Guides
The rules behind the spreadsheets, with the numbers shown.
Each guide takes one rule, shows the current figures with their gov.uk source, and works through an example in real pounds. Nothing here is tax advice; it's the working.
Sole traders
Sole traders · 2025/26 and 2026/27
HMRC mileage rates for 2025/26 and 2026/27: 45p becomes 55p
The flat rate per business mile changed on 6 April 2026. The date of each journey decides which rate applies, and the bookkeeping spreadsheet picks it for you.
Sole traders · 2025/26 and 2026/27
Making Tax Digital for Income Tax: are you in from April 2026, 2027 or 2028?
MTD adds four quarterly updates to the year, and the tax return itself is filed through software. The threshold that decides when you join is your gross income two tax years earlier.
Sole traders · 2025/26 and 2026/27
SA103 explained: which box each expense goes in
Every expense you record has a box waiting for it on the self-employment pages. Once you know the fourteen expense boxes, the tax return is mostly copying totals across.
Sole traders · 2025/26 and 2026/27
Trading allowance or actual expenses: which should you claim?
The £1,000 trading allowance replaces your expenses; it doesn't sit on top of them. If your costs are under £1,000 the allowance wins, and more people are in that position than expect to be.
Sole traders · 2025/26 and 2026/27
Working from home as a sole trader: the simplified flat rates
If you work from home 25 hours a month or more, HMRC lets you claim a flat monthly amount instead of splitting the gas bill. It's small, but it's simple, and it stacks up over a year.