If cash flow, not the accountant’s fee, is the real pressure around deadline time, that’s a different problem with a different fix. Our guides to self-employed business loans cover funding gaps directly, rather than trying to solve them through a cheaper filing route.

Choosing the Right Route for Your Return

• Count how many questions you actually asked last year – if the honest answer is zero, a one-off filing at £50 to £150 likely beats a monthly package on cost.
• Check whether your income sources have grown – a rental property, a second income stream, or a first year of self-employment all add complexity a basic filing may not cover.
• Confirm what a “basic” filing excludes – a cheap headline price can still leave you doing all the bookkeeping yourself before you hand anything over.
• Ask for records early, not in January – most firms want your figures weeks before the deadline, and a rushed handover is where mistakes happen.
• Compare named firms, not category averages – our best online accountants comparison lines up specific providers rather than a generic price range.

If you’re still unsure, the cheapest route that matches your situation is usually the right starting point: file it yourself if HMRC’s checker confirms you have simple, single-source income; pay for a one-off filing if you want a second pair of eyes without a monthly commitment; and only move to a package once you have a genuine, recurring reason to ask an accountant questions between January deadlines. Tidier records also make either route cheaper to process, and tools covered in our spend management guide are built for exactly that.

Clara Wenslow

Finance & Business Services Editor

Clara analyses SME finance and procurement markets, covering business loans, invoice finance, payroll, and related B2B services. She ensures each comparison and guide is transparent and data-driven.

Reviewed by

Sarah Mitchell

B2B Commerce & Finance Reviewer