360 Accounts & Bookkeeping Ltd

    Self-Assessment 2025/26 - Why You Should Start Now, Not in January

    ServicesUpdated 26 August 2026

    Overview

    With the 2025/26 Self-Assessment deadline approaching, taxpayers should avoid leaving their tax return until January 2027. Starting early gives sole traders and self-employed individuals more time to gather records, identify allowable expenses, plan for their tax liability and potentially receive refunds sooner. With Making Tax Digital (MTD) for Income Tax also applying from April 2026 to those with qualifying income over £50,000, getting organised early is more important than ever. The blog highlights the key deadlines, tax rates, National Insurance thresholds and penalties, while encouraging taxpayers to take action now rather than risk a last-minute rush or automatic penalties.

    Content Specification

    The 2025/26 Self-Assessment tax return does not need to wait until January. Starting now can make the process easier, reduce the risk of errors and give you more time to plan for any tax you owe. The online filing deadline is 31 January 2027, with an automatic £100 late-filing penalty if you miss it, followed by additional daily and further penalties in certain circumstances. Gathering key records now — including invoices, receipts, bank statements and mileage logs — can help ensure your return is accurate and that you claim all relevant expenses and allowances. With MTD for Income Tax now applying from April 2026 to qualifying individuals with income over £50,000, early preparation can also help you stay ahead of your reporting obligations. Whether you are self-employed, a sole trader or simply need to complete a Self-Assessment return, starting now rather than waiting until January can give you greater control, better tax planning opportunities and less stress.

    Key Figures:

    ·       Personal allowance: £12,570 (2025/26)

    ·       Basic rate: 20% (up to £50,270)

    ·       Higher rate: 40% (£50,271–£125,140)

    ·       Additional rate: 45% (over £125,140)

    ·       Class 4 NIC: 6% on profits £12,570–£50,270; 2% above

    ·       Trading allowance: £1,000

    ·       Online filing deadline: 31 January 2027

    ·       Paper filing deadline: 31 October 2026

    ·       Automatic late penalty: £100

    ·       Daily penalty (after 3 months): £10/day

    ·       Further penalty (after 6 months): £300 or 5% of tax

    Key Points To Remember:

    ·       Start your 2025/26 Self-Assessment now, not in January

    ·       Automatic £100 penalty for missing 31 January 2027 deadline

    ·       MTD for Income Tax applies from April 2026 for incomes over £50,000

    ·       Gather records now: invoices, bank statements, mileage logs, receipts

    ·       Early filing means faster refunds and better tax planning

    Frequently Asked Questions


    When exactly is the Self-Assessment deadline for the 2025/26 tax year?

    The online filing deadline is 31 January 2027. If you file a paper return, it must be submitted earlier, by 31 October 2026. Both dates also apply to paying any tax owed for the year.

    What happens if I miss the 31 January 2027 deadline?

    HMRC issues an automatic £100 penalty immediately, even if you don't owe any tax. After three months, daily penalties of £10 apply (up to £900). After six months, a further penalty of £300 or 5% of the tax due is added, whichever is higher.

    Why should I start my tax return in August instead of waiting until January?

    Starting early means your records are fresher and easier to gather, you have time to claim every allowable expense and allowance, you can plan for any tax bill in advance, and you avoid the rush that leaves many accountants fully booked in January. If you're due a refund, filing early also gets it to you faster.

    What records do I need to prepare my Self-Assessment?

    You'll typically need sales invoices, business and personal bank statements, mileage logs, expense receipts, your P60 or P45 if you also had employed income, records of pension contributions, and any Gift Aid donation receipts.

    Does Making Tax Digital affect my 2025/26 Self-Assessment?

    From April 2026, sole traders and landlords with qualifying income over £50,000 must move to Making Tax Digital for Income Tax, keeping digital records and submitting quarterly updates instead of one annual return. The threshold drops to £30,000 from April 2027, so it's worth checking now whether you'll be affected.

    What are the most common Self-Assessment mistakes?

    The most common mistakes are missing the filing deadline, forgetting to claim allowable business expenses, and failing to declare all income — particularly side hustle earnings, rental income, and bank interest, all of which HMRC can cross-check against third-party data.

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