Self Assessment Spreadsheet 2025-26 UK – Tax Return Prep Workbook & Checklist (31 Jan 2027)

A Self Assessment spreadsheet to get your 2025-26 tax return ready for 31 January 2027. Tick through a step-by-step checklist, total your side-hustle income and expenses, and see your figures laid out box by box for the self-employment pages.

First Self Assessment return? Or just dreading January again? Most of the stress is gathering the numbers: what each platform paid you, which receipts count, which rate to use for mileage and where it all goes on the form.

This workbook takes you through it in order, from "do I even need to file?" to paying the bill, to help you get everything together before the 31 January 2027 deadline.

What it does

• Step-by-step checklist: 20 steps from registering and getting your UTR, through gathering income and receipts, to filing and paying, each with its GOV.UK link and a progress bar.

• Key dates that count down, and show "Passed" once gone: registration, the paper and online deadlines, paying through your tax code, payments on account on 31 January and 31 July, and when late penalties kick in.

• Income sorted properly: one row per platform, client or job (eBay, Vinted, Etsy, delivery apps, freelance). Personal items you've sold and income from a job are kept out of your turnover.

• Expenses by HMRC box: pick the box (11 to 19) from a dropdown, add a business-use % for things like your phone, and the totals are done for you.

• Mileage and working from home: built-in helpers use the 2025-26 flat rates (45p then 25p a mile, 24p for motorbikes, and £10 / £18 / £26 a month for working from home).

• Trading allowance or actual expenses? See both profit figures side by side and which is lower (you can only use one).

• Box-by-box summary: your figures laid out in the order of the Self-employment (short) pages, boxes 9 to 28, with plain-English notes.

• Handy checks: short or full pages (the £90,000 turnover line), Class 2 and Class 4 National Insurance flags, and a payments on account planner that shows what's due on 31 January and 31 July.

What's included

• UK-Self-Assessment-Prep-Workbook-2025-26.xlsx: the blank workbook, ready to use.

• UK-Self-Assessment-Prep-Workbook-2025-26-EXAMPLE.xlsx: the same file filled with clearly labelled made-up figures, so you can see how it works.

• A Google Sheets guide. Works in Excel and Google Sheets.

Good to know

• General information only, not tax advice. Check GOV.UK or speak to an accountant or tax adviser about your own situation. It is not an official HMRC form. It helps you gather and organise your figures. It doesn't calculate your tax bill or file anything for you.

• It's for the 2025-26 tax year (6 April 2025 to 5 April 2026), which is the return due by 31 January 2027. Checked on GOV.UK on 28 October 2026.

• It suits sole traders with fairly simple affairs. If you have capital allowances, losses, a partnership or turnover over £90,000, check GOV.UK or an accountant.

• Plain formulas only: no macros, no add-ons, no subscription.

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