Self Assessment 2025/26: Deadlines, Records and Preparation Tips
Updated: Sep 14
Self Assessment 2025/26: deadlines, records and preparation tips
If you need to file a Self Assessment return for the tax year ended 5 April 2026, preparing the records early is far easier than rebuilding a year's transactions close to the deadline.
Key 2025/26 Self Assessment dates
5 October 2026: the normal deadline to notify HMRC if you need to register for Self Assessment for 2025/26.
31 October 2026: deadline for most paper Self Assessment returns.
31 January 2027: deadline for most online Self Assessment returns.
31 January 2027: normal deadline to pay the balancing payment for 2025/26 and any first payment on account due for 2026/27.
31 July 2027: second payment on account for 2026/27, where payments on account apply.
If HMRC issues a notice to file later than usual, a different filing deadline can apply. Always follow the deadline shown by HMRC for your own return.
Records to organise before the return
Sales invoices and other evidence of business income.
Purchase invoices and receipts for business expenses.
Business bank and card statements.
Mileage or vehicle records where relevant.
Property income and expense records if you are a landlord.
Details of other taxable income or gains that need to be included on the return.
Self-employed taxpayers generally need to keep their business records for at least five years after the 31 January submission deadline for the relevant tax year. Good records also reduce the need to use estimated or provisional figures.
Making Tax Digital may now apply
Making Tax Digital for Income Tax began from 6 April 2026 for some sole traders and landlords. Whether it applies depends on qualifying income and the relevant start date. See our current Making Tax Digital for Income Tax guide for the phased thresholds and digital-record requirements.
Common year-end problems
Using a personal bank account for everything and being unable to identify business transactions.
Missing invoices or receipts and trying to reconstruct expenditure months later.
Claiming the full amount of a mixed private and business cost without evidence of the business proportion.
Waiting until January before checking whether the bookkeeping is complete.
Forgetting that payments on account can make the first January payment larger than expected.
Self Assessment support in Coventry
InChart Accounting Limited provides Self Assessment tax return support in Coventry together with bookkeeping services for sole traders and small businesses.
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