Comparison Guide · Updated June 2026
Accountant vs DIY Self Assessment UK 2026: Is It Worth the Cost?
DIY self assessment using HMRC's free online service costs nothing and takes 10–15 hours the first time (2–4 hours once you know what you are doing). A UK accountant charges £150–£500 for a basic sole trader return. The real question is not the fee — it is whether a professional will spot deductions and planning opportunities worth more than their cost, and whether your situation is genuinely complex enough to risk filing alone. This 2026/27 guide gives you the numbers and the decision framework.
At a Glance: Accountant vs DIY Self Assessment
| Factor | Use an Accountant | DIY Self Assessment |
|---|---|---|
| Annual cost | £150–£500 (sole trader); £800–£2,000+ (Ltd) | £0 HMRC online; £40–£80 commercial software |
| Time required | Minimal — gather records, accountant files | 10–15 hrs first time; 2–4 hrs thereafter |
| Accuracy risk | Low — professionals carry PI insurance | Moderate — errors common without guidance |
| Missed allowances | Accountant proactively identifies savings | Easy to overlook deductions and reliefs |
| HMRC enquiry support | Handled by accountant (fee or included) | You deal with HMRC correspondence alone |
| MTD from April 2026 | Accountant manages quarterly submissions | Requires MTD-compatible software (not free HMRC) |
| Tax planning | Active: pension timing, dividend strategy | Passive: tax calculated on what you enter |
| Best suited to | Ltd company, IR35, property, complex income | Simple sole trader, PAYE + small side income |
How Much Does a UK Accountant Cost in 2026?
Accountancy fees vary significantly by complexity, region, and whether you use a local firm or an online service. Typical 2026/27 benchmarks:
| Situation | Typical fee (2026) | Net after tax relief |
|---|---|---|
| PAYE employment + small side income | £150–£250/yr | ~£108–£180 (basic rate) |
| Sole trader, simple return | £250–£400/yr | ~£150–£240 (40% taxpayer) |
| Sole trader + VAT + bookkeeping | £700–£1,200/yr | ~£420–£720 (40%) |
| Ltd company accounts + CT600 + director SA | £1,000–£1,800/yr | ~£750–£1,350 (25% CT) |
| Ltd company + payroll + VAT + P11D | £1,800–£3,000+/yr | ~£1,350–£2,250 (25% CT) |
London accountants typically charge 20–40% more than regional firms. Online accountancy services (Crunch, Gorilla Accounting, SJD) often bundle Ltd company accounts from £80–£130/month. Accountancy fees are a deductible business expense — net cost estimates assume income tax or corporation tax relief as stated. Actual fees vary — always obtain written quotes from multiple practices.
What DIY Self Assessment Actually Involves
Filing your own return via HMRC's Government Gateway is free and legally straightforward. The SA100 main return with supplementary pages covers every income type:
- SA102 — employment income (P60 and P11D data)
- SA103S / SA103F — self-employment income and expenses (short or full form)
- SA105 — UK property income
- SA108 — capital gains (shares, property, other assets)
- SA106 — foreign income
HMRC's online service calculates your tax, Class 2 National Insurance (where applicable), and Class 4 NI automatically once you enter your figures. The 2026/27 rates it applies:
- Income tax: 20% (basic), 40% (higher, income above £50,270), 45% (additional, above £125,140)
- Personal Allowance: £12,570 (tapered to zero between £100,000–£125,140)
- Class 4 NI: 6% on profits £12,570–£50,270; 2% above £50,270
- Class 2 NI: abolished from April 2024 — no longer applicable
- Dividend allowance: £500 (2026/27)
- Personal Savings Allowance: £1,000 (basic rate); £500 (higher rate); £0 (additional rate)
Time commitment: first-time filers typically spend 10–15 hours gathering records, understanding allowable expenses, navigating the online forms, and checking the calculation. After the first year, the same return typically takes 2–4 hours because you know what you need and where it goes.
Worked Example: When an Accountant Pays for Itself
Sarah is a higher-rate taxpayer who works full-time as a marketing manager (£62,000 PAYE salary) and also runs a freelance copywriting side income earning £18,000/year in 2025/26. She rents out a room under Rent a Room Relief and earns £7,500 — just at the exemption limit.
Filing DIY, Sarah enters her £18,000 self-employment income and claims obvious expenses: laptop software £240, a proportion of her phone bill £180, professional memberships £195. She claims £615 in expenses and pays tax on £17,385.
Her accountant, reviewing the same income, additionally identifies:
- Home office use of property — Sarah works from home 3 days per week. Applying HMRC's simplified flat rate (£26/month for 101–140 hours/month) gives £312/year, or using actual cost apportionment on her £1,800 annual broadband, heating, and electricity gives a higher figure of £540. Accountant uses actual costs: additional £540 deducted.
- Capital allowances on equipment — Sarah bought a dedicated work laptop at £950 and a second monitor at £280 last year and did not claim capital allowances. She claimed only the software on a simple expenses basis. The accountant claims Annual Investment Allowance on both items: £1,230 additional deduction in full (100% AIA for assets used wholly for business).
- Pension contribution timing — Sarah earns £80,000 total adjusted income. She is close to the £100,000 threshold where Personal Allowance starts tapering. The accountant advises a £15,000 pension contribution before 5 April, which reduces adjusted income to £65,000, preserving her full Personal Allowance (worth £5,028 in retained allowance). Tax saving: £5,028 × 40% = £2,011.
- Prior-year losses carried forward — In 2023/24, Sarah made a £600 loss in her first year of freelancing. She did not know losses could be carried forward. The accountant applies this against 2025/26 profits: additional £600 deduction.
Summary: DIY vs Accountant for Sarah
| Item | DIY | With accountant |
|---|---|---|
| Gross self-employment income | £18,000 | £18,000 |
| Expenses claimed | £615 | £2,985 |
| Prior-year losses applied | £0 | £600 |
| Taxable self-employment profit | £17,385 | £14,415 |
| Pension contribution (personal) | £0 | £15,000 |
| Tax saved vs DIY baseline | — | ~£3,100 |
| Accountant fee (net after tax relief) | — | ~£270 |
| Net benefit of using accountant | — | ~£2,830 |
Figures simplified for illustration. Tax savings depend on individual circumstances. Pension contribution assumes Sarah can afford and chooses to make the contribution — the accountant identifies the opportunity, not the cash. Accountant fee net cost assumes £450 gross fee with 40% income tax relief.
The key insight: for a sole trader filing a genuinely simple return with a single income source and obvious expenses, DIY is perfectly adequate and saves £250–400/year. For anyone with a higher income, multiple income sources, a pension planning opportunity, or unreclaimed prior losses, the accountant frequently identifies savings that dwarf the fee.
HMRC Investigation Risk: Does DIY Increase It?
HMRC opens around 300,000 formal enquiries annually — approximately 1% of all self assessment returns. Enquiries fall into three categories:
- Aspect enquiries: HMRC queries one specific item (often expenses or income that looks inconsistent with sector averages). Most common and least invasive.
- Full enquiries: a complete review of the return. Typically triggered by significant inconsistencies, tip-offs, or random selection.
- Random enquiries: HMRC selects a proportion of returns entirely at random as a control mechanism — no fault implied.
Common DIY errors that increase enquiry risk:
- Claiming expenses that HMRC's sector benchmarks flag as unusually high as a proportion of turnover
- Missing income that HMRC already holds from third-party data (bank interest notifications, PAYE records, Companies House filings)
- Turnover inconsistent with VAT returns or prior-year filings
- Using the £1,000 Trading Allowance and also claiming actual expenses (mutually exclusive — HMRC will query this)
- Incorrectly reporting capital gains — the most frequently missed item on DIY returns
An accountant does not eliminate random enquiry risk, but they do reduce the risk of triggering an aspect enquiry through data entry errors or inconsistent figures. Crucially, if HMRC does open an enquiry, having a professional handle the correspondence is far more effective and far less stressful than self-representation. Many accountants include fee protection insurance in their packages — typically adding £50–£100/year to their fee — which covers the cost of defending an enquiry.
When You Genuinely Need a Professional
The following situations carry meaningful complexity and risk if attempted without professional guidance:
- Ltd company directorship: company accounts must comply with Companies Act 2006, the Corporation Tax CT600 requires knowledge of allowable deductions and reliefs, and dividend vs salary optimisation for 2026/27 (with corporation tax at 25% above £250k profits) is non-trivial.
- IR35 (off-payroll working): contractors inside IR35 within the public sector or at large private sector engagers face deemed employment rules. Incorrect status determination can result in years of back tax plus interest and penalties. Specialist IR35 advisers are essential.
- Property portfolio: allowable repairs vs capital improvements, Replacement of Domestic Items Relief, mortgage interest restriction (Section 24 — you can only deduct a 20% tax credit, not the full interest), ATED on properties above £500,000, and CGT on disposal all interact in ways that DIY filing routinely gets wrong.
- Employment plus self-employment in the same year: the interaction of PAYE Class 1 NI and self-employed Class 4 NI, including the deferment of NI on the higher earner, is mishandled in a significant minority of DIY returns.
- Share scheme awards: EMI option exercise, CSOP grants, SAYE maturity, and unapproved option gains all have distinct tax treatment with different reporting deadlines. Errors are costly and attract penalties.
- HMRC enquiry: if HMRC has already opened an enquiry, engage a tax professional immediately. Do not attempt to handle a formal HMRC investigation without professional support.
Making Tax Digital for ITSA: Impact from April 2026
Making Tax Digital for Income Tax Self Assessment (MTD for ITSA) changes the filing landscape significantly:
- From April 2026: self-employed individuals and landlords with qualifying income above £50,000 must keep digital records and submit quarterly updates to HMRC via MTD-compatible software.
- From April 2027: extended to those with income above £30,000.
- From April 2028: those with income above £20,000 (proposed).
HMRC's free online self assessment service is not MTD-compatible. If MTD applies to you from April 2026, you must use approved software: FreeAgent, Xero, QuickBooks, Sage, or a range of smaller MTD-approved apps. An accountant using an MTD-compatible practice management platform can handle quarterly submissions on your behalf — often included in their standard annual fee.
For those not yet mandated (income below £50,000 for 2026/27), the existing annual return process continues. DIY via free HMRC software remains available.
Commercial Software: The Middle Ground
Between the free HMRC service and a full accountant sits a range of commercial self assessment software that provides better guidance, error checking, and the ability to handle more complex returns:
- GoSimpleTax (~£50/year): popular with sole traders, clear guidance, handles property and capital gains, tax saving suggestions
- TaxCalc Individual (~£40–£80/year): professional-grade, handles all SA pages including complex foreign income, used by many accountants and sophisticated individuals
- FreeAgent (free with NatWest/RBS/Mettle business accounts; ~£19/month otherwise): full bookkeeping plus SA filing, MTD-compliant, excellent for growing sole traders who want a real-time P&L view
- QuickBooks Self-Employed (~£8–£15/month): automated expense categorisation from bank feeds, mileage tracking, SA103 export
Commercial software reduces the error risk significantly compared to HMRC's basic online form — flagging inconsistencies and prompting for commonly overlooked items. It is a good middle-ground option for a moderately complex sole trader return where the full cost of an accountant is hard to justify but DIY on the HMRC service feels risky.