Who needs to file a Self Assessment tax return

If you work for yourself, the chances are you’ll need to file a Self Assessment tax return each year. HMRC expects one from anyone who is a sole trader earning more than £1,000 in a tax year, partners in a business partnership, and many company directors. Landlords with rental income, people with significant savings or dividend income outside their personal allowance, and those with untaxed income from side projects often need to file too.

The £1,000 trading allowance means you can earn up to that amount from occasional freelancing or selling without needing to declare it. Cross that threshold, though, and you’re in the system. It’s worth checking your position early rather than assuming you’re exempt, because the penalties for not filing are automatic and unemotional.

One common trap: taking on a few weeks of freelance work alongside a PAYE job can push you into Self Assessment for the first time. If in doubt, use HMRC’s online checker or speak to an accountant before the deadline sneaks up.

Key dates and deadlines you cannot ignore

The tax year runs from 6 April to 5 April. If you need to register for Self Assessment, you must tell HMRC by 5 October following the end of the tax year in which you started working for yourself. Register too late and you may face a failure to notify penalty, even if no tax is ultimately owed.

• 5 October: deadline to register for Self Assessment if you’re new to it.
• 31 October: deadline for filing a paper return.
• 30 December: deadline for filing online if you want any tax owed (under £3,000) collected through your PAYE code.
• 31 January: deadline for filing online and paying the tax you owe.
• 31 July: second payment on account, if you make them.

Late filing triggers an immediate £100 penalty. After three months, daily penalties of £10 start, up to a maximum of £900. At six and twelve months, further penalties of £300 or 5% of the tax due apply, whichever is higher. Late payment adds interest and its own 5% surcharges at 30 days, six months and twelve months.

Keeping records that stand up to scrutiny

Good record-keeping is the single best defence against a stressful tax return. You must keep business records for at least five years after the 31 January filing deadline. That includes invoices, receipts, bank statements, mileage logs, contracts and details of any stock or equipment purchases.

Digital records are fine — HMRC accepts scanned receipts and app-based bookkeeping. What matters is that you can show where every figure came from if HMRC asks. A separate business bank account, even a basic one, makes this dramatically easier and prevents personal and business spending from blurring together. Sort receipts monthly rather than stuffing them in a drawer for January.

If you use accounting software, make sure the categories you assign match what you’ll declare. Mis-labelling a personal Tesco shop as “office supplies” is the kind of thing that unravels an otherwise clean return.

What you can legitimately claim as expenses

Allowable expenses are costs incurred “wholly and exclusively” for your business. Claim too little and you overpay tax; claim things that are clearly personal and you invite questions.

• Office and admin: stationery, postage, phone and internet business proportion, software subscriptions.
• Travel: business mileage at 45p per mile for the first 10,000 miles, then 25p. Train fares and parking for client visits.
• Clothing: uniforms and protective gear only — ordinary suits don’t count.
• Professional fees: accountancy, legal costs, professional body subscriptions, indemnity insurance.
• Marketing: website hosting, advertising, business cards, design work.
• Training: courses that update skills in your existing trade, not training for an entirely new career.

If you work from home, you can use HMRC’s simplified expenses — a flat rate of £10 to £26 per month depending on hours worked — or calculate a reasonable proportion of actual bills.

Payments on account and cash flow planning

Once your tax bill exceeds £1,000, HMRC usually asks for payments on account. Each is half of your previous year’s bill (less tax already deducted at source), due on 31 January and 31 July. This catches many newly self-employed people off guard, because it means the first January payment can effectively be 150% of the year’s liability.

Put aside a percentage of every invoice — 25% to 30% is a sensible starting point — into a separate savings account. If your income drops sharply, you can ask HMRC to reduce your payments on account, but be cautious: if you reduce them too far and still owe the tax, interest applies.

Getting support and staying ahead

You don’t have to do this alone. An accountant who understands sole traders can often save more than their fee through accurate expense claims and planning. If your affairs are simple, HMRC’s own guidance and free online tools may be enough.

The golden rule is to treat the deadline as a recurring event, not a surprise. File early, pay what you can when you can, and keep talking to HMRC if money is tight — they can arrange instalments. A calm, well-organised approach to your tax return is one of the most valuable habits a self-employed person can build.