January 2026: Key Self Assessment Tax Deadlines You Must Not Miss
January is one of the most important months in the UK tax calendar, especially for anyone who files a Self Assessment tax return. As January 2026 approaches, taxpayers need to be aware of several critical deadlines that can have serious financial consequences if missed.
Below is a breakdown of what’s due, when it’s due, and why it matters.
31 January 2026: A Crucial Deadline for Self Assessment
31 January 2026 is the main Self Assessment deadline and one of the busiest dates for HMRC each year. On this day, three important obligations fall due:
1. Deadline for Filing Online Self Assessment Tax Returns
If you’re required to complete a Self Assessment tax return, this is the final date to submit your online return for the 2024/25 tax year.
Missing this deadline can trigger automatic penalties, even if you don’t owe any tax.
2. Payment Deadline for Tax Owed
Any tax owed for the 2024/25 tax year must be paid in full by this date. This includes:
Income Tax
Capital Gains Tax (if reported through Self Assessment)
Student loan repayments collected via Self Assessment
Failure to pay on time can lead to interest charges and late payment penalties.
3. First Payment on Account for the 2025/26 Tax Year
If you make Payments on Account, you’ll also need to pay the first instalment toward your 2025/26 tax bill on 31 January 2026.
This payment is usually 50% of the previous year’s tax bill and is paid in advance to help spread the cost of your tax over the year.
1 February 2026: Penalties and Interest Begin
From 1 February 2026, HMRC will start charging:
Late filing penalties if your tax return was not submitted on time
Interest on unpaid tax, calculated daily until the balance is cleared
The initial late filing penalty is £100, even if no tax is owed. Additional penalties can apply the longer the delay continues.
Why Planning Ahead Matters
January deadlines often catch people out, especially after the Christmas period. Leaving things until the last minute can result in:
Stress and rushed submissions
Cash flow issues
Avoidable penalties and interest
Planning ahead, setting reminders, and working with an accountant can help ensure everything is filed and paid on time.
How JSB Accountants Can Help
Navigating January’s tax deadlines doesn’t have to be stressful. Together with JSB Accountants, you can approach Self Assessment with confidence, clarity, and peace of mind.
Self Assessment Preparation and Filing
JSB Accountants work together with you to prepare and submit your 2024/25 Self Assessment tax return, ensuring it is accurate, compliant, and filed on time.
Clear and Accurate Tax Calculations
Understanding your tax bill—especially when Payments on Account apply—can be confusing. Together, JSB Accountants will clearly explain:
Your total tax liability
Payments on Account due for 2025/26
Whether future payments can be reduced
This means no surprises and better financial planning.
Payment Planning and Support
Meeting the 31 January payment deadline can be challenging. Working together, JSB Accountants can help you:
Plan and budget for tax payments
Explore Time to Pay arrangements with HMRC where appropriate
Manage cash flow more effectively
Ongoing Advice and Peace of Mind
Tax rules change, but you don’t have to keep up with them alone. Together with JSB Accountants, you’ll receive ongoing support, reminders, and expert guidance throughout the year.
Final Thoughts
January 2026 is a key month for Self Assessment taxpayers. With filing deadlines, payment obligations, and advance payments all due on 31 January, preparation is essential. Missing these dates can be costly, but staying organised, and working together with JSB Accountants, can make the process far smoother.
If you’re unsure what you owe or whether Payments on Account apply to you, seeking advice well before the deadline can make all the difference.
As a family-run company, we pride ourselves on providing a bespoke service tailored to your particular needs.
Above all, our objective is to save you time, money and effort in managing your accounts, leaving you free to focus on building your business.
Remember, you’re not alone, we’re always here to help if you have an accounts problem or query
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