How to fill in your tax return as a reseller

Before you start

• Your UTR, the 10-digit number HMRC posted when you registered.
• Your sales for the tax year, 6 April to 5 April: everything buyers paid you, before any costs.
• Your expenses for the same year: stock, fees, postage and the rest. The expenses guide covers what counts.
• Any other income, like wages from a job, which goes elsewhere on the return.

Short pages or full pages?

The self-employment section comes in a short and a full version. Use the short one if your turnover was under £90,000 and your business is simple. Buying and reselling things almost always is. Use the full version if turnover was £90,000 or more or things are more complicated.

The boxes that matter

These are the box numbers on HMRC's short self-employment pages for the 2025 to 2026 return. Online the boxes appear as questions, but the figures are the same.

• Box 1, description of business: something plain like "Online resale of second-hand goods".
• Box 9, your turnover: the total you received from sales before taking off any expenses.
• Box 10.1, trading income allowance: only if you're taking the £1,000 allowance instead of claiming expenses. If you fill this in, leave the expenses boxes empty.
• Box 20, total allowable expenses: with turnover under £90,000 you can put your expenses in here as one total rather than splitting them across boxes 11 to 19.
• Box 21, net profit: turnover (plus any other business income in box 10) minus the expenses.

Box 8 is only for people using traditional accounting. The cash basis, where you record money when it actually comes in and goes out, is now the standard way, so most resellers leave box 8 empty.

After you submit

Your Income Tax and Class 4 National Insurance are worked out from the profit. Both are due by 31 January, the same day as the return. Paper returns have an earlier deadline, 31 October.

Payments on account: the one that catches people out

If your bill is £1,000 or more, and less than 80% of your tax was already taken at source (through a job's PAYE, for example), HMRC asks for advance payments towards next year's bill. Each one is half of this year's, due on 31 January and 31 July.

In your first year that means paying this year's bill plus half of it again in January, then the other half in July. A £2,000 bill becomes £3,000 in January and £1,000 in July. The advance payments come off the following year's bill, so nothing is paid twice, but the first January is a shock if you don't expect it.

Keep everything

Keep your records for at least 5 years after the 31 January deadline for the year. If HMRC ever asks how you got to a figure, the records are your answer.

Where STC fits in

STC's Tax screen gives you the figures in the order the return asks for them. Set the dates to 6 April to 5 April and it shows the revenue for box 9, the costs, fees, postage and expenses that make up box 20, and the profit for box 21. Export CSV keeps a copy with your records.