Do You Need to File a Tax Return? The Question Worth Asking Before January

More PAYE employees need to file than realise. And some of those who do are leaving significant money unclaimed.

10 min read · Updated June 2026

Most people who file a Self Assessment tax return do so because something prompted them. A letter from HMRC. A conversation with an accountant. A realisation that they had been missing a relief for several years. Rarely does anyone file because they proactively identified the obligation and got ahead of it.

This matters because late filing penalties are automatic, fixed, and indifferent to the reason you did not know you needed to file. The first penalty is £100, applied the day after the deadline whether you owe tax or not. It escalates from there. And the deadline — 31 January for online returns — is not negotiable.

The more useful question is not “what happens if I file late.” It is “do I need to file at all?”

The penalty for filing late is fixed and automatic. The reward for filing correctly is sometimes substantial. Both are worth knowing about before January.

The Triggers

HMRC requires a Self Assessment return if any of the following applied in the tax year. This list is not exhaustive but covers the most common situations.

You were self-employed with trading income above £1,000. This includes freelance income, consulting, and any business activity conducted in your own name.

You had rental income above £2,500 after allowable expenses.

Your Adjusted Net Income exceeded £100,000. This is the most commonly missed trigger. A PAYE employee earning £105,000, with no other income, no rental property, and no side work, is still required to file. HMRC does not always write to remind you. The obligation exists regardless.

You or your partner received Child Benefit and either of you had income above £60,000. The High Income Child Benefit Charge is collected through Self Assessment. If you have been receiving Child Benefit without filing a return, you may have an outstanding liability.

You are a company director. With some limited exceptions.

You want to claim a relief that PAYE does not collect. This includes higher rate or additional rate relief on personal pension contributions made through Relief at Source, Gift Aid relief beyond the basic rate, and professional expenses not reimbursed by your employer.

The money being left behind:

A higher rate taxpayer contributing £10,000 per year to a personal SIPP does not receive the full tax relief automatically. The provider claims 20% from HMRC. The additional 20% — worth £2,000 per year — must be claimed through Self Assessment.

Not filing does not mean you do not owe this relief. It means HMRC keeps it.

Over ten years, unclaimed SIPP relief at this level amounts to £20,000. The cost of filing a return is measured in hours.

The Deadlines

5 October: Register for Self Assessment by this date in the year following the tax year in question. For 2025/26 (ending 5 April 2026): register by 5 October 2026.

31 October: Deadline for paper returns.

31 January: Deadline for online returns and payment of any tax owed.

The 31 January deadline covers both the return and the tax. If you have tax to pay, it is due on the same date as the return — not separately, not later. Interest begins accruing from 1 February on unpaid amounts.

What the Return Actually Involves

For most PAYE employees who trigger the filing obligation through the £100,000 threshold, the return is considerably less daunting than its reputation suggests. HMRC pre-populates the return with employment income from employer submissions and bank interest from financial institutions. In many cases, the process involves confirming the pre-populated data, adding any deductions not captured through PAYE, and submitting.

The complexity scales with complexity of income. Multiple income sources, rental properties, self-employment, and significant investment income all require more careful attention. For straightforward PAYE-plus-pension situations, the return is a manageable annual task.

The return is also where you formally claim any adjustments to your tax position that HMRC has not made automatically: additional pension relief, Gift Aid deductions from ANI, professional expenses. For some people, the return results in a rebate rather than a bill.

The Bottom Line

If any of the triggers listed above apply, register and file. The penalty for not filing is certain. The potential rebate for filing is sometimes significant. And the administrative effort — particularly for a PAYE employee with straightforward circumstances — is a morning, not a crisis.

Important: This article is for informational purposes only and does not constitute financial or tax advice. Based on 2026/27 HMRC rates which are subject to change. Individual circumstances vary. Seek independent advice from a qualified financial adviser before making any financial decisions. When you invest, your capital is at risk. WageLab is not FCA regulated.

Use the WageLab calculator to see how these tax rules apply to your specific circumstances.

WageLab is not FCA regulated and does not provide financial advice. This article is for informational purposes only. Full article content coming soon.