DIY or Hire an Accountant for Your Self Assessment Return? Comparing Costs, Risks and Outcomes

If you need to complete a Self Assessment return, one of the first decisions is whether to file it yourself or hire an accountant.

For someone with straightforward income and organised records, completing a Self Assessment tax return yourself can be perfectly practical. However, if you are self-employed, have several sources of income, receive rental income, have capital gains or simply are not confident about tax rules, professional help may reduce errors and save considerable time.

The important question is therefore not simply, “Can I file my own Self Assessment return?”

It is:

“Is filing it myself the most sensible option for my circumstances?”

This guide compares DIY Self Assessment with hiring an accountant, including the potential costs, risks and outcomes. It also explains who may need to file, the key HMRC deadlines, allowable expenses, payments on account and the basic online filing process.

DIY vs Accountant for Self Assessment: Quick Answer

You can complete your own Self Assessment return if your tax affairs are relatively straightforward and you are comfortable identifying your income, expenses and other information that HMRC requires.

Hiring an accountant may be more appropriate when your affairs are more complicated, you have multiple income sources, you are uncertain about allowable expenses or tax rules, or you want someone to review the figures before submission.

The cheapest option in terms of upfront cost is normally DIY filing. However, price alone does not account for your time, the possibility of mistakes or missed tax reliefs, or the value of professional advice.

What Is a Self Assessment Return?

Self Assessment is HMRC’s system for collecting Income Tax from people whose tax is not fully dealt with automatically through systems such as PAYE.

A Self Assessment tax return reports relevant income, expenses, gains and other information to HM Revenue & Customs so that the correct tax liability can be calculated.

You can normally submit a Self Assessment return online. HMRC also provides paper filing options, although the paper deadline is earlier than the online filing deadline.

Who Needs to File a Self Assessment Tax Return?

Whether you need to file depends on your individual circumstances.

You may need to complete a Self Assessment return if you:

• are self-employed as a sole trader and have sufficient trading income;

• receive taxable income from renting property;

• are a partner in a business partnership;

• receive certain untaxed income;

• have taxable capital gains that need reporting;

• receive certain foreign income;

• have other income or circumstances requiring Self Assessment; or

• have been asked by HMRC to submit a tax return.

Being a limited company director by itself does not automatically mean that you have to complete Self Assessment. Directors should consider their personal income and tax circumstances and whether HMRC requires a return.

If you are uncertain, use HMRC’s current Self Assessment eligibility checker before assuming that you need—or do not need—to file.

Important Self Assessment Deadlines for 2025/26

For the tax year running from 6 April 2025 to 5 April 2026, important dates include:

5 October 2026: Tell HMRC if you need to complete a return for the previous tax year and meet HMRC’s registration conditions.

31 October 2026: Deadline for HMRC to receive most paper Self Assessment returns.

30 December 2026: Relevant deadline if you want HMRC to collect qualifying Self Assessment tax through your PAYE tax code, subject to HMRC’s conditions.

31 January 2027: Online Self Assessment return deadline and the main deadline for paying tax due.

31 July: A second payment deadline can apply where you make payments on account.

Missing the filing or payment deadline can lead to penalties, interest or both, so it is better to deal with your return well before January.

What Happens If You File Your Self Assessment Return Late?

HMRC can charge an initial £100 late-filing penalty if a return that is required is submitted after the deadline.

Further late-filing penalties can arise as the delay continues. After three months, daily penalties of £10 can apply for up to 90 days. Further penalties can apply after six and twelve months.

Late payment can also result in penalties and interest.

This is one reason why leaving your Self Assessment return until the final days of January can be risky. Missing information, login problems or questions about your accounts become much harder to resolve when the deadline is hours away.

How to File a Self Assessment Return Yourself

If you decide that DIY filing is appropriate, the process can be broken down into manageable steps.

1. Check Whether You Need to File

Do not assume that receiving extra income automatically means you need a tax return, or that being employed means you never need one.

Check your circumstances against HMRC’s current requirements.

2. Register for Self Assessment if Necessary

If you need to complete Self Assessment for the first time, you may need to register with HMRC.

Do this early rather than waiting until January.

3. Gather Your Records

Before starting the return, collect the records relevant to your circumstances.

For a sole trader, these might include:

• sales and income records;

• invoices;

• business bank statements;

• receipts;

• details of business expenses;

• PAYE information where relevant;

• pension contribution information;

• savings and investment income; and

• details of any other taxable income.

Landlords may also need records of rental income and eligible property costs.

Good records make both DIY filing and accountant-assisted filing considerably easier.

4. Calculate Your Income and Allowable Expenses

Self-employed taxpayers can deduct qualifying business expenses when calculating taxable profits.

Depending on the business, allowable expenses can potentially include costs relating to office expenses, travel, staff, stock, professional services and other genuine business expenditure.

However, an expense is not automatically allowable simply because money was spent while running a business. Personal expenditure generally cannot be claimed as a business expense.

If an expense has both business and personal use, special treatment may be required.

5. Complete the Relevant Sections of Your Return

Enter your income, expenses and other required information carefully.

The sections you need depend on your circumstances. A sole trader, landlord and person with capital gains may each need different information.

6. Review the Tax Calculation

Before submitting your Self Assessment return, check the figures against your records.

Look particularly for:

• omitted income;

• duplicated figures;

• expenses entered incorrectly;

• missing income sources;

• incorrect personal information; and

• unexpectedly high or low tax calculations.

An unusual result is not necessarily wrong, but it is worth investigating before pressing submit.

7. Submit Your Return and Keep Confirmation

Once you are satisfied that the information is complete, submit the return and retain the submission confirmation with your tax records.

8. Pay the Tax Due

Filing your tax return and paying your tax are separate obligations.

Submitting the return does not mean the tax has automatically been paid. Check the amount due and the payment deadline shown by HMRC.

What Are Payments on Account?

Payments on account frequently surprise first-time Self Assessment taxpayers.

They are advance payments towards a future tax bill and can mean that the amount payable in January is higher than someone expected when looking only at the tax liability for the year just completed.

Payments on account are normally split into two instalments, with payment dates of 31 January and 31 July, where the rules apply.

For example, imagine a sole trader finishes their return expecting to pay tax for the previous year. Their January amount may also include the first payment on account towards the following year’s liability.

That can create a significant cash-flow requirement.

Checking your likely liability well before January gives you more time to budget.

DIY Self Assessment: Advantages

The most obvious advantage of filing your own Self Assessment return is cost. You do not pay an accountant simply to prepare and submit the return.

DIY filing can work particularly well when you have:

• one straightforward source of self-employed income;

• relatively few expenses;

• accurate bookkeeping;

• no complicated property or investment issues; and

• a good understanding of what needs to be reported.

Completing your own return can also give you a detailed understanding of your income and expenses.

DIY Self Assessment: Risks and Disadvantages

DIY filing becomes less attractive as your financial affairs become more complicated.

The main issue is not necessarily completing the online form. The difficult part can be deciding what figures should go into it.

Potential problems include misunderstanding allowable expenses, omitting income, entering figures in the wrong place, failing to consider payments on account or misunderstanding tax treatment.

There is also a time cost.

Spending several evenings researching HMRC guidance, checking records and correcting bookkeeping has an economic value even if no accountant’s invoice is involved.

What Does a Self Assessment Accountant Do?

An accountant can do considerably more than type figures into an online return.

Depending on the service agreed, an accountant may:

• review your financial records;

• identify information needed for the return;

• prepare income and expense calculations;

• check the tax treatment of relevant items;

• prepare your Self Assessment tax return;

• explain your tax calculation;

• identify relevant claims or reliefs based on your circumstances;

• submit the return as your authorised agent; and

• help you plan for upcoming tax payments.

You still need to provide accurate and complete information. Hiring an accountant does not transfer all legal responsibility for your tax affairs to the accountant.

How Much Does a Self Assessment Accountant Cost?

There is no universal UK price for preparing a Self Assessment return.

The fee can depend on factors such as:

• how many income sources you have;

• whether you are self-employed;

• the quality of your bookkeeping;

• whether you have rental properties;

• whether capital gains are involved;

• whether records need correcting;

• how close you are to the filing deadline; and

• whether additional tax advice is required.

Instead of comparing accountants purely by headline price, check exactly what is included.

A low advertised fee may cover a very simple return but cost more once property income, self-employment or additional schedules are added.

Example 1: Sole Trader Self Assessment

Consider a self-employed consultant with one business, straightforward bank transactions and well-organised digital records.

Their DIY process may be relatively manageable:

Business income: £45,000
Allowable business expenses: £9,000
Profit before other relevant adjustments: £36,000

They would use their records to report the appropriate figures and complete any other sections relevant to their personal circumstances.

For someone with clean records and a straightforward business, DIY filing could be reasonable.

Now change the circumstances.

Suppose the same person also has employment income, works partly from home, uses a vehicle for both business and personal journeys, contributes to a pension and has investment income.

The decision about whether to use an accountant becomes less about filling in an online form and more about correctly handling several different tax issues.

Example 2: Property Investor Self Assessment

Consider a landlord receiving rental income from two UK properties.

Their records could include:

Gross rental income: £30,000
Property-related costs: repairs, insurance, agent fees and other relevant expenditure

The landlord needs to determine which costs receive the appropriate tax treatment and accurately report the property income.

Property taxation can involve rules that differ from ordinary self-employed business expenses, so assuming every property-related payment can simply be deducted may result in an incorrect return.

An accountant familiar with property taxation may therefore be useful where the portfolio or financing arrangements are more complicated.

Self Assessment for Landlords

Landlords should pay particular attention to accurate income and expense records.

HMRC guidance states that property income may need to be declared through Self Assessment depending on the amount and circumstances.

Relevant records can include:

• rental statements;

• tenancy-related records;

• letting-agent statements;

• invoices for repairs;

• insurance;

• professional fees; and

• other property expenditure.

Keep property records organised throughout the year rather than trying to reconstruct them shortly before the filing deadline.

Making Tax Digital and Self Assessment

Self Assessment is also undergoing a significant digital change.

From 6 April 2026, Making Tax Digital (MTD) for Income Tax applies to certain sole traders and landlords whose qualifying gross income from self-employment and property exceeded £50,000 in 2024/25.

Those with qualifying income above £30,000 for 2025/26 are due to come into MTD from April 2027, and HMRC’s current timetable extends the requirement to qualifying income above £20,000 for 2026/27 from April 2028.

People within MTD for Income Tax generally need compatible software to maintain digital records, provide quarterly updates and complete their tax reporting requirements.

This makes good digital bookkeeping increasingly important for sole traders and landlords.

Accountant vs DIY: Which Is Right for You?

DIY filing may suit you if your finances are straightforward, your bookkeeping is accurate and you understand the relevant tax rules.

Hiring an accountant may make more sense when:

• you have multiple sources of income;

• your bookkeeping needs attention;

• you own rental property;

• you have disposed of assets;

• you have foreign income;

• your business has grown;

• you are unsure which expenses can be claimed;

• Making Tax Digital applies to you;

• you have received correspondence from HMRC; or

• you simply want professional support before submitting your return.

The decision should be based on complexity, time, confidence and risk, not only the accountant’s fee.

Self Assessment Return Checklist

Use this checklist before starting your return.

Personal and HMRC details

☐ Unique Taxpayer Reference (UTR)
☐ National Insurance number
☐ Government Gateway/HMRC access details
☐ Previous tax return, where relevant

Income records

☐ Self-employment income
☐ Employment information
☐ Rental income
☐ Savings and investment income
☐ Pension income
☐ Foreign income where relevant
☐ Other taxable income

Business records

☐ Sales invoices
☐ Business bank statements
☐ Expense receipts and invoices
☐ Mileage/travel information
☐ Equipment and asset purchases
☐ Professional fees
☐ Other relevant business expenses

Property records

☐ Rental statements
☐ Letting-agent statements
☐ Repair and maintenance invoices
☐ Insurance records
☐ Finance information
☐ Professional fees

Before submitting

☐ Check all income sources
☐ Review expenses
☐ Check personal details
☐ Review the tax calculation
☐ Check whether payments on account apply
☐ Submit before the deadline
☐ Save submission confirmation
☐ Pay HMRC by the applicable deadline

Need Help With Your Self Assessment Return?

Filing your own tax return can be a sensible choice when your circumstances are simple. But when your income, expenses or tax affairs become more complicated, professional support can save time and help you submit an accurate return.

Alpha Accountancy Services provides tailored Self Assessment support for sole traders, freelancers, landlords and individuals with additional sources of income.

Whether you want someone to prepare your entire Self Assessment return or need professional guidance before filing, support can be tailored to your circumstances.

Clients can arrange a virtual consultation, receive remote Self Assessment support nationwide, or speak to the team about in-person accountancy support in Birmingham.

Rather than waiting until the January deadline, getting your records reviewed earlier can give you more time to understand your tax position and prepare for the amount you may need to pay.

Contact Alpha Accountancy Services to discuss your Self Assessment requirements and the filing package that best fits your circumstances.

Frequently Asked Questions About Self Assessment Returns

Can I do my Self Assessment return myself?

Yes. If you need to file and your circumstances are suitable, you can complete your Self Assessment tax return yourself. HMRC provides an online filing service. More complicated tax affairs may make professional advice useful.

Do I need an accountant for Self Assessment?

There is no general requirement to hire an accountant simply because you complete Self Assessment. Many people file their own returns. An accountant can be useful if you have complicated income, property, capital gains, poor records or uncertainty about tax treatment.

When is the Self Assessment deadline?

For the 2025/26 tax year, the normal online filing deadline is 31 January 2027. The normal paper-return deadline is 31 October 2026.

What happens if I miss the Self Assessment deadline?

A late return can trigger an initial £100 filing penalty, with additional penalties potentially applying as the delay continues. Late payment can also result in penalties and interest.

What records do I need for a Self Assessment return?

The records depend on your circumstances. They may include invoices, receipts, bank statements, employment information, rental records, pension information and details of other taxable income.

Can an accountant reduce my Self Assessment tax bill?

An accountant cannot legitimately make tax you owe disappear. However, professional advice can help ensure that relevant allowable expenses, claims and reliefs are considered and that your return reflects the applicable tax rules.

Can an accountant file my Self Assessment return for me?

Yes. An authorised tax agent can prepare and submit a Self Assessment return on your behalf. You still need to provide complete and accurate information and should review the return before it is submitted.

Do landlords need to complete Self Assessment?

Landlords may need to report rental income through Self Assessment depending on their income and circumstances. HMRC currently states that property income above certain thresholds needs to be declared, so check the current rules for your situation.

What are payments on account?

Payments on account are advance payments towards a future Self Assessment bill. Where they apply, payments are normally due in two instalments, on 31 January and 31 July.

Is it better to file Self Assessment early?

Filing early can give you more time to understand how much you owe, budget for the bill and deal with problems before the deadline. Filing early does not normally mean that you have to pay the tax immediately; the applicable payment deadline still applies.