January approaches, the Self Assessment deadline looms, and you are staring at the question every UK freelancer, landlord and side-hustler eventually faces: do I pay an accountant £150–£300 to file my tax return, or do it myself for free? The good news is that filing your own UK tax return is entirely doable — HMRC’s online system is designed for it, millions do it annually, and the actual cost can be £0. But “free” has fine print: your time, the risk of errors, and the situations where DIY becomes false economy. This guide breaks down what it really costs to file without an accountant, when DIY makes sense, and how to do it right.
The True Cost of DIY Filing: £0 (Plus Your Time)
HMRC’s online Self Assessment filing is free — no submission fee, no hidden charges. The real costs are: your time (3–10 hours for a straightforward return the first time, 1–3 hours once you know the system); record-keeping effort through the year (the filing is easy if the records exist; agonising if they do not); and risk (errors can mean overpaid tax you never reclaim, or underpaid tax plus penalties and interest).
Optional costs that are worth considering: bookkeeping software (£10–£25/month, free tiers exist) that categorises income and expenses through the year and can submit directly to HMRC; and a one-off “check my return” review by an accountant (£75–£150) — the hybrid option that buys professional assurance at a fraction of full-service cost.
When DIY Filing Makes Sense
File yourself confidently if: you are a sole trader with straightforward income and expenses; you are employed with simple additional income (rental from one property, modest freelance work); your affairs fit neatly into HMRC’s online boxes; and you keep decent records. The online system guides you question by question — it is closer to a well-designed questionnaire than to tax law. Registering as self-employed with HMRC is the first step if you have not already, and the filing flows naturally from the records that registration requires you to keep.
When an Accountant Pays for Themselves
Hire one (or at least buy a review) if: you run a limited company (corporation tax, dividends, payroll — genuinely complex); you have multiple income sources interacting (employment + rental + freelance + investments); you sold assets with capital gains complications; you are unsure about expense claims (the rules on allowable expenses are where most DIY filers either overpay through caution or underpay through optimism); you were investigated before; or the amounts are large enough that a 10% error dwarfs the accountant’s fee. There is also a middle category people overlook: the first year of something new. Going self-employed for the first time, buying your first rental property, or receiving your first dividends are all moments when a single year of professional help — learning what “correct” looks like — pays dividends (so to speak) for every DIY year that follows. Think of it as tuition, not an ongoing cost. The accountant’s value is not the form-filling — it is knowing what you did not know to claim. Understanding how sole-trader profits are taxed helps you judge whether your situation has outgrown DIY.
The DIY Process: Step by Step
1. Register (if new). Register for Self Assessment by 5 October following the tax year — HMRC posts you a Unique Taxpayer Reference; allow weeks. Keep the Government Gateway credentials safe; losing them in January is a classic self-inflicted crisis.
2. Gather records. All income (invoices, P60s, bank interest, rental statements), all expenses with receipts, pension contributions, charitable donations (Gift Aid), and student loan details. The filing takes an evening; the gathering takes the time — keep records monthly and this step vanishes. A practical tip: create a single folder (physical or digital) where every tax-relevant document goes the moment it arrives, all year. January-you will be profoundly grateful to March-you.
3. Complete the online return. Log in, answer the tailored questions, enter figures in the boxes. The system calculates your bill automatically. Take your time; save and return as needed.
4. Review ruthlessly. Check every figure against your records. Common DIY errors: forgetting income sources, misclassifying expenses, missing pension relief, and transposition typos. A second pair of eyes — even a numerate friend — catches what familiarity misses.
5. Submit and pay by 31 January. Online submission deadline and payment deadline coincide. Late filing starts at £100 penalties escalating daily — diarize it now. Note the payments-on-account system: if your tax bill exceeds £1,000, HMRC may require advance payments toward next year’s bill — a cash-flow surprise that catches first-time filers. Budget for it: your first January payment can be roughly 150% of what you expected (this year’s bill plus half of next year’s in advance).
The Hidden Costs of Getting It Wrong
Underpaid tax accrues interest from the due date plus penalties scaled to behaviour — careless errors cost up to 30% of the tax due; deliberate ones far more. Overpaid tax is quieter but equally real: unclaimed expenses, missed allowances and unrelieved pension contributions are money left on HMRC’s table. There is a third cost people forget: the enquiry. If HMRC opens an investigation into your return, the time, stress and potential professional fees dwarf any saving from DIY filing — which is why accurate, well-documented returns matter more than cheap ones. Keep perspective, though: for straightforward returns, the error risk is modest and the system forgiving of honest mistakes corrected promptly. The fear of filing is usually worse than the filing.
Conclusion
Filing your UK tax return without an accountant costs £0 in fees plus an evening of your time — and for straightforward sole traders and simple additional incomes, that is all it needs to cost. The decision rule: DIY when your affairs fit HMRC’s boxes and your records are sound; buy a professional review when complexity, large sums or uncertainty enter the picture. Either way, the real cost-saver is not the filing method — it is the monthly record-keeping habit that makes January boring instead of terrifying.
Frequently Asked Questions
Is it free to file a tax return with HMRC?
Yes — online Self Assessment filing is completely free. Your costs are time and record-keeping effort; optional bookkeeping software or a professional review are the only potential expenses.
When is the UK tax return deadline?
31 January for online filing and payment (following the tax year ending 5 April). Paper returns have an earlier 31 October deadline. Register for Self Assessment by 5 October if filing for the first time.
What happens if I file late?
An immediate £100 penalty, escalating with continued delay, plus interest on unpaid tax. Diarize the deadline — late filing is the most expensive avoidable mistake in the system.
Do I need an accountant as a sole trader?
Not necessarily — straightforward sole-trader returns are very DIY-able. Consider one if your affairs are complex, sums are large, or you are unsure about expense claims; a one-off review is a cost-effective middle ground.
What records do I need to keep?
All income evidence, expense receipts, bank statements, pension and Gift Aid records — kept for at least five years after the filing deadline. Monthly record-keeping turns January filing into a non-event.
