SA103F Guide 2025/26: Boxes, Expenses and CIS

SA103F is the full self-employment supplement to your Self Assessment return. This guide uses the 2026 form, covering 6 April 2025 to 5 April 2026. HMRC says to use the full pages if turnover was £90,000 or more, including the equivalent for a full year if you traded for less than a year.

You may also need SA103F below that amount because of accounting-period adjustments, a change of accounting basis, Class 4 National Insurance adjustments or HMRC’s Managing Serious Defaulters programme. Check the official notes for your circumstances; otherwise the short SA103S pages may apply.

Put your invoices, bank records, expense receipts and contractor deduction statements together before opening the return. A folder for each tax year makes it easier to trace a total back to its source. Separate customer payments from money you moved between your own accounts.

For example, a plumber might organise purchases into job materials, vehicle costs and office costs. Keep notes explaining any split between personal and business use. Check the accounting method used in your records before transferring totals.

Business details and accounting dates come first. Turnover goes in box 15; other business income goes in box 16. Expense categories run from boxes 17 to 30, with their total in box 31.

Common trade categories include materials in box 17, subcontractor payments in box 18, vehicle and travel costs in box 20, and office costs in box 23. Disallowable amounts have a separate column.

Net profit or loss appears in boxes 47 or 48. Capital allowances occupy boxes 49 to 57; Annual Investment Allowance is box 49. Follow the notes for adjustments and the final taxable-profit calculation rather than treating accounting profit as your final tax bill.

Box 81 records CIS tax deducted from payments to you by contractors. It is separate from the box for payments you make to subcontractors.

Keep each contractor statement alongside the related invoice and bank receipt. If a figure does not reconcile, resolve the difference before copying it into your return. A simple checklist of statement dates helps you spot a missing month.

Read the current HMRC notes alongside the form, especially for capital allowances, losses and accounting-period changes. The linked official page provides the form and detailed instructions. Ask an accountant about entries you cannot support or adjustments you do not understand.

Work through one category at a time and keep a note of the report or statement behind each total. Review the final return separately from the data-entry session: it is easier to spot a misplaced amount with fresh eyes.

TradeTally brings invoices, receipts and expense records into one place. Use its tax-export workflow to organise figures for your return or share them with your accountant. Review the figures against your own circumstances and HMRC’s notes before submitting.

Start with a few recent invoices and receipts, then check that you can find the supporting record for each total. Good records throughout the year make the year-end review easier.