Question 1

What's the difference between the SA103S and SA103F?

Accepted Answer

The SA103S is the short version for simpler businesses with turnover under the VAT threshold (£85,000 for 2025/26). The SA103F is the full version required when turnover exceeds the threshold, when you need to claim capital allowances separately, or when your business is more complex. Both accompany your main SA100 Self Assessment return. TradeTally works for both — the export follows the SA103F box layout either way.

Question 2

Can TradeTally auto-fill my SA103F?

Accepted Answer

TradeTally tracks your income and expenses throughout the year and maps every category to its SA103F box. At tax time, the Export → Tax Return action produces a pre-filled SA103F summary showing exactly which figure goes in each box. You can then enter those figures in HMRC's online filing system or hand the export to your accountant. TradeTally does not submit returns directly to HMRC.

Question 3

When is the SA103F deadline for the 2025/26 tax year?

Accepted Answer

The online filing deadline is 31 January 2027. Paper returns must reach HMRC by 31 October 2026. Late filing incurs an automatic £100 penalty, with further penalties for continued delay. (Source: GOV.UK.)

Question 4

Do I need an accountant to fill in the SA103F?

Accepted Answer

You are not legally required to use an accountant. Many sole traders successfully file their own SA103F using software like TradeTally to track their figures throughout the year. If your affairs are complex, you have significant capital allowances to claim, or you are unsure about any aspect of the form, professional advice can be worthwhile — and accountancy fees are themselves a deductible expense.

Question 5

What if my expenses don't fit the standard categories?

Accepted Answer

TradeTally has 12 built-in expense categories mapped to SA103F boxes. Costs that don't fit can be logged under OTHER with a description — the year-end summary surfaces them as other expenses and your accountant can advise on the right box at filing time.

Question 6

Does TradeTally handle CIS deductions in the SA103F?

Accepted Answer

Yes. Subcontractor expenses log into SA103F box 18 (Payments to subcontractors). For sole traders who also work as subcontractors, CIS deductions taken from your invoices by main contractors can be recorded against each payment, and they appear in the year-end summary in the right place. The CIS guide has more detail.

TradeTally category	SA103F box
Income (paid invoices)	Box 15 (and 16 for goods/services split)
Materials	Box 17 (Cost of goods bought for resale or use)
Subcontractor payments (CIS)	Box 18 (Payments to subcontractors)
Wages, salaries, pensions	Box 19 (Wages and salaries)
Vehicle / fuel / mileage	Box 20 (Travel and subsistence)
Rent, rates, power, insurance	Boxes 22-23 (Premises and administrative costs)
Repairs, advertising, legal, software	Boxes 24-29 (Other allowable expenses)
Total expenses, profit	Box 31 (Net profit or loss)

SA103F software for UK sole traders

How TradeTally maps to the SA103F boxes

What "SA103F-ready" actually means

Related guides and tools

Keep your SA103F boxes filled in throughout the year