A plain-English guide to your Self Assessment tax return

Every winter, the same story plays out across the country: millions of people put off their Self Assessment tax return until January, then spend a stressful fortnight hunting for bank statements and receipts. It doesn’t have to be that way. Here’s how Self Assessment actually works, in plain English.

Who needs to file?

Broadly, HMRC expects a Self Assessment return from you if you have income that isn’t already taxed before it reaches you. The most common cases:

• Self-employed people and sole traders — if you work for yourself, this is you.
• Landlords — rental income above HMRC’s reporting thresholds needs declaring.
• Company directors with untaxed income — for example dividends beyond the tax-free allowance.
• Higher earners and people with investment or foreign income — where tax is due beyond what PAYE collects.

If you’re not sure whether you need to file, that’s a five-minute question — ask HMRC, check the tool on GOV.UK, or ask an accountant. Guessing wrongly in either direction costs money: file when you needn’t and you’ve wasted effort; fail to file when you should and penalties follow.

The deadlines that matter

• 5 October — if you’ve never filed before, you must register for Self Assessment by this date, in the tax year after you started receiving the income.
• 31 October — the deadline for paper returns.
• 31 January — the deadline for online returns and for paying the tax you owe. Miss it and an automatic penalty applies, even if you owe nothing.

The trap inside these dates is payments on account: if your tax bill is large enough, HMRC asks you to pay towards next year’s bill in advance, in two instalments — 31 January and 31 July. People budget for the tax they owe, then discover they’re paying roughly half of next year’s bill on top, on the same day. Knowing this in September rather than discovering it in January is worth a great deal of sleep.

What to keep (and for how long)

Good records make the return quicker, cheaper and safer. Through the year, keep:

• Invoices and records of all business income;
• Receipts for business expenses — including the easily forgotten ones like use of home, mileage, software subscriptions and professional fees;
• Bank interest and dividend statements;
• Pension contribution and Gift Aid records — both can reduce your bill;
• P60s and P45s if you also have employment income.

HMRC expects you to keep the records behind your return for years after filing — a simple folder (paper or digital) kept as you go beats an archaeology project every January.

The mistakes I see most often

• Leaving it until January. The return is due 31 January; nothing requires you to wait until then. File in summer and you know your bill months in advance — the deadline becomes a payment date, not a panic date.
• Missing allowable expenses. Legitimate costs go unclaimed every year simply because no one kept the receipt or knew the rule.
• Forgetting payments on account — see above; the most common nasty surprise in personal tax.
• Ignoring HMRC letters. Most are routine. The ones that aren’t get worse with silence. Open them; answer them; or hand them to your accountant.

Where an accountant earns their fee

A good accountant doesn’t just type your numbers into a form. The value is in claiming what you’re entitled to, catching what doesn’t look right before HMRC does, filing on time every time, and telling you in plain English what you owe, when, and why — so tax becomes a known quantity rather than an annual ambush.

Talha Sohail is an ACCA-qualified accountant from Bury, Greater Manchester, writing plain-English notes on tax and accounts for individuals and small businesses. This note is general guidance, not advice on your specific circumstances — tax rules and thresholds change, so check the current figures on GOV.UK or take advice before acting.