Self Assessment Spreadsheet UK 2025-26 | SA103 + Tax Guide

Log it once, map it to the right SA103 box, and see your real January bill — including the Payments on Account most first-timers never see coming.

SA Sorted is a self-employed tax spreadsheet for the UK 2025-26 Self Assessment (the return due online 31 January 2027), for sole traders and employed side-hustlers.

You get:

– A 9-tab Excel/Google Sheets workbook (no macros): Income, Expense and Mileage logs with enforced category dropdowns — expense categories are the actual 2025-26 SA103F box names.

– An SA103 Mapper computing your figure for every box on both the short and full forms, with the £90,000 which-form test. At least one popular Self Assessment spreadsheet ships with wrong box numbers; ours were verified against the 2025-26 forms on gov.uk, and the source table proving it is in your download.

– A Tax & NI Estimate: personal-allowance taper, Class 2/4 National Insurance, trading allowance vs actual expenses side by side with the winner named, PAYE + side-hustle stacking, and a Payments on Account forecaster showing your estimated 31 January and 31 July totals.

– Scottish income tax built in — one toggle, all six 2025-26 bands. Mileage at the correct 45p rate for 2025-26 (the 55p rate only starts April 2026).

– A Health Check panel: every log reconciled to £0 unmatched, missing-data counters, and a 9-item pre-filing checklist.

– A 3,086-word Filing Guide (print-ready PDF): registration, form choice, box-by-box walkthrough, deadlines, penalties, Payments on Account in full — every fact cited to gov.uk, checked August 2026, with the full claim-by-claim source table included. Plus Google Sheets import instructions.

Straight answers on what it isn't: It does not file with HMRC — you copy the verified figures into HMRC's free online return yourself. Tax figures are ESTIMATES: student loans, CGT, savings/dividends and the High Income Child Benefit Charge are out of scope (the guide lists the exact exclusions).

Under the £1,000 filing threshold as an online seller? Seller's Ledger UK (£9): britdesign.gumroad.com/l/ifdzgj. Over £50,000 (or £30,000 from 2027) and moving to quarterly MTD? MTD Ready (£14): britdesign.gumroad.com/l/sycuwa.

Built with AI assistance and human-directed research; every tax fact is checked against the cited official gov.uk/HMRC source — the claim-by-claim source table ships in your download.

Not tax, accounting, or financial advice. Support: mybritdesign@gmail.com