Hamster blog

How to fill in the SA103S self-employment pages for a side hustle

By the Hamster team · Published 25 October 2026

Last checked: 25 October 2026 against GOV.UK · Figures are for the 2026–27 tax year unless stated

Short pages or full pages?

The SA103S "Self-employment (short)" pages are for most side hustles. The 2025–26 notes say to use them if your turnover was less than £90,000, or would have been over a full year. You need the full SA103F pages instead if, for example, your business is more complicated, your accounts were made up to a date before 31 March 2026, or you changed accounting basis.

If you have two separate businesses, each one gets its own self-employment pages.

This guide is for the return due on 31 January 2027, which covers 6 April 2025 to 5 April 2026. If you file online, you enter the same figures. The box numbers below come from the paper form and its notes.

Business details: boxes 1 to 8

• Box 1: a short description, such as "reselling clothes online" or "private tutoring".
• Box 2: the postcode of your business address. For most side hustles that is home.
• Box 3: put an X if your business name, description, address or postcode changed in the last 12 months.
• Box 4: only for foster carers and shared lives carers.
• Boxes 5Q and 5: did the business start after 5 April 2025? If yes, put the start date in box 5.
• Boxes 6Q and 6: did it stop before 6 April 2026? If yes, put your final trading date in box 6.
• Box 7: the date your books are made up to. Most side hustles use the tax year, so 05 04 2026.
• Box 8: put an X only if you used traditional accounting. Leave it blank if you used cash basis, which records money when it actually comes in and goes out.

Income: boxes 9 to 10.1

Box 9, turnover, is everything your business took before expenses. The notes say to include cash, card and other payments, tips, fees and commissions, and payments in kind, such as products you were given for promoting them.

Box 10 is other business income that is not part of your turnover. Most side hustles leave it blank.

Box 10.1 is the £1,000 trading allowance. If you claim it here, you cannot claim any expenses or capital allowances. You cannot use it to make a loss, and if you have more than one self-employment, the total you claim across them cannot be more than £1,000.

Expenses: boxes 11 to 20

If you claimed the trading allowance in box 10.1, leave boxes 11 to 20 blank.

Otherwise, either split your allowable expenses across boxes 11 to 19, or, with turnover under £90,000, put the total straight into box 20. The full-page notes describe what belongs in each category:

• Box 11, goods bought for resale or goods used: stock, raw materials and the direct costs of producing what you sell.
• Box 12, car, van and travel: fuel, insurance, repairs, parking, train and taxi fares, or your flat-rate mileage, after taking off private use.
• Box 13, wages and staff costs: if you pay anyone to help. Never payments to yourself.
• Box 14, rent, rates, power and insurance: including the business share of running your home, or the flat rate for working from home.
• Box 15, repairs and maintenance of business premises and equipment.
• Box 16, accountancy, legal and other professional fees.
• Box 17, interest and bank and credit card charges on business borrowing and accounts.
• Box 18, phone, stationery and other office costs: phone bills, postage, stationery, printing and software.
• Box 19, other allowable expenses: for example advertising and subscriptions. The form reminds you that client entertaining is not allowable.
• Box 20: the total of boxes 11 to 19.

Profit: boxes 21 to 32

• Box 21, net profit: box 9 plus box 10, minus box 20. Box 22 is the net loss if expenses were larger.
• Boxes 23 to 26, capital allowances: for equipment and vehicles if you used traditional accounting. On cash basis you only claim capital allowances for buying a car. Leave these blank if you claimed the trading allowance.
• Box 27, goods for your own use: stock you took out of the business for yourself, usually at cost.
• Box 28, net business profit for tax purposes: box 21 plus boxes 26 and 27, minus your capital allowances, or minus box 10.1 if you claimed the trading allowance.
• Box 29: losses from earlier years that you are using against this year's profit.
• Box 30: other business income not included in boxes 9 or 10.
• Box 31, total taxable profits: box 28 plus box 30, minus box 29. This is the figure your Income Tax and National Insurance are worked out on.
• Box 32: your net business loss, if there is one.

Losses, National Insurance and CIS: boxes 33 to 38

• Boxes 33 to 35: how you want to use a loss. You cannot fill in box 33 if you claimed the trading allowance.
• Box 36: put an X to pay voluntary Class 2 National Insurance if your total profits for 2025–26 were under £6,845. You cannot pay voluntarily through Self Assessment after 31 January 2027. See National Insurance on side hustle income.
• Box 37: only if you are exempt from Class 4, for example because you reached State Pension age on or before 6 April 2025.
• Box 38: Construction Industry Scheme deductions, for CIS subcontractors only.

Worked example 1: claiming expenses

Grace has a job and resells vintage clothes. In 2025–26 she took £9,800, spent £4,100 on stock, £620 on postage, packaging and labels, and £300 on promoted listings.

• Box 9: £9,800
• Box 11: £4,100 (stock)
• Box 18: £620 (postage and packaging)
• Box 19: £300 (advertising)
• Box 20: £5,020
• Box 21: £9,800 − £5,020 = £4,780
• Box 28: £4,780
• Box 31: £4,780

Her salary uses her Personal Allowance, so her side hustle profit is taxed at 20%: £956. It is under £12,570, so there is no Class 4 National Insurance.

Worked example 2: claiming the trading allowance

Jess babysits at weekends alongside a job. In 2025–26 she was paid £2,400 and spent almost nothing.

• Box 9: £2,400
• Box 10.1: £1,000
• Boxes 11 to 20: blank
• Box 21: £2,400
• Box 28: £2,400 − £1,000 = £1,400
• Box 31: £1,400

Taxed at 20%, that is £280.

Common mistakes

• Putting profit in box 9. Box 9 is turnover, before any costs.
• Claiming the allowance and expenses. It is one or the other.
• Using this year's mileage rate. For 2025–26 the car rate was 45p a mile for the first 10,000 business miles. The 55p rate only applies from 6 April 2026.
• Leaving out payments in kind, such as gifted products for creators.
• Claiming the private share of a car, phone or home.

Keeping track

Most of the work on these pages is having the right totals. Hamster is a free Android app that adds up your turnover and costs through the tax year as you log them, and with Premium it exports a PDF with the figures labelled by SA103S box, ready to copy into your return.

This is general information, not personal tax advice. Rules and rates change — check the linked GOV.UK pages or speak to an accountant about your own situation.