Self Assessment for online sellers: a simple walkthrough

If your reselling has grown past the £1,000 trading allowance, you will usually need to do a Self Assessment tax return. It sounds more daunting than it is. Here is the whole thing in plain English, from registering to filing, with the dates that matter.

General information, not tax advice. Check with HMRC or a qualified accountant before you act on it.

Do you actually need to do one?

You normally need to register for Self Assessment if your total trading sales in a tax year go over £1,000. That is sales before costs, not profit. If you are under £1,000, or you are only selling your own used belongings, you usually do not need to do a return at all. If you are over, read on.

Step 1: register (deadline 5 October)

The first step is telling HMRC you need to file. You register for Self Assessment as self-employed on the gov.uk website. The deadline is 5 October in the tax year after you went over the allowance. So if you crossed £1,000 in the 2026/27 tax year, you register by 5 October 2027. When you register, HMRC sends you a Unique Taxpayer Reference, which you will need to file, so do not leave this to the last minute.

Step 2: keep simple records

You do not need fancy accounting software. Through the year, keep a note of your total sales, your selling fees, your postage and packaging costs, and what you paid for any stock you resold. A spreadsheet is fine. These are the numbers you will put on your return, and good records mean you claim every cost you are allowed and pay no more tax than you need to.

Step 3: work out your taxable profit

Your taxable profit is your sales minus your allowable costs. You can choose to deduct either the flat £1,000 trading allowance or your real costs, whichever is higher. On top of that, everyone has a £12,570 personal allowance for 2026/27. If your reselling profit plus any other income such as a day job stays under that, there is often no income tax, although Class 4 National Insurance can apply once profits pass its threshold.

Step 4: file and pay (deadline 31 January)

You file your online return and pay any tax due by 31 January after the end of the tax year. For the 2026/27 tax year, that is 31 January 2028. The return itself is mostly entering the figures you already gathered. If you owe nothing after your allowances, you still file, but there is nothing to pay.

The £100 penalty to avoid

Miss the 31 January filing deadline and HMRC charges an automatic £100 penalty, even if you owe no tax. Leave it longer and further penalties and interest can build up. This is the one date really worth putting in your calendar. Filing early, even in the autumn, is completely allowed and takes the pressure off.

What you need, in one list

• Your Unique Taxpayer Reference and a Government Gateway login.
• Your total sales for the tax year.
• Your costs: fees, postage, packaging and the cost of stock.
• Details of any other income, like a job salary, so tax is worked out correctly.

Making it easier

The fiddly part is gathering accurate figures from your sales. FlipTally pulls your eBay and Vinted numbers together, works out your profit and lines the figures up against the Self Assessment boxes, which saves the shoebox-of-receipts panic in January. However you do it, remember this is general information rather than advice, so check anything important with HMRC or an accountant.

Frequently asked questions

This guide is general information, not tax advice, and reflects the UK rules for the current tax year. Always check with a qualified accountant before you file. FlipTally is independent and not affiliated with, endorsed by or connected to eBay, Vinted, Depop or HMRC. Last updated 2026-08-03.