May 11
Going self-employed is one of the more liberating decisions you can make as a working professional. You set your own hours, choose your clients, and take control of your income. What comes with that freedom, though, is a set of tax obligations that many newly self-employed people find unexpectedly complicated — particularly when it comes to filing a self-assessment tax return.
Whether you’ve just started out or you’ve been filing returns for years, there’s a good chance there are aspects of self-assessment you’re not making the most of. This guide covers the key points for self-employed individuals in both the UK and Ireland — from what you need to declare and when, to the expenses you can offset and the mistakes that are worth avoiding.
In the UK, you’re generally required to file a self-assessment tax return if you’re self-employed and your trading income exceeds £1,000 in a tax year. That threshold is known as the trading allowance — anything above it needs to be declared.
You’ll also need to file if you have other income that isn’t taxed at source, including rental income above £2,500 per year, dividend income over your dividend allowance, foreign income, or income from savings if it exceeds your savings allowance. Directors of limited companies typically need to file too, even if they draw only a salary — particularly if they receive dividends or have other sources of income.
If you’re unsure whether you need to register for self-assessment, err on the side of caution and check with an adviser early. Registering late can itself attract a penalty.
There are two key filing deadlines for UK self-assessment returns:
The vast majority of people file online, which means the 31 January deadline is the one most commonly missed. It’s also the date by which any tax you owe — plus the first payment on account for the current year — must be paid.
Miss the deadline and you’ll receive an automatic £100 penalty, even if you owe no tax or have already paid everything you owe. Penalties escalate further if returns remain outstanding beyond three and then six months. Interest also accrues on any unpaid tax from the deadline date.
The message is simple: file early, pay on time. The penalties for not doing so are not discretionary — HMRC applies them automatically.
One of the aspects of UK self-assessment that catches people off guard most frequently is the payments on account system. If your tax bill exceeds £1,000 and less than 80% of your tax is collected at source, HMRC requires you to make advance payments towards the following year’s liability.
These payments are due in two instalments: half on 31 January (alongside any balance owed for the previous year) and half on 31 July. Each payment is based on 50% of your previous year’s tax bill.
In practical terms, this means that in your first year of filing, you could face a bill equivalent to 150% of your tax liability — the year’s balance plus the first payment on account. For people who haven’t set money aside for this, it’s a significant financial shock.
The answer is straightforward but requires discipline: set aside a proportion of your income throughout the year — most accountants recommend at least 25–30% for a basic rate taxpayer, more if your income is higher — so you’re never caught out at filing time.
If your income is going to be lower in the current year than the previous one, you can apply to reduce your payments on account accordingly. This is worth doing if your circumstances have changed, as it improves your cash flow position in the short term — just make sure the reduction is realistic, as underpaying can result in interest charges.
As a self-employed individual in the UK, you need to declare all income from your trade or business on your self-assessment return. This includes cash payments, online income, income from multiple clients, and any other revenue arising from your self-employed activities.
You also need to declare any other income you receive that hasn’t been taxed at source — rental income, dividends, bank interest above your savings allowance, income from abroad, and capital gains where they exceed the annual exempt amount.
One area that catches people out is income from platforms — whether you’re selling goods online, renting through short-term let platforms, or providing services through apps. HMRC has been actively working with digital platforms to share data on users’ earnings, which means undeclared income in these areas is increasingly likely to be identified. If you’ve been earning through a platform and haven’t declared it, it’s worth regularising your position sooner rather than later.
Our article on common tax mistakes expats make in the UK, Ireland, and Northern Ireland covers some related points around income disclosure that are equally relevant to UK-based self-employed individuals with varied income sources.
One of the genuine advantages of self-employment from a tax perspective is the ability to deduct business expenses from your income before calculating how much tax you owe. Getting this right can make a meaningful difference to your bill.
Common allowable expenses for self-employed individuals include:
What you cannot claim includes anything with a private or personal element that isn’t exclusively for business, entertaining clients, and the cost of ordinary commuting.
Flat rate simplification schemes are available for some calculations — such as using a fixed mileage rate rather than calculating actual vehicle running costs — which can reduce the record-keeping burden while still giving you a fair deduction. Our digital bookkeeping service helps self-employed clients keep their records structured and accessible throughout the year, making the allowable expenses calculation at return time significantly more straightforward.
Self-employed individuals in the UK pay National Insurance differently from employees. From April 2024, Class 2 NICs were effectively abolished for most self-employed people with profits above the Lower Profits Limit, though those with lower profits can still make voluntary contributions to protect their State Pension entitlement.
Class 4 NICs are still payable at current rates on profits above the Lower Profits Limit, with a reduced rate applying above the Upper Profits Limit. Understanding your NI position is important both for managing your current tax bill and for ensuring you’re accumulating the qualifying years you need for the State Pension.
If you also have employment income alongside your self-employment, the interaction between employee and self-employed NI contributions can create complexity — and potentially mean you overpay NI overall. This is worth reviewing with an adviser.
For self-employed individuals in the Republic of Ireland, the equivalent of UK self-assessment is the annual income tax return, filed through Revenue’s Online Service (ROS). Most self-employed individuals with non-PAYE income above €5,000 are required to file a Form 11.
Ireland operates a Pay and File system, with a single key deadline of 31 October each year for both filing your return and paying any balance of tax owed for the previous year — as well as paying your Preliminary Tax for the current year.
Preliminary Tax is Ireland’s equivalent of the UK’s payments on account. You must pay at least 90% of your final liability for the current year, or 100% of the previous year’s liability (whichever approach you choose), by 31 October. Failing to pay sufficient Preliminary Tax results in interest charges — so planning your cash flow around this deadline is essential.
Self-employed individuals in Ireland pay Income Tax at the standard and higher rates, alongside Universal Social Charge (USC) and Pay Related Social Insurance (PRSI) on self-employed income. The combined burden of these three charges means that effective tax rates for higher-earning self-employed individuals in Ireland are substantial, and proactive planning to make use of available reliefs — pension contributions, capital allowances, business expenses — is important.
The Earned Income Tax Credit is available to self-employed individuals in Ireland as a partial equivalent of the PAYE employee tax credit, though at a lower level. Making sure this is correctly claimed on your return is a basic step that’s easy to overlook.
If you earn income in both the UK and Ireland — which is common for many Northern Ireland-based individuals and for those working cross-border — your tax position can become considerably more complex. Questions of tax residency, which jurisdiction has the primary right to tax your income, and how double taxation relief operates all come into play.
As a general principle, you pay tax where you are resident — but the interaction between UK and Irish rules, and the provisions of the UK–Ireland Double Taxation Agreement, means this isn’t always straightforward in practice.
If you’re managing income, expenses, or tax obligations on both sides of the border, working with cross-border tax advisors who are qualified in both jurisdictions is essential. Our article on UK tax rules for individuals with income in multiple countries explores the broader framework, and our piece on VAT compliance for businesses operating across the UK–Ireland border covers the VAT dimension for those whose self-employed activity also generates a VAT obligation.
If you’re self-employed in the UK and your total income from self-employment and property exceeds £50,000, Making Tax Digital for Income Tax Self Assessment (MTD for ITSA) becomes mandatory from April 2026. From April 2027, the threshold drops to £30,000.
Under MTD for ITSA, you’ll be required to keep digital records and submit quarterly updates to HMRC through compatible software — effectively replacing the annual return with a more frequent, ongoing reporting process.
This represents a significant change in how self-employed people interact with HMRC, and the sooner you start preparing, the less disruptive the transition will be. Our article on Making Tax Digital explained covers the full picture, and our piece on what UK and Irish businesses need to know about Making Tax Digital gives a cross-border perspective. Getting your bookkeeping on to a digital platform now — rather than waiting until you’re required to — gives you time to adapt before the deadline hits.
HMRC has the right to open an enquiry into any self-assessment return within a year of the filing deadline. If they do, they may request information about any aspect of your return — your income figures, your expense claims, your records.
Having well-kept, contemporaneous records is your best defence in any enquiry. If your records are incomplete or your claims are poorly evidenced, you’re in a much weaker position. A good accountant — working with accountants in Armagh or wherever you’re based — will not only help you prepare an accurate return but will also make sure your records are in the kind of order that withstands scrutiny.
In more serious cases — where there are allegations of deliberate underreporting or fraud — a forensic accountant can provide specialist support, including preparing independent expert reports that may be needed in formal proceedings. Our article on what a forensic accountant does and when you need one explains more about when that level of support becomes relevant.
If tax debts have accumulated to the point where they’re creating serious financial pressure on your business or personal finances, our recovery accounts UK specialists can help you understand your options — including how to approach HMRC about a time to pay arrangement and what formal routes are available if the position is more serious.
Many self-employed individuals start out filing their own returns and find it manageable in the early years. As income grows, income sources diversify, expenses become more complex, or cross-border considerations come into play, the value of professional support increases quickly.
A good accountant doesn’t just complete your return — they review your income and expense position proactively, identify reliefs you might be missing, flag upcoming changes to the rules that affect you, and help you plan your cash flow around key payment dates. Read our article on how tax accountants help small businesses for a broader picture of how that ongoing relationship adds value.
Our tax compliance service covers self-assessment for individuals across the UK and Ireland — from straightforward sole traders to more complex cases involving multiple income sources, cross-border activity, or investment income. And for those who also run a business alongside their self-employment, our SME Business Solutions team brings together everything you need in one place.
When do I need to register for self-assessment in the UK?
You should register by 5 October following the end of the tax year in which you became self-employed. So if you started trading in the tax year ending 5 April 2026, you’d need to register by 5 October 2026.
Can I claim expenses I paid for before I formally started trading?
In many cases, yes. Pre-trading expenditure incurred in the seven years before you started trading can be treated as if it were incurred on the first day of trading, provided it would have been an allowable expense had the business already been up and running.
What if I can’t pay my tax bill in full by the deadline?
Contact HMRC before the deadline, not after. HMRC operates a Time to Pay scheme that allows taxpayers to spread payments over a period — but you need to contact them proactively. Ignoring the deadline results in automatic penalties and interest.
Do I need to file a return if I made a loss?
Yes, and it’s worth doing so even if you have no tax to pay. Registering a loss means it can be offset against future profits, reducing your tax bill in subsequent years.
How far back can HMRC investigate my returns?
HMRC can normally go back four years for routine enquiries, six years where careless errors are involved, and up to twenty years in cases of deliberate fraud or evasion. Keeping your records organised and your returns accurate is the best protection.
Self-assessment doesn’t have to be something you dread every January — or every October if you’re in Ireland. With the right records, the right advice, and the right support in place, it becomes a manageable part of running your business rather than an annual panic.
At SCC Chartered Accountants, our team works with self-employed individuals across Northern Ireland, the UK, and Ireland to make sure their returns are accurate, their obligations are met on time, and they’re not paying a penny more tax than they need to.
Get in touch today to find out how we can take care of your self-assessment.
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