A sole trader's year is a shoebox of receipts; the return wants SA103F boxes 17–31 with the disallowable amounts mirrored in boxes 32–46. Between the two sit four traps that £3-ish trackers and free templates reliably ignore. One: the mileage rate is year-aware now — 45p a mile for 2025–26, 55p for 2026–27 (first 10,000 miles per car, 25p after, motorcycles 24p), so every template written before the change silently misstates the biggest expense line a service-trade sole trader has — on this book's shipped example the difference is £850 of deduction. Two: the £1,000 trading allowance is an either/or election — flat £1,000 instead of your actual expenses, never both — and almost nothing in the genre even surfaces the choice. Three: disallowable is a column, not an afterthought — the return asks for each category's total AND its disallowable slice (business entertainment inside the advertising box is the classic). Four: payments on account ambush first-year filers — by 31 January you owe the year's bill PLUS 50% of it again as the first payment toward next year. This workbook carries all four, and its Rates & Sources sheet cites the GOV.UK line each one comes from.

You type where you already live: 250 income rows, 400 expense rows with a category dropdown named exactly as SA103F boxes 17–30 and a disallowable column beside the amount, a 200-row trip log across up to 6 named vehicles with the 10,000-mile threshold applied per vehicle, and a Use of Home sheet that turns hours per month into HMRC's £10/£18/£26 flat-rate bands. The SA103F Map sheet rolls every entry into boxes 17–31 with the 32–46 mirror; the Tax Estimate computes both paths of the trading-allowance election and names the winner, tapers the Personal Allowance above £100,000, runs your profit through the bands of your region — England, Wales & Northern Ireland or Scotland's six bands — adds Class 4 and states your Class 2 position, and prints the payment schedule. On the shipped example — £52,000 of income, 8,500 car miles, a year of logs — the bill is £6,561.10, and the first 31 January asks for £9,841.65: the bill plus a £3,280.55 payment on account, with the same £3,280.55 again due 31 July. That first-year 150% moment is exactly what the sheet warns about.

Both tax years live in one book behind a single switch cell: 2025–26 for the return you file by 31 January 2027, 2026–27 for the records you are keeping right now. Flip it and the mileage rate, the bands, the NIC thresholds and the Class 2 line all follow — the Rates & Sources sheet carries every constant of both years with its value, its GOV.UK (or gov.scot) source document, its URL and the date we captured it, 2026-09-03. A region switch does the same for Scotland: all six Scottish bands of both years are carried and cited, applied to trading profit as Scottish rates actually apply. When rates change again — the next tax year's constants are published each spring — the workbook is rebuilt from a freshly captured, source-cited reference, and your order page always serves the current build: re-downloading is free, as it is for everything we sell.

The whole book was verified against an independent model of the Self Assessment arithmetic before it was allowed to ship: 59 scenarios — every model fixture plus multi-vehicle logs, both election paths, the Personal Allowance taper edge, Class 4 boundary cases, Scottish bands of both years, the 10,000-mile boundary crossed mid-log — each typed through the same yellow input cells you will use, recalculated by LibreOffice, and compared cell by cell: 2,296 assertions, zero mismatches. A mutation self-test proves the harness catches a book that ignores the year switch, miscounts Class 4 or carries a rate typo. The Checks sheet then keeps 13 live self-checks running on YOUR numbers — box 31 equal to the sum of 17–30, disallowable never exceeding its category, the mileage rate matching the year switch, the election applied consistently — so a typo shows up in the file, not in the return.

Honest limits, printed on the Rates & Sources sheet and repeated here. On Making Tax Digital: this file keeps your income and expense records in digital form, and HMRC's own software-choice page says, verbatim, "if you use spreadsheets to record income and expenses, bridging software can connect to them and make your submissions to HMRC" — submission to HMRC happens through bridging software of your choice, not through this file, and we make no compliance claim on its behalf. Out of scope, stated rather than guessed: VAT, CIS deductions, partnerships and limited companies, capital allowances beyond the flat-rate interplay warnings, student loan repayments, the High Income Child Benefit Charge, pension relief, dividend and savings income, and loss carry-back — the sheet names each one. The files are in English; amounts inside the book are in GBP; checkout is in USD like everything on this site.