Self-Assessment is the system HM Revenue & Customs (HMRC) uses to collect Income Tax from individuals whose tax is not fully deducted through PAYE. This includes the self-employed, company directors, business partners, landlords, and anyone with additional untaxed income such as dividends or overseas earnings. If HMRC has issued a notice to file a tax return, you must complete a Self-Assessment return for the relevant tax year.

For the 2024/25 tax year, which runs from 6 April 2024 to 5 April 2025, the deadline for submitting your online Self-Assessment tax return and paying any tax owed is 31 January 2026. This deadline is particularly important as it covers both filing the return and settling any outstanding Income Tax, National Insurance contributions, and the first payment on account for the 2025/26 tax year where applicable.

Missing the 31 January deadline can result in substantial penalties. HMRC applies an automatic £100 fixed penalty as soon as the deadline is missed. If the return remains outstanding after three months, further daily penalties of £10 per day can be charged, up to a maximum of £900. After six months, an additional £300 or five per cent of the tax due may be applied, with a further £300 or five per cent penalty possible if the return is still outstanding after twelve months.

Late payment penalties are separate from filing penalties. If tax remains unpaid 30 days after the 31 January deadline, HMRC charges a penalty of five per cent of the outstanding amount, with further five per cent charges applied at six and twelve months. Interest is also charged daily on any unpaid tax from the day after the payment deadline, meaning the longer the tax goes unpaid, the more it costs.

Many taxpayers encounter difficulties because they leave their return too late, underestimate their tax liability, or miscalculate payments on account. Payments on account are advance payments towards the next year’s tax bill and can increase the total amount due in January, potentially creating cash-flow issues if not planned for.

This is where CMA Accountancy can help. Our experienced team ensures your Self-Assessment tax return is accurate, compliant, and submitted on time. We review your income, expenses, and allowances in detail, helping you to avoid errors and make the most of legitimate tax reliefs. By managing the entire process, we remove the stress of filing and ensure you meet the 31 January 2026 deadline without risking penalties.

CMA Accountancy also provides guidance throughout the year, particularly for those with complex financial affairs or multiple income streams. By keeping your records organised and planning ahead, we help minimise tax liabilities while ensuring full compliance with HMRC regulations.

With penalties and interest escalating quickly for late filing or payment, early preparation is key. Engaging a professional accountant not only saves time and reduces stress but also provides peace of mind that your tax obligations are being handled correctly. As the 31 January 2026 deadline approaches, now is the perfect time to ensure your Self-Assessment is completed accurately and on time with the support of CMA Accountancy.