Every year, millions of people across the UK put off doing their Self Assessment tax return until the last minute. And every year, it comes back to bite them—late filing penalties, confusion over income, and a scramble to find missing documents. If you’re among the 12.2 million people who need to file a Self Assessment tax return for the 2024–25 tax year, don’t worry. Whether it’s your first time or your fifteenth, this guide breaks things down clearly and simply, so you can get it done without stress.
Who needs to file?
You must file a Self Assessment tax return if you’re self-employed, a partner in a business, or a company director (unless it’s a non-profit). But it’s not just business owners. You also need to file if you:
- Earn over £1,000 from self-employment or side gigs (like freelance work or tutoring).
- Make more than £2,500 from renting out property.
- Get income from savings or investments of £10,000 or more before tax.
- Receive child benefit and your income is over £50,000.
- Are a high earner (£100,000 or more).
- Have untaxed income that HMRC doesn’t know about.
Think of Self Assessment as HMRC’s way of letting you tell them what you owe, because they don’t always know the full picture.
Key dates and deadlines
Let’s clear up the calendar confusion. The tax year for 2024–25 runs from 6 April 2024 to 5 April 2025. Here are the dates you should mark in bold:
- 5 October 2025: Deadline to register for Self Assessment (if you’re filing for the first time).
- 31 October 2025: Deadline for paper tax returns.
- 31 January 2026: Final deadline for online filing and payment of tax owed.
Miss the January deadline, and you’ll face an automatic £100 fine—even if you owe no tax. Wait too long, and penalties accumulate quickly.
What documents do you need?
Before you sit down to file your Self Assessment tax return, get your paperwork sorted. You’ll need:
- Your Unique Taxpayer Reference (UTR) number
- National Insurance number
- Details of all income: employment (P60 or P45), self-employment, dividends, pensions, rental income, etc.
- Business expenses (if self-employed)
- Bank interest, investment income, or crypto gains
- Student loan statements, if applicable
- Contributions to charity or pensions (some are tax-deductible)
A good tip? Create a digital folder on your computer or cloud storage and dump every relevant document into it throughout the year. Come tax time, you’ll thank yourself.
How to actually file
Most people file their Self Assessment tax return online using HMRC’s website or commercial software. If it’s your first time, you’ll need to register first. HMRC will send your UTR by post, which takes approximately 10 days.
The online form is smart, meaning it tailors questions based on your answers. You don’t need to fill out every section—only the ones that apply to you. Still, it’s easy to get tripped up. Many people overreport or overlook allowable expenses, especially those who are self-employed.
If it all feels overwhelming, you can always hire a tax adviser or accountant. They’ll help you claim what you’re entitled to and avoid rookie mistakes.
What if you make a mistake?
Don’t panic. If you file your self assessment tax return and later realise you’ve messed something up, you can amend it within 12 months of the original deadline. So if you filed your 2024–25 return by 31 January 2026, you have until 31 January 2027 to fix it.
If you made a genuine mistake, HMRC is usually reasonable, especially if you’re upfront. But if they think you were careless or deliberately misleading, expect penalties.
Can you pay in instalments?
Yes, you can. If you owe tax and can’t pay it all at once, HMRC offers a Time to Pay arrangement. As long as your debt is under £30,000 and you file on time, you can set up a payment plan online.
But here’s the catch: you need to apply before the due date, and interest still accrues. Don’t leave it too late, or HMRC might take enforcement action.
What’s new for 2025?
There are a few key changes for this year’s return:
- MTD for ITSA pilot: Making Tax Digital for Income Tax Self-Assessment (MTD for ITSA) is still voluntary for most, but more landlords and sole traders are being invited to join the pilot. The full rollout is expected in 2026 for those earning over £50,000, but early adoption might help you get familiar.
- Crypto clarity: HMRC has issued updated guidance on crypto assets. If you’ve dabbled in Bitcoin, Ethereum or NFTs, you must declare capital gains or losses. Ignoring it can land you in hot water.
- Rental reform awareness: Landlords should be aware that new regulations around property standards and licensing could affect what they can claim as expenses. Stay up to date or speak to a property tax expert.
Don’t wait until January
It’s tempting to leave your Self Assessment tax return until the New Year, but doing it early puts you in control. You’ll avoid the annual crash of the HMRC website, get a clearer picture of your tax bill, and even set up a budget to pay it off in chunks.
And if you’re due a refund, you’ll get it sooner. So whether you’re a part-time Uber driver, a full-time freelancer, or a landlord juggling tenants, now’s the perfect time to get on top of your Self Assessment. Gather your documents, check the rules, and get filing.
Because no one wants to start 2026 with a tax headache.
