Self-Assessment Deadline Done: What the Budget Means for Your Next Return
By calculatemysalary.co.uk Editorial Team
With the 31 January self-assessment deadline just passed, now is the time to understand how the Autumn Budget 2025 changes affect the 2025/26 tax year and your next return.
The 31 January 2026 Self Assessment deadline for the 2024/25 tax year has just passed. Whether you filed on time or are dealing with a late return, now is a good moment to look ahead at how the Autumn Budget 2025 changes affect the 2025/26 tax year — which will be your next Self Assessment return (due by 31 January 2027, or replaced by Making Tax Digital for some).
What Changed for 2025/26 Returns?
The 2025/26 tax year (6 April 2025 to 5 April 2026) is the last full year before many of the Budget changes take effect. Most of the headline changes from the Autumn Budget apply from April 2026 onwards. However, some changes are already in play:
Already in effect for 2025/26
- Income tax thresholds remain frozen at £12,570 (personal allowance), £50,270 (higher rate), and £125,140 (additional rate).
- Employer NI at 15% with a £5,000 secondary threshold (from April 2025).
- Capital gains tax rates on Business Asset Disposal Relief at the transitional rates.
Taking effect from April 2026 (affecting your 2026/27 return)
- Dividend tax rates increasing to 10.75% (basic) and 35.75% (higher).
- Savings and property income tax rising by 2 percentage points.
- Making Tax Digital mandatory for self-employed and landlords earning over £50,000.
- Homeworking expenses tax relief removed.
If You Missed It
OK, if you missed January 31, HMRC hits you with a £100 penalty straight away. Not because you owe tax, not because you were dishonest — just because you're late. Wait three months longer and you're looking at £10 a day in penalties. Miss six months? That's 5% of whatever tax you owe, or £300, whichever is worse.
Stop reading this and file. Today. The only thing worse than being late is being late and then ignoring it.
Making Tax Digital: The Shift from Annual to Quarterly
If your self-employment or property income exceeds £50,000, the 2025/26 tax year is the last year you will file a traditional Self Assessment return. From April 2026, you must submit quarterly digital updates through MTD-compatible software, with a final declaration replacing the annual return.
This means your 2025/26 return (due by 31 January 2027) will be your last in the current format. Use the remaining months to:
- Choose MTD-compatible software if you have not already.
- Start digital record-keeping for the 2025/26 tax year as practice.
- Sign up for HMRC's pilot programme to test the new process.
Homeworking Expenses Relief — Last Chance
If you work from home and claim the £6 per week flat-rate homeworking deduction (or actual costs), this relief is being removed from 6 April 2026. The 2025/26 tax year is the last year you can claim it.
Make sure to include it on your 2025/26 return if you are eligible. For a basic-rate taxpayer working from home five days a week, the flat-rate claim saves approximately £62 per year in income tax.
Payment on Account
If you owe more than £1,000 in tax through Self Assessment and less than 80% of your tax was collected at source (e.g., through PAYE), you are required to make payments on account. These are advance payments towards your next year's tax bill, each equal to 50% of the previous year's liability.
If your income is changing — for example, because you are expecting lower self-employment income — you can apply to reduce your payments on account. But be aware that HMRC charges interest if you reduce them too far and end up owing more.
Key Dates Ahead
| Date | What Happens |
|---|---|
| 5 April 2026 | End of 2025/26 tax year |
| 6 April 2026 | New dividend, savings and property tax rates take effect; MTD for Income Tax launches |
| 7 August 2026 | First MTD quarterly submission deadline (for Q1: 6 April – 5 July 2026) |
| 31 January 2027 | Self Assessment deadline for 2025/26 (last traditional return for some) |
Review Your Tax Position
If you have just filed your 2024/25 return, you have a clear picture of your current income and tax. Use this as a starting point to:
- Check if you are in scope for MTD from April 2026.
- Review your pension contributions — there is still time to make contributions for the 2025/26 tax year before April.
- Claim any allowances you may have missed (Marriage Allowance, work expenses, professional subscriptions).
Use our UK salary calculator to model your 2025/26 and 2026/27 take-home pay and see how the Budget changes affect your position.
What Actually Changes
Self-assessment used to be routine. This year it's not. From April 6, the rules shift: dividend tax goes up, savings tax follows a year later, homeworking relief vanishes, and MTD launches for anyone earning over £50k. That's a lot of moving pieces.
If you're self-employed or run a property business over that threshold, you're moving from annual tax returns to quarterly reporting. That's not just a filing deadline change — it's a different system. Getting your head around it now means you're not scrambling in September.