Who needs to file a Self Assessment return?

Broadly: the self-employed earning over £1,000, business partners, company directors depending on income, landlords, and anyone with significant untaxed income from savings, investments or dividends. If you're unsure, check with HMRC or ask us.

What is the Self Assessment deadline?

31 October for a paper return and 31 January for an online return, which is also when any tax owed for the year must be paid. A second payment on account, if you make them, falls on 31 July.

When do I need to register for Self Assessment?

By 5 October following the end of the tax year you need to report. Registering gives you your Unique Taxpayer Reference (UTR), which can take time to arrive, so don't leave it late.

What are payments on account?

Advance payments towards your next year's tax bill, made in two instalments on 31 January and 31 July, each usually half of your previous bill. In your first year they can land alongside your first full bill, so plan for the cashflow.

What's the penalty for filing late?

An immediate £100 penalty even if you owe no tax, with further daily and percentage penalties over time, plus interest and charges on late payment. All of it is avoidable with a bit of preparation.

Self Assessment: the complete guide

Self Assessment is how HMRC collects tax that isn't taken automatically through PAYE. If you're self-employed, a company director, a landlord, or you have other untaxed income, there's a good chance you need to file a return — and the penalties for missing it are avoidable but real. Here's the whole thing, start to finish.

Do you even need to file?

You generally need to complete a Self Assessment return if any of the following applied in the tax year: you were self-employed as a sole trader earning more than £1,000; you were a partner in a business partnership; you had untaxed income such as rental income, savings, investments or dividends above the relevant thresholds; or you needed to pay the High Income Child Benefit Charge. Being a company director often means filing too, depending on your income. If you're not sure, it's better to check than to assume.

Registering — and the deadline people miss

If it's your first time, you have to register for Self Assessment before you can file. The deadline to register is 5 October following the end of the tax year you need to report — so for income in the 2025/26 tax year, that's 5 October 2026. Registering gives you your Unique Taxpayer Reference (UTR) and access to file, and it can take a little while to come through, so leaving it to the last minute is a common and needless mistake.

The key deadlines

Once you're registered, the dates that matter each year are:

31 October — deadline for a paper tax return.
31 January — deadline for an online tax return, and the date any tax you owe for the year must be paid.
31 July — the second "payment on account" is due, if you make them.

So for the 2025/26 tax year, an online return and the balancing payment are due by 31 January 2027. Most people file online, which gives you the extra three months over the paper deadline.

Payments on account — the surprise for first-timers

If your tax bill is above a certain level, HMRC asks you to pay towards next year's bill in advance, in two instalments — one on 31 January and one on 31 July — each usually half of your previous year's bill. The catch is that in your first year you can face your first full bill and your first payment on account together in January, which can be a nasty cashflow shock if nobody warned you. Planning for it is half the battle.

What you'll need

To fill in the return you'll typically need your UTR and Government Gateway login, records of your self-employed income and allowable expenses, any employment income and P60/P45, details of savings, dividends, rental income, pension contributions and Gift Aid, and any other income. Keeping this organised through the year with decent bookkeeping turns January from a scramble into a formality.

Penalties for filing or paying late

Miss the filing deadline and there's an immediate £100 penalty, even if you owe no tax, with further daily and percentage-based penalties the longer it drags on. Late payment attracts interest and additional charges on top. None of it is worth risking for the sake of a return that, with the right preparation, takes far less time than people fear.

Making Tax Digital is changing this

From April 2026, Making Tax Digital for Income Tax starts to replace the annual return with quarterly digital updates for sole traders and landlords over certain income thresholds. If that's you, the way you report is changing — worth understanding now rather than being caught out.

Get it off your plate

Plenty of people file their own Self Assessment perfectly well. But if it's eating your January, you're not confident you're claiming everything, or your affairs have got more complex, it's exactly the sort of thing we handle for clients — accurately, on time, and without the last-minute panic. Get in touch if you'd like it taken care of.