SA103 expense categories explained
If you are self-employed, your business expenses end up on the SA103 pages of your Self Assessment return, sorted under HMRC's own headings. Knowing which heading each cost belongs to, and which costs are not deductible at all, is most of the battle of doing your own books. This guide walks through the categories with examples.
SA103S or SA103F?
There are two versions of the self-employment pages. SA103S (short) is for straightforward businesses with turnover below the VAT registration threshold (£90,000); it lets you report a single total for expenses if you prefer. SA103F (full) is required above that threshold or where your affairs are more complex, and it itemises expenses in boxes 17 to 30. Even if you qualify for the short form, categorising your expenses properly is worth doing: Making Tax Digital quarterly updates use the same headings, and category-level records make errors visible.
The expense boxes, one by one
The headings below are taken from the SA103F form for the 2025/26 tax year. The disallowable column matters: some costs are entered here but then added back in boxes 32 to 45, so they never actually reduce your tax.
| Box | Heading | Typical examples | Watch out for |
|---|---|---|---|
| 17 | Cost of goods bought for resale or goods used | Stock, raw materials, direct costs | Goods taken for personal use are disallowable |
| 18 | Construction industry: payments to subcontractors | CIS subcontractor payments | Keep CIS statements |
| 19 | Wages, salaries and other staff costs | Employee wages, employer NI, pensions | Your own drawings are not wages and are not deductible |
| 20 | Car, van and travel expenses | Fuel, insurance, repairs, fares, mileage rate | Home-to-work commuting is not business travel |
| 21 | Rent, rates, power and insurance costs | Business premises rent, utilities, insurance | Use-of-home claims need a reasonable basis or the flat rate |
| 22 | Repairs and maintenance of property and equipment | Fixing tools, servicing equipment | Improvements (not repairs) are capital, not expenses |
| 23 | Phone, fax, stationery and other office costs | Mobile bills, software subscriptions, postage | Apportion mixed personal/business use |
| 24 | Advertising and business entertainment costs | Ads, website, marketing | Business entertainment is entered here but is disallowable |
| 25 | Interest on bank and other loans | Business loan interest | Only the interest, not capital repayments |
| 26 | Bank, credit card and other financial charges | Account fees, card processing fees | |
| 27 | Irrecoverable debts written off | Invoices you will genuinely never collect | Must have been included in turnover first |
| 28 | Accountancy, legal and other professional fees | Accountant, solicitor, professional subscriptions | Fees for buying capital assets are capital |
| 29 | Depreciation and loss or profit on sale of assets | Depreciation in your accounts | Always disallowable; capital allowances are claimed instead |
| 30 | Other business expenses | Anything allowable that fits nowhere else | Keep this small; big "other" totals attract questions |
Simplified expenses
Instead of actual costs, sole traders can use flat rates for certain expenses:
- Vehicles: from 6 April 2026, 55p per mile for the first 10,000 business miles in cars and goods vehicles (45p before that date), then 25p per mile; motorcycles 24p per mile. Using the mileage rate replaces claiming fuel, insurance, repairs and capital allowances for that vehicle.
- Working from home 25+ hours a month: £10 per month (25 to 50 hours), £18 (51 to 100), £26 (101+). Phone and internet are claimed separately on actual business use.
The trading allowance
If your gross trading income is £1,000 or less in a tax year, it is covered by the trading allowance and you may not need to report it at all. Above that, you can choose to deduct the flat £1,000 allowance instead of your actual expenses, which suits businesses with very low costs. You cannot use the allowance to create a loss, and it is measured against gross income before any expenses.
How QuickMaths uses these categories
The bank statement analyzer and receipt scanner assign each transaction to a category aligned with these boxes (cost of goods, staff costs, vehicle and travel, rent/rates/insurance, repairs, office costs, advertising, professional fees, bank charges, other), flag personal and transfer items so they stay out of your business totals, and export the result to Excel with per-category sheets. The output maps onto the SA103F boxes and onto MTD quarterly update categories.