SA103S vs SA103F: which Self-Assessment form do you need?

Quick breakdown:
SA103S (Short form):
- Turnover under £90,000
- No employees
- No capital allowances over £1,000
- Simple expenses
Most first-year sole traders use this.

SA103F (Full form):
- Turnover £90k+
- VAT registered
- Employees on payroll
- Capital allowances (expensive equipment)
- CIS deductions

If you're earning under £90k and your expenses are straightforward (mileage, software, marketing, office costs), you want SA103S.

It's 4 pages vs 8 pages. Box numbers are the same, just fewer boxes to fill.

Pro tip: SA103S only has 14 expense boxes (11-24). Learn which box each of your regular expenses goes in, and filing becomes 10x easier.

Example:
- Box 12: Mileage, car costs, travel
- Box 16: Software, phone, office supplies
- Box 17: Advertising, marketing
- Box 20: Professional fees, training
Knowing these upfront saves you hours of googling in January.

This is a general guidance. If you have a complex situation or unsure which form? Please speak to a qualified accountant.