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If you’ve yet to fill in your tax return for the tax year which ended on 5 April 2025, you risk being slapped with a £100 fine if you don’t get it in by 31 January.
Around 11.5m people in the UK must complete a tax return for the 2024/25 tax year. According to HMRC, as at 5 January 2026, there were 5.65m people who have yet to file their Self Assessment tax returns. Myrtle Lloyd, HMRC’s Chief Customer Officer, said: “New Year is a great time to start afresh. What better way than to ensure your tax affairs are in order for another year than by completing your tax return? If you have yet to start, the clock is ticking. Go to GOV.UK and start today.”
Here, we explain who needs to complete a tax return, how you might be missing out on valuable pension tax relief if you don’t fill one in, what information you’ll need to gather together, and where to go for more help.
Who needs to complete a self-assessment tax return?
You must submit a tax return by 31 January 2026 if in the 2024/25 tax year you were:
- self-employed as a sole trader and you earned more than £1,000
- a partner in a business partnership
- earning more than £100,000
You may need to send in a tax return if you have any other untaxed income such as:
- money from renting out a property, or from tips or commission
- income from savings, investments and dividends that aren’t held in an ISA.
If the untaxed income you receive is less than £2,500, you might not have to complete a tax return but you will still need to contact HMRC on 0300 200 3300 to report it.
If you’ve made a capital gain in the past tax year which is more than the annual exemption for 2024/25 of £3,000, you may also need to submit a tax return. You’ll have a capital gain if you sell, give away, exchange or otherwise dispose of an asset and make a profit or ‘gain’ on what you paid for it.
Check whether you have to use Making Tax Digital for income tax from April 6 this year. Sole traders and landlords with a turnover of more than £50,000 will need to use this, so you’ll need to sign up as soon as possible. Sarah Coles, head of personal finance at Hargreaves Lansdown, said: “Getting started will give you time to get to grips with the software you have to use, and understand the new service. If the change starts to make the process too time-consuming, it gives you a chance to find an accountant to help too.”
Sometimes it can be difficult to know whether you need to submit a tax return or not. If you’re not sure, it’s always worth checking to avoid any potential fines later down the line. You can check on the Gov.uk website or call the HMRC Self Assessment helpline on 0300 200 3310. The staff are usually very helpful, but since January is their busiest month due to the tax return deadline, be prepared to wait a while to speak to an advisor.
Remember too that if you’ve never sent a return before, you’ll need to allow 10 working days to register, so it’s a good idea not to leave things to the last minute. There are different ways to register depending on whether you’re a sole trader, not self-employed or are registering a partner or partnership. You can find information on how to register, along with the required links to enable you to do so here.
Make sure you claim any additional tax relief you are entitled to
Even if none of the above criteria apply to you, you can still choose to fill in a tax return to claim certain income tax reliefs, such as tax relief on pension contributions, charity donations, or on work or business expenses. In some cases, you may not even need to fill in a tax return to claim these reliefs. If you do not otherwise need to fill in a Self Assessment Tax return, you can sometimes make a claim simply by calling HMRC’s Income Tax helpline on 0300 200 3300 with your National Insurance number and details of your pension contributions or charitable payments to hand. HMRC may be able to process these over the phone, but will tell you what you need to do if they are unable to in your specific circumstances.
These reliefs can be very valuable if you are a higher rate tax payer. For example, if you contribute to a personal pension that uses the ‘relief at source’ methodology (as opposed to a ‘net pay arrangement’), your pension provider will usually claim back income tax at 20% and add it to your pension savings, so that for every £80 you contribute, you end up with £100 in your pension. If you pay income tax at the 40% rate however, you’re eligible to claim back an extra 20% (or £20 in the above example) on all your pension contributions – but you will need to claim this back through your tax return or by calling HMRC on 0300 200 3300. Find out more about pension tax relief in our guide How pension tax relief works and about claiming back higher and additional rate relief in our article How do I reclaim higher rate pension tax relief?
Similarly, if you’ve made a donation to charity, an additional 20% in tax relief can go automatically to the charity as long as you completed a Gift Aid declaration when you make the donation. If you’re a higher or additional rate taxpayer, you can then claim back an extra 20% or 25% in tax relief via your tax return or by calling HMRC. Learn more about Gift Aid in our article Giving to charity – how to make your donations go further.
Information you’ll need to complete your return
Gathering all the paperwork you’ll need to complete your return in advance can make the whole process much easier.
If you’re self-employed, you’ll need:
- Your accounts for the year, plus invoices and receipts showing any expenses you’ve incurred.
If you’re employed, you’ll need:
- A P60 form showing your earnings for the year and a P11D form showing any company benefits (such as medical insurance or a car allowance) you received in the year, both of which should have been given to you by your employer. You’ll also need payslips and details of any share options you might have.
If you received any income from savings or investments, you’ll need:
- Any dividend vouchers, as well as interest certificates from banks or building societies. Remember you don’t have to declare any interest from money held in an ISA. If you’ve sold assets such as shares after 30 October 2024 that aren’t held in an ISA, you’ll need to be aware of changed rates of Capital Gains Tax when completing your Self Assessment tax return as it won’t automatically calculate the correct amount of Capital Gains Tax due. You may need to work out an adjustment to the tax automatically calculated using the adjustment calculator on GOV.UK.
If you’re a landlord, you’ll need:
- Rent records and details of any allowable expenses, which are things you need to spend money on when running the property, such as buildings and contents insurance, and maintenance and repairs to the property.
There’s some information you won’t need to include on your 2024/25 tax return. A spokesman for HMRC said: “Customers do not need to include their 2025 Winter Fuel Payment, or Pension Age Winter Heating payment in Scotland, on their tax return for the 2024 to 2025 tax year as payments received in Autumn 2025 will be recovered in the 2025 to 2026 tax return, due by 31 January 2027.”
If the thought of completing a tax return makes you want to weep, it might be worth hiring a chartered accountant to fill it in on your behalf, and if it avoids a potential fine, then it might prove more cost-effective than you think! You can find a qualified chartered accountant in your local area using the Institute of Chartered Accountants in England and Wales’ (ICAEW) directory of chartered accountants.
What happens if you don’t get your tax return in on time
If you’re required to submit a tax return and miss the January 31 deadline, HMRC will automatically issue you with a £100 fine. You’ll be charged this even if you don’t owe any tax.
If your return is three months late, you’ll be charged a daily penalty of £10 per day for up to 90 days (up to a maximum of £900) and if it is six months late, you’ll have to pay a further £300 or 5% of the tax you owe, whichever is greater. After 12 months, there’s another 5% or £300 charge, whichever is greater
There are also additional penalties for late payments of 5% of the tax unpaid at 30 days, 6 months and 12 months. If tax remains unpaid after the deadline, interest will also be charged on the amount owed, in addition to the penalties above.
If you miss the deadline and are hit with a penalty, it may be cancelled or reduced if you have a reasonable excuse, for example you had an unexpected stay in hospital that stopped you sorting out your tax affairs, or a fire, flood or theft prevented you from completing your tax return.
You can download help sheets and guidance to help you complete your tax return here. You can also call HMRC’s self-assessment helpline on 0300 200 3310 if you need advice or help on any sections. Remember, if you’re not sure whether you need to complete one or not, you can check online, or it may be worth calling HMRC to check ahead of the deadline – it will hopefully help avoid any potential fines, and give you peace of mind that you’re not breaking any rules.
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