Filing your first time Self Assessment in 2026? Here's the step-by-step: registering, getting your UTR, the deadlines, and what you'll owe.
The first time you file a Self Assessment tax return, the hardest part isn’t the maths. It’s not knowing the order things happen in, so you don’t realise you needed to register two months ago until you’re staring at a login screen you don’t have the details for. Nearly everyone’s first return is more stressful than it needs to be, purely because of that.
So this is the whole thing laid out in order. If you’re doing your first time Self Assessment in 2026, follow these steps from the top and you’ll avoid the traps that catch most people, especially the one where you leave registration too late to file at all.
Self Assessment is the system HMRC uses to collect income tax from people whose tax isn’t taken automatically through PAYE, which means you tell HMRC what you earned, they tell you what you owe, and you pay it, all by 31 January.
If you’ve only ever been employed, tax just vanished from your payslip before you saw it. Self Assessment puts that job in your hands instead. It’s more admin, but it’s also where the self-employed get to deduct expenses and lower the bill.
Not everyone with a side income has to file. The key number is the £1,000 trading allowance.
If your total self-employed or freelance income for the tax year was £1,000 or less before expenses, you don’t need to register or file at all. Once you go over £1,000 in gross income, you do. Note that’s gross income, not profit, so £1,200 of invoices with £900 of costs still puts you over the line even though you only cleared £300.
You’ll also need to file if you had other untaxed income to declare, such as rental income, dividends above the allowance, or foreign income. But for most first-timers, it’s the £1,000 freelance threshold that brings them in.
This is the step people miss, and it has a hard deadline of its own.
You must register for Self Assessment by 5 October following the end of the tax year you started earning. The 2025/26 tax year ended on 5 April 2026, so if you started freelancing at any point during it, your registration deadline is 5 October 2026. Register at gov.uk/register-for-self-assessment.
Registering isn’t the same as filing. It’s the step that gets you into the system and triggers HMRC to send you the two things you can’t file without: a Unique Taxpayer Reference and a Government Gateway account. Do this early. The most common reason first-timers miss the January deadline is that they left registration until Christmas and the reference number hadn’t arrived in time.
Once you register, HMRC posts you a Unique Taxpayer Reference (UTR), a ten-digit number that’s yours for life. It usually arrives within about 10 working days, or up to 21 if you’re overseas. You’ll also set up or link a Government Gateway user ID, which is how you log in to file.
Keep both somewhere safe. The UTR appears on every piece of correspondence HMRC sends you, and you’ll quote it every year. If it hasn’t turned up two weeks after registering, chase it, because you genuinely cannot submit a return without it.
Filling in the return goes quickly if you’ve got everything to hand, and painfully if you’re hunting for figures as you go. Before you log in, pull together:
If your bookkeeping through the year was a shoebox of receipts, this is the moment it costs you time. Even a simple spreadsheet of income and expenses, kept monthly, turns filing into a half-hour job. A good habit for next year is to log every invoice and receipt the week it happens, and to keep your business money in a separate account so the figures are easy to pull. HMRC also expects you to keep these records for at least five years after the filing deadline, so don’t bin anything once you’ve submitted.
Log in through the Government Gateway and open your Self Assessment return. You’ll work through sections that ask about your self-employment income, your expenses, and any other income. Enter your total income, then your total allowable expenses, and the system calculates your profit.
You can choose between listing expenses in detail or, if your income is under the VAT threshold, entering a single total. As you go, HMRC calculates the tax and National Insurance owed and shows a running figure. Check every number before you submit, then file. You’ll get an on-screen confirmation and a reference, so save it.
The online filing deadline is 31 January 2027 for the 2025/26 tax year. (If you ever choose to file a paper return instead, that deadline is earlier, 31 October.) Do not wait until 31 January itself, because if you hit a snag with your login or a missing figure, there’s no time left to fix it.
Filing and paying are two separate actions, and both are due by 31 January.
Your tax bill will be income tax plus Class 4 National Insurance. For 2026/27, Class 4 NI is charged at 6% on profits between £12,570 and £50,270, and 2% above that. Income tax follows the normal bands: nothing on the first £12,570, then 20% up to £50,270.
Worked example. Say your first year of freelancing gave you £25,000 of profit after expenses. Your personal allowance covers the first £12,570, leaving £12,430 taxable. Income tax at 20% is £2,486. Class 4 NI at 6% on the same £12,430 is £745.80. So you’d owe roughly £3,232 by 31 January.
One thing to brace for: if your bill is over £1,000, HMRC also asks for a first payment on account towards next year, worth half your bill again, on that same 31 January date. On the example above, that’s an extra £1,616, so £4,848 leaving your account in one go. It catches almost every first-timer off guard, so plan for it now.
The mechanics of a first time Self Assessment are steady year to year, but a few 2026/27 figures are worth pinning down. The personal allowance stays frozen at £12,570, the £1,000 trading allowance is unchanged, and the registration deadline of 5 October and filing deadline of 31 January are fixed as ever.
The National Insurance picture is the part that’s quietly better than it was a couple of years ago. Class 4 NI sits at 6%, down from the 9% it used to be before the 2024 cuts, and the flat weekly Class 2 charge is no longer mandatory if your profits are above the small profits threshold, though you can still pay it voluntarily to protect your State Pension record if your profits are low.
What hasn’t improved is the penalty regime. Miss the deadline and it’s an automatic £100, then daily charges after three months, so the value of registering early and filing on time is as high as it’s ever been.
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No. There's a £1,000 trading allowance, so if your total self-employed income for the tax year was £1,000 or less, you don't need to register or file. Once you go over £1,000 in gross income, even by a little, you need to register for Self Assessment and report it.
You must register by 5 October following the end of the tax year you started earning. So if you began self-employment during the 2025/26 tax year, which ended on 5 April 2026, you need to register by 5 October 2026. Register late and you can face a penalty if it causes you to miss the payment deadline.
After you register, HMRC posts your Unique Taxpayer Reference, usually within about 10 working days, or up to 21 if you're abroad. You can't file your return without it, so register early. Leaving registration until January is the single most common reason first-timers miss the deadline.
HMRC charges an automatic £100 penalty the moment you miss the 31 January online deadline, even if you owe no tax. After three months, daily penalties of £10 start adding up, and there are further charges at six and twelve months, plus interest on any unpaid tax. Filing on time, even with an estimate, is always cheaper than filing late.
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A note on financial advice: NetPay UK calculates take-home pay based on official HMRC tax rules. This article reflects rules in force at the time of publication (10 July 2026). Tax rules change. For complex situations, consult a qualified UK accountant or visit gov.uk/income-tax.
