The 31st January 2026 deadline is rapidly approaching. An estimated 11 million people will be required to fill in their 2024/25 self-assessment tax return[1], and based on recent trends, more than 1 million will miss the deadline and face automatic penalties.
However, with proper planning and accurate information, you can file confidently and avoid the end of January panic.
Key deadlines to be aware of:
The self-assessment system works retrospectively. For the 2024/25 tax year (6th April 2024 to 5th April 2025), these are your critical dates[2]:
5th October 2025 was the registration deadline for newly self-employed individuals or those with untaxed income. If you missed this, it is important to get in touch with HMRC as quickly as possible.
31st October 2025 was the paper filing deadline, though over an estimated 97% of people now file online.
30th December 2025 mattered if you owe under £3,000 and want HMRC to collect tax through your PAYE code across the next tax year.
31st January 2026 is the main deadline for online filing and payment. Missing this triggers an immediate £100 penalty, even if no tax is owed.
31st July 2026 is when your second payment on account falls due if applicable.
The escalating cost of late payments:
Penalties increase rapidly:
Day 1: Automatic £100 fine, regardless of tax owed.
After 3 months: Daily £10 penalties begin, reaching up to £900 over 90 days.
After 6 months: Additional penalty of 5% of tax due or £300, whichever is greater.
After 12 months: Another 5% or £300 charge.
Late payment penalties are separate. Interest accrues immediately after 31st January 2026, with a 5% penalty after 30 days and further penalties at six and twelve months[3].
Who must file?
Self-assessment applies more broadly than many may realise. Beyond sole traders and business partners, you must file if[4]:
You earned over £100,000 from any source, as high earners may need to repay personal allowance
You received rental income exceeding £2,500 before expenses, including foreign or holiday properties
You are a company director receiving dividends or benefits
Your savings, investments, or dividends generated more than £10,000 in income
You sold assets like shares or second properties requiring Capital Gains Tax reporting
You or your partner earns over £60,000 while receiving Child Benefit, triggering the High Income Child Benefit Charge
It’s important not to leave filing until the last minute. You can find further information on Self-Assessment Tax Returns on the HMRC website. Start gathering your records now and register now with HMRC to complete your return online to ensure a stress-free submission, and please reach out to a financial planner if you require any assistance.
Written by Peter Hope, Financial Planner
Acumen Financial Planning Ltd is authorised and regulated by the FCA, FRN 218745. The content within this article is for information purposes only and should not be regarded as advice.
[1] 11.5 million file Self Assessment by 31 January deadline – GOV.UK
[2] Self Assessment tax returns: Deadlines – GOV.UK
[3] Self Assessment tax returns: Penalties – GOV.UK
[4] Self Assessment tax returns: Who must send a tax return – GOV.UK