As the end of the financial year approaches, many UK business owners and self-employed professionals start focusing on one important task: closing their tax file correctly and on time.
If you already understand the basics of UK tax but want clear and practical guidance for the 2025-26 tax year, this article is written for you. Missing a deadline can lead to penalties and unnecessary stress, even when no tax is actually due. Knowing what needs to be done, and when, helps you stay in control of your finances and avoid last-minute pressure.
This guide explains the key UK tax deadlines for 2025-26, what actions are required at each stage, and why these deadlines matter for your business or self-employed work.
Understanding the UK tax year 2025-26
The UK tax year does not follow the calendar year. It runs from 6 April 2025 to 5 April 2026. Any income you earn and any allowable expenses you claim during this period fall within the 2025-26 tax year.
This applies to sole traders, freelancers, contractors, and business owners who earn income outside PAYE. Understanding the tax year dates is important because all filing and payment deadlines are based on this timeframe.
Who needs to complete a Self-Assessment tax return
Self-Assessment is used to report income that is not fully taxed through PAYE. You will usually need to submit a tax return if you are self-employed, earn freelance or contract income, receive rental income, or have more than one source of income.
Even if your income seems straightforward, HMRC may still require a return. Failing to submit one when required can result in automatic penalties, regardless of whether you owe any tax.
Important UK Tax Deadlines You Must Know for 2025-26
Registering for Self-Assessment
If 2025-26 is your first year of Self-Assessment, you must register with HMRC by 5 October 2025. This deadline applies even if you only traded for part of the year.
For example, if you became self-employed in July 2025, you still need to register by October 2025. Leaving this too late can delay your tax return and create problems later on.
Paper tax return deadline
If you choose to submit a paper tax return, it must reach HMRC by 31 October 2026. Paper filing allows less time for corrections and is now less common, as most taxpayers file online.
Online tax return and payment deadline
For most people, the most important date is 31 January 2027. By this date, you must submit your online tax return for the 2025-26 tax year and pay any tax that is due.
If payments on account apply to you, your first payment will also be due on this date. This often comes as a surprise, especially for those who are new to Self-Assessment.
Payments on account explained
Payments on account usually apply if your previous tax bill was more than £1,000 and less than 80 percent of your tax was collected at source.
You make two advance payments towards your tax bill. The first is due on 31 January 2027 and the second on 31 July 2027. Each payment on account is usually half of the previous year’s Self-Assessment tax bill, after tax already paid at source.
This means your January payment can be significantly higher than expected if you are paying both your final tax bill and your first payment on account at the same time.
VAT deadlines for VAT-registered businesses
If your business is VAT-registered, VAT deadlines are separate from Self-Assessment. Most businesses submit VAT returns quarterly, with payment due one month and seven days after the end of the VAT period.
For example, a VAT quarter ending in March must be submitted and paid by early May. Missing VAT deadlines can lead to penalty points and fines, even when no VAT is owed.
Corporation Tax deadlines for limited companies
Limited companies have different responsibilities from sole traders. In most cases, Corporation Tax must be paid within nine months and one day of the company’s accounting period ending.
Company accounts must also be filed with Companies House, and a Company Tax Return must be submitted to HMRC within twelve months of the accounting period ending. These deadlines are fixed, so forward planning is essential.
Why meeting tax deadlines matters
HMRC applies penalties automatically when deadlines are missed. These can include late filing penalties, daily fines, and interest on unpaid tax. Even being a day late can result in a fine.
HMRC does not accept a lack of awareness as a valid reason for missing deadlines, which is why planning ahead is so important.
Common mistakes at the end of the tax year
Many tax problems arise from simple oversights rather than complex rules. Leaving preparation until January, forgetting payments on account, or missing VAT deadlines are all common issues.
Other frequent problems include claiming expenses without proper records or reporting incorrect income figures. These mistakes can usually be avoided with better organisation during the year.
What to do before closing your tax file
Before the end of the financial year, it is sensible to review all sources of income and ensure that expenses are properly recorded. Bank statements should be checked, and funds set aside for upcoming tax payments.
Taking these steps early makes the filing process smoother and reduces the risk of errors or missed deadlines.
Keeping proper records
Good record-keeping is a legal requirement and makes tax reporting far easier. You should keep invoices, receipts, bank statements, mileage records, VAT documents, and payroll information where relevant.
Records generally need to be kept for at least five years after the submission deadline. Keeping digital records throughout the year can save time and reduce stress at year end.
When professional tax support can help
While some people manage basic tax returns themselves, professional support can be helpful when income increases, tax affairs become more complex, or VAT and Corporation Tax are involved.
Professional advice can help ensure accuracy, reduce risk, and provide reassurance that everything has been handled correctly, particularly when closing your tax file at the end of the year.
Key UK Tax Deadlines 2025-26 and Why They Matter
6 April 2025 is the start of the 2025-26 tax year. From this date, the new tax year begins, income and expenses start counting, and the record-keeping period is set.
By 5 October 2025, you must register for Self-Assessment if you became self-employed or received untaxed income. Late registration can lead to penalties and reduce the time available to prepare your return properly.
From 6 April 2026, Making Tax Digital for Income Tax applies to self-employed individuals and landlords with qualifying income over £50,000. Eligible taxpayers must keep digital records and submit quarterly updates, and non-compliance can lead to penalties.
By 31 October 2026, you must submit your paper Self-Assessment tax return. It is the final deadline for paper filing, and missing it results in automatic late penalties, with less time available to correct errors than online filing.
By 31 January 2027, you must submit your online Self-Assessment tax return. It is the main deadline for most taxpayers, and late filing triggers immediate penalties, even if no tax is due. HMRC charges fines even if no tax is due.
By 31 January 2027, you must pay any tax owed for 2025-26, including any balancing payment due. Paying on time avoids interest and late payment penalties, and the amount must be paid even if it is disputed.
By 31 January 2027, the first payment on account is due if applicable. It counts as advance tax for the next year, often increases the January tax bill, and missing it leads to interest charges.
By 31 July 2027, the second payment on account is due. It completes the advance payments for the next tax year, helps spread tax costs across the year, and late payment adds interest.
By 7 May 2026, you must submit and pay your VAT return if your VAT quarter ends on 31 March 2026. It is the deadline for quarterly VAT reporting, and late submissions attract penalty points, even if no VAT is payable.
By 7 August 2026, you must submit and pay your VAT return if your VAT quarter ends on 30 June 2026. It keeps your VAT account compliant, avoids financial penalties, and supports effective cash-flow planning.
By 7 November 2026, you must submit and pay your VAT return if your VAT quarter ends on 30 September 2026. Failure to meet this deadline affects your VAT compliance record, repeated delays increase penalties, and submission is required under Making Tax Digital rules.
By 7 February 2027, you must submit and pay your VAT return for the October–December quarter. It is the final VAT quarter of the calendar year, penalties apply for late filing or payment, and it must be submitted digitally.
From 6 April 2027, Making Tax Digital for Income Tax begins. Digital record-keeping becomes mandatory for eligible taxpayers, quarterly updates replace annual-only reporting, and preparation is essential to avoid disruption.
By 7 August 2027, the first Making Tax Digital quarterly update is due. It is the first required digital submission under MTD, late submissions can lead to penalties, and it keeps HMRC informed throughout the year.
Stay Compliant and In Control of Your UK Tax Responsibilities
Closing your tax file at the end of the financial year is about more than meeting deadlines. It is about knowing your figures are right, your records are complete, and your obligations to HMRC have been met properly.
By understanding the key UK tax deadlines for 2025-26 and planning ahead, you reduce the risk of penalties, last-minute pressure, and costly mistakes. Whether you are self-employed, running a business, or working in a specific industry, staying organised and informed puts you in control of your tax position and allows you to move into the new financial year with confidence.
Get Expert Help
At Accountancy N Tax, we provide straightforward and cost-effective tax support for UK business owners and self-employed individuals. Our team ensures your Self-Assessment return is prepared correctly, submitted on time, and fully compliant with HMRC, while making sure no allowable reliefs or deductions are missed.
You can contact us on 020 7112 9098, email
info@accountancyntax.co.uk, or visit www.accountancyntax.co.uk to find out how we can support you with your tax affairs.
