Tax return deadline: Expert reveals her ten tips for completing self assessment
The HMRC tax return deadline is fast approaching.
Those who need to complete a self-assessment have until January 31 to complete it and pay the tax they owe.
Sarah Coles, head of personal finance at Hargreaves Lansdown, has some advice for those filing their taxes in the coming days.
He said: “The UK is a nation of last-minute procrastinators hoping to sneak in tax returns at the eleventh hour.
“Almost half of people who were due to file a self-assessment tax return by the end of the month had not completed it by the start of 2026.
“And while there’s nothing wrong with being motivated by a deadline, it increases the risk of something going wrong.
“If you need to complete one and haven’t yet, here are 10 last-minute checks to make sure you avoid major tax filing pitfalls.”
1. First check if you have access to the system
Coles said: “Make sure you have your unique Taxpayer Reference number and can access the Government Gateway immediately.
“If you haven’t signed up for self-assessment, do so now as it will take up to 10 days for your UTR to reach you by mail. If you have not yet registered for the Gateway, it will take up to 10 days for your activation code to reach you. If you have forgotten or lost any of them, you can recover them.
2. Beware of capital gains tax mistakes
The expert explained: “If you sell assets such as shares after October 30, 2024, the system will not automatically calculate the correct amount of capital gains tax you need to pay.
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“Annoyingly, you have to use the settings calculator on the Gov.UK website to make changes to the calculation.”
3. Consider the impact of frozen tax thresholds
“If the salary increase has pushed you over the income tax threshold to pay a higher or additional rate of tax, the extra tax on your income may have been levied through the PAYE system, but this may also mean you need to file a tax return,” Coles said.
“You may need to claim tax on pension contributions or charitable donations, or you may need to pay tax on your savings because your personal savings allowance has been reduced.
4. Consider child allowance
“High-income child benefit costs start at £60,000,” the expert confirmed.
“If your income (or your partner’s income) has since exceeded the threshold and you are receiving child benefit, you will need to repay at least some of it through self-assessment.
“If you tick the box, your debt will be calculated. If you only use it to pay the high-interest child benefit charge, you can pay it via your tax code using the new PAYE digital service.”
5. Don’t forget crypto
“HMRC is reminding people that gains from crypto must be declared for capital gains tax purposes, and you will have to pay tax if your total capital gains exceed your annual allowance,” Coles warned.
“If you have made a loss, you will also need to fill out a tax return if you want to offset it against earnings in future years.”
6. Don’t forget the earnings you make by trading on sites like e-Bay and Vinted
Coles said: “This will include things you have made or bought and sold solely for profit, rather than items from a general liquidation.
“If you are selling for profit you also have a £1,000 allowance, but after that you need to declare this by completing a tax return.
“These sites only had to automatically disclose these profits to HMRC in 2024, but you are responsible for paying this tax.”
7. Don’t rush into retirement.
The expert explained: “This is an area where errors often occur.
“Higher rate taxpayers need to make sure they claim higher rate tax relief if it is not done automatically. For example, in a private pension or SIPP you need to enter the gross value of contributions.
“It’s not just the total of what you paid; it also includes tax relief. For example, if you contributed £800, the gross amount after tax relief is added is £1,000.”
8. Check that you actually paid
“You’d be surprised how many people focus so much on the manager that they forget this part,” Coles said.
“If you owe tax, you must pay it by January 31 at the latest, otherwise you will pay interest and penalties.”
9. What if I can’t pay?
“If you can’t afford your bill, see if you can arrange payment timing by spreading your tax bill over the next few months,” Coles said.
“If you owe £30,000 or less, are within 60 days of the due date and do not already have a payment plan with HMRC, you should be able to do this online.
“It will only be possible to arrange this if HMRC think you can afford it, so it’s not a solution for everyone and there is interest to be paid on the outstanding cash, but it’s a better solution than missing a payment and paying a fine on top of the interest.
10. Check if you need to use Making Tax Digital for income tax from 6 April this year
“Sole traders and landlords with a turnover of more than £50,000 will need to use this, so you will need to register as soon as possible,” he said. “Getting started will give you time to get to grips with the software you need to use and understand the new service. It also gives you the chance to find an accountant to help you if the change starts to make the process too time-consuming.
“While you’re there, consider what your tax return reveals about your finances: If you’ve spent many years digging into details about interest payments, dividends, or profits from stock sales, consider consolidation to simplify things.
“Use your tax return like a checklist: if you’ve had to pay tax on savings or investments, look for ways to shelter them from tax, such as ISAs and pensions.
“Not only does this save you taxes, but it also means you never have to deal with them on tax returns again.”
