Put simply, Self Assessment is HMRC’s way of collecting tax from people whose income isn’t automatically taxed. If you’re employed, your employer sorts most of it through PAYE. But if you’re self‑employed, have a side business, rent out a property, or earn over £100,000, you’re expected to tell HMRC what you’ve made and what tax you owe.

We remember a client who came to us years ago – a freelance graphic designer who’d been working for three years without filing anything. She thought HMRC would just “know” about her income. They don’t. It’s on you to report it. Once she got into the rhythm of doing her return each year, she said it became just another part of her routine, like renewing her car insurance.

who needs to file a self assessment tax return UK

You might be surprised how many people end up needing to file. It’s not just the self‑employed. The list includes:

• Anyone who’s self‑employed and earned more than £1,000 in the tax year (that’s your gross income, not profit)
• Partners in a business partnership – even if the business made a loss
• Company directors, unless your company is dormant or a non-profit
• People with savings or investment income over £10,000
• Anyone earning over £100,000 – even if you’re on payroll
• Those with foreign income that hasn’t been taxed in the UK
• If you sold a property and made a capital gain in 2025/26, you might need to report it separately, but sometimes it’s done through a return

The simplest way to be sure? HMRC has an online checker. But if you’re still unsure, drop us a line – we deal with this every day.

how to do self employed tax return

If you’re self‑employed, the tax return basically wants to know two things: how much money came into your business, and what you spent to earn it. You don’t have to upload every receipt – just the final numbers. The main bits are:

• Turnover: all the money your business took in before any expenses
• Allowable expenses: what you paid out for things like stock, travel, marketing, or a new laptop
• Profit: turnover minus expenses – this is the figure HMRC actually taxes

If your self-employed income is under £1,000, you’re covered by the trading allowance and don’t need to register. But if it’s over, you’re in the system and must file each year – even if your profit is tiny.

government gateway self assessment registration

You can’t file online without a Government Gateway account. If you’ve filed before, you just log in. If you’re new, you need to register. And here’s the thing: HMRC sends an UTR by post. That takes time – often a week or more.

One that sticks in our memory is a bloke who rang us mid‑January, proper panic in his voice. He’d left his tax return to the last minute and only then realised he’d never signed up for online filing. We had to explain that the UTR wouldn’t arrive before the 31st.

In the end we got a paper return submitted as a stopgap, but the paper deadline had already passed, so he still copped a late penalty. Honestly, it’s a situation you want to avoid.

The steps are straightforward:

1. Go to GOV.UK and search “register for Self Assessment”
2. Have your National Insurance number and address ready
3. HMRC posts you an UTR – allow 7 to 10 working days
4. When the code finally lands on your doormat, head back online, enter it, and finish setting up your account

self assessment tax return deadline uk

HMRC don’t shift these dates – they’re set in stone. For the 2025/26 tax year (6 April 2025 to 5 April 2026), here’s what you need to keep in mind:

Everyone focuses on 31 January, and yes, that’s the big one. But the 5 October registration date is just as important if you’re new. Miss that, and you might not get your activation code in time for January. We’ve seen it happen more times than we’d like.

If you owe tax, 31 January is also when HMRC want their money. You can pay by bank transfer, debit card, or through your accounting software. If you can’t pay in full, you can set up a payment plan – but you need to arrange that before the deadline, not after.

hmrc self assessment help and contact options

HMRC do have helplines, but anyone who’s tried calling in January knows it can be a long wait. Their online chat is often quicker for simple queries. And their website has guides on almost everything – claiming expenses, what to do if you can’t pay, how to amend a return.

Some of the things people search for most often:

• Working from home expenses – there’s a flat rate you can claim without receipts
• What counts as an allowable expense for self‑employed people
• How to report rental income from a second property
• Setting up a payment plan if you can’t pay your tax bill on time

Something we say to clients all the time: if you’re not sure, just ask. Guessing and getting it wrong can trigger an HMRC enquiry, and even if you’ve done nothing wrong, that’s a headache you don’t need.