Self Assessment —
who needs to register and when

Self Assessment is HMRC's system for collecting income tax from people whose tax cannot be handled automatically through PAYE. If you are employed and your only income is your salary, your employer takes care of everything. But for a large and growing number of people — sole traders, company directors, landlords, freelancers, and those with investment income — the responsibility falls on you to register, file, and pay.

Around 12 million people in the UK complete a Self Assessment tax return each year. Many of them do so correctly and on time. Some register late, pay penalties they could have avoided, or miss the system entirely because they did not realise they needed to be in it. This guide sets out clearly who needs to register, when the deadlines fall, and what happens once you are in the system.

Who needs to register?

HMRC requires you to register for Self Assessment if any of the following apply to you in a given tax year:

• You are self-employed as a sole trader and your gross trading income exceeds £1,000. This applies whether the business is full-time, part-time, or run alongside employment.
• You are a company director — particularly where you receive dividends from your company, have income not taxed at source, or your total income exceeds £100,000.
• Your income from property rental exceeds £1,000 in a tax year, before expenses.
• You have untaxed income above £2,500 — such as tips, commission, or casual earnings not captured through payroll.
• Your total income exceeds £100,000, even if all of it is collected through PAYE. At this level, the personal allowance begins to taper and HMRC requires a return to verify the position.
• You receive income from abroad, or you are not domiciled in the UK and have foreign income or gains.
• You need to report a Capital Gain — for example, from selling a second property, shares, or other investments.
• You or your partner received Child Benefit and either of you earned over £60,000 during the year. The High Income Child Benefit Charge applies and must be declared through Self Assessment.
• You received dividends or savings interest above the relevant HMRC allowances — particularly relevant for directors drawing income from a limited company.
• You filed a Self Assessment return in a previous year and HMRC has not told you to stop. Simply stopping without notification can result in penalties for missing returns.

Who does not need to register?

If you have only PAYE income, no other untaxed sources, and your total earnings are below £100,000, it is likely that HMRC handles your tax automatically through your employer and no Self Assessment return is required. The same generally applies if your self-employment income is below the £1,000 trading allowance, or if your savings or dividend income falls within the relevant annual allowances.

The key word is "likely." There are edge cases, and the consequences of missing a filing obligation are more costly than the exercise of checking. If you are in any doubt, the HMRC tool or a brief conversation with an accountant will confirm your position quickly.

Key dates and deadlines

Deadline	What it covers
5 October 2026	Registration deadline for the 2025/26 tax year — if you need to file for the first time, you must register by this date
31 October 2026	Deadline for filing a paper Self Assessment return for 2025/26
31 January 2027	Deadline for filing online and paying any tax owed for 2025/26, plus the first payment on account for 2026/27
31 July 2027	Second payment on account for 2026/27

The registration deadline — 5 October following the end of the relevant tax year — is the one that catches people most often. If you started self-employment or began receiving rental income in the 2025/26 tax year (6 April 2025 to 5 April 2026), you must register with HMRC by 5 October 2026, even if you have not yet calculated how much tax you owe. Missing this deadline can trigger a penalty in its own right, separate from any late filing or late payment charges.

How to register

Registration is done online through HMRC's Government Gateway. For sole traders, the process involves registering as self-employed and creating or logging in to a Government Gateway account. For company directors, registration is slightly different — you register for Self Assessment as an individual, not through the company. HMRC will issue a Unique Taxpayer Reference (UTR) number by post, which typically takes around 10 working days. You will then need to activate Self Assessment within your Government Gateway account before you can file.

One thing to be aware of: registration and filing are separate steps. Receiving your UTR is not the same as completing a return. Once you are registered, you will need to file a return each year until HMRC explicitly tells you that you no longer need to.

Payments on account — a common surprise

Once you have been through Self Assessment once, you may encounter payments on account. These are advance payments towards your next year's tax bill, calculated at half of your previous year's liability. They apply when your Self Assessment tax bill exceeds £1,000 and less than 80% of your tax was collected through PAYE.

In practice, this means that in your first year of Self Assessment, you may face a bill that is 150% of what you expected — the tax owed for the year just ended, plus the first payment on account for the year ahead. This catches a significant number of people unprepared. Planning for this from the outset, by setting aside a proportion of income throughout the year, avoids a difficult cash flow situation in January.

A note on Making Tax Digital

From April 2026, Making Tax Digital for Income Tax (MTD ITSA) has begun rolling out for sole traders and landlords with combined business or property income over £50,000 per year. The £30,000 threshold follows in April 2027. Under MTD, affected taxpayers move from a single annual filing point to quarterly updates submitted through compatible software, with a final year-end declaration replacing the traditional tax return.

If your income is approaching these thresholds, it is worth understanding how MTD changes your obligations — and ensuring your bookkeeping software supports compliant quarterly submissions. HMRC uses existing Self Assessment records to identify who must join the MTD system, so there is no separate registration step if you are already in Self Assessment.

What happens if you miss the deadlines?

HMRC imposes automatic penalties for late registration, late filing, and late payment. A return filed one day late triggers an immediate £100 penalty, regardless of whether any tax is owed. Penalties escalate the longer a return remains outstanding, and interest accrues daily on unpaid tax from the due date. The regime is designed to be unforgiving — which is why acting early, even if the numbers are straightforward, is always the better approach.

This article is for general information purposes and does not constitute tax advice. Tax rules can change and individual circumstances vary. Please speak to a qualified accountant before making financial decisions.