Updated: 2026-10-24

Self Assessment Workbook 2025-26 UK Excel

Your 31 January 2027 Self Assessment bill in one figure — the 2025-26 balancing payment plus your first 2026-27 payment on account — with every amount next to its box on HMRC's 2025-26 forms.

Preview

What's inside

• Self_Assessment_2025-26_Workbook.xlsx
• Self_Assessment_2025-26_Workbook_EXAMPLE.xlsx
• Start_Here_Guide.pdf

WHY THIS WORKBOOK

• The whole January bill, not just the tax: balancing payment + first payment on account for 2026-27, the 31 July 2027 second payment, both tests that decide whether you need payments on account at all (bill under £1,000, or more than 80% taxed at source), a planner for reducing them (form SA303) and HMRC late interest at 7.75% a year.
• Box numbers from HMRC's own 2025-26 forms: SA103S 2026, SA105 2026 (boxes 5 to 19 are no longer used after April 2025), SA102 and SA100 2026. All 50 box labels in the copy list were checked against the HMRC PDFs.
• Every month in the Ledger sheet: type that month's takings and costs (April 2025 to March 2026) and the SA103S box totals, your bill and your payments update as you type.
• The £1,000 trading and property allowances are tried against your real costs automatically — the workbook works the return out four ways and uses the cheapest.

WHAT IT CALCULATES

• Income tax for England, Wales, Northern Ireland and Scotland (19% / 20% / 21% / 42% / 45% / 48%), Personal Allowance taper over £100,000
• Self-employment profit, Class 4 NIC (6% / 2%), voluntary Class 2
• UK property: rents, costs, 20% mortgage-interest credit (box 44)
• Wages (P60), pensions, savings starting rate and Personal Savings Allowance, dividends (£500 allowance)
• Student Loan Plans 1, 2, 4 and Postgraduate Loan, High Income Child Benefit Charge, Winter Fuel Payment charge, Marriage Allowance, Gift Aid and pension payments (band extension)
• 45p / 25p mileage rate and £10 / £18 / £26 use-of-home flat rate
• Making Tax Digital check: does it start for you on 6 April 2027 (income over £30,000)?
• The 30 December 2026 tax-code option when you owe under £3,000

• Self_Assessment_2025-26_Workbook.xlsx — 9 sheets: Start, You & income, Ledger, Property, Calculation, Payments, HMRC boxes, Checklist, Rates 2025-26
• Self_Assessment_2025-26_Workbook_EXAMPLE.xlsx — the same workbook filled in for a sample freelancer
• Start_Here_Guide.pdf — how to use it, the 2025-26 figures and the key dates

WORKS IN

Microsoft Excel (Windows, Mac, web), Google Sheets (upload, then File → Save as Google Sheets), LibreOffice and Apple Numbers. Money always shows in £, whatever your computer's currency setting.

GOOD TO KNOW

• Every rate is on the Rates sheet with its source (HMRC forms, gov.uk, gov.scot).
• Not covered: capital gains, foreign income, partnerships, trusts, the pension annual allowance charge, losses set against other income.
• A calculator using HMRC's published 2025-26 rates, not tax advice. Check the figures in your HMRC online account before you pay.

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A template you fill in yourself — not legal or tax advice.