Can I do my UK Self Assessment myself without an accountant

Can you do your UK Self Assessment yourself?

Yes — many people complete their UK Self Assessment without using an accountant. HMRC’s online return is designed for individuals to file on their own, and for straightforward situations it can be perfectly manageable. The real question is not “Am I allowed to do it myself?” but “Is my tax position simple enough that doing it myself is sensible, accurate, and worth my time?”

This article will help you decide. It explains what “doing it yourself” actually involves, when it’s usually safe, when an accountant is likely to pay for themselves, and how to reduce the risk of errors, penalties, and stressful surprises.

What Self Assessment is (and what it isn’t)

Self Assessment is the system HMRC uses to collect tax when it can’t be fully handled through PAYE (the tax taken automatically from wages/pensions). You complete a tax return after the end of a tax year to report income, claim allowable expenses and reliefs, and calculate what you owe (or what you’re due back).

Self Assessment isn’t only for “business owners.” You may need it because you’re self-employed, have rental income, receive untaxed income, have capital gains, or because HMRC asks you to complete a return. Importantly, filing a return is a legal declaration — you’re confirming the information is complete and correct to the best of your knowledge.

When doing it yourself is usually realistic

DIY Self Assessment tends to work well when your financial life is easy to describe and easy to evidence. Common examples include:

• Self-employed with a small number of clients and clear income/expenses records.

• Side-hustle income alongside PAYE employment, where you can clearly separate business and personal transactions.

• Simple rental income from one UK property with straightforward costs (agent fees, repairs, insurance, etc.).

• Limited investment/dividend income that is already summarised on statements and not overly complex.

• No unusual tax reliefs, no complicated pension situations, and no cross-border tax issues.

If you can describe your income sources in a few sentences and you have good records, you’re already most of the way there.

When an accountant is more than “nice to have”

There are situations where doing it yourself is still possible, but the cost of getting it wrong rises sharply. You may want professional help if you have any of the following:

• High or multiple income streams (employment + self-employment + rental + investments, etc.).

• Capital Gains Tax complications (selling shares, crypto activity with many transactions, selling a second property, disposing of business assets).

• Foreign income or overseas assets, non-UK domicile questions, or split-year/residency issues.

• Partnership income or complex profit shares.

• CIS (Construction Industry Scheme) deductions and reconciliations, especially if records are messy.

• VAT registration, or you’re nearing thresholds and unsure about what counts.

• Employees, subcontractors, payroll, benefits in kind, or anything that starts to resemble a small company’s admin.

• You’re behind on returns, have received an HMRC enquiry, or you suspect past filings contain mistakes.

In these cases, an accountant isn’t just “filling in boxes.” They’re helping you interpret rules, choose the correct treatment, and defend positions if HMRC asks questions later.

The hidden challenge: it’s not the form — it’s the decisions

HMRC’s online return is mostly a guided questionnaire. The difficulty is not clicking “Next.” The difficulty is deciding what numbers should go into each box and why.

For example:

• Is that cost an allowable business expense, or partly personal?

• Should you claim simplified expenses (where relevant) or actual costs?

• Is a repair a repair — or is it an improvement that needs different treatment?

• Do you need to declare something that feels “small” or “informal”?

• Are you supposed to pay payments on account, and can you reduce them?

If your answers are confident and well-evidenced, DIY is fine. If you find yourself guessing, that’s a sign you either need deeper research (directly from HMRC guidance) or professional advice.

What “doing it yourself” actually involves

To file your Self Assessment yourself, you typically need to:

• Register (if required) and get set up with HMRC online services.

• Collect and reconcile records for income and expenses (and keep supporting evidence).

• Understand what needs reporting (and what doesn’t), including any relevant supplementary pages.

• Complete the online return accurately and on time.

• Pay what you owe by the deadline (or arrange a payment plan if you can’t pay in full).

• Keep records in case HMRC asks questions later.

People often underestimate the “records and reconciliation” step. If you treat your Self Assessment like an annual scramble through bank statements, DIY becomes stressful. If you maintain simple bookkeeping throughout the year, DIY becomes routine.

Key deadlines you need to respect

Deadlines matter because late filing and late payment can trigger penalties and interest. In general terms:

• Tax year ends: 5 April.

• Registering (new to Self Assessment): typically by 5 October following the end of the relevant tax year.

• Online filing deadline: typically 31 January after the tax year ends.

• Payment deadline: typically 31 January (and sometimes 31 July for payments on account).

If you’re filing on your own, build a buffer. Don’t aim for “the evening of the deadline.” Aim for early January (or earlier). That buffer is what protects you from forgotten documents, login issues, or unexpected complications like needing to check figures with a client or letting agent.

Penalties: what can go wrong if you’re late

One of the strongest arguments for filing early is that penalties can apply even if you don’t owe tax. HMRC’s late filing penalties can start with an initial fixed amount and increase the longer the return remains outstanding. Late payment also attracts interest and can trigger additional charges.

This doesn’t mean you should panic — it means you should treat the filing date as a real deadline, not a suggestion. A DIY filer who submits early reduces risk dramatically.

DIY Self Assessment step-by-step (a practical workflow)

1) List every income source you had in the tax year

Start by writing down every income type you received, even if you’re not sure it’s taxable. Examples:

• Employment income (P60, P45, payslips)

• Self-employment invoices/receipts

• Rental income (UK or overseas)

• Dividends, interest, investment income

• Benefits, grants, taxable state support (where applicable)

• Capital disposals (shares, property, crypto)

The goal is completeness. It’s easier to decide “this doesn’t need reporting” than to realise in March that you forgot something that should have been included.

2) Gather the supporting documents before you touch the form

DIY mistakes often happen because someone begins the return with partial information and “fills gaps” later from memory. Instea