Self Assessment for resellers UK: register, file and pay
If you buy stock to sell at a profit and your gross trading income passes £1,000 in a tax year, you need to register for Self Assessment and file a tax return. This guide covers the order you do it in, and the dates that cost money when you miss them.
TLDR: Register by 5 October after the tax year in which you passed £1,000. File online and pay by 31 January. Keep a record of every purchase, sale, fee and postage cost from day one.
This is general information from gov.uk, not personal tax advice. If you are not sure whether you are trading at all, read do you pay tax on reselling in the UK first. That post covers the badges of trade and the £1,000 trading allowance in detail.
Step 1: confirm the tax year
The UK tax year runs from 6 April to 5 April. Everything on your return uses those dates.
Platform reports do not. eBay, Vinted and other marketplaces report to HMRC by calendar year, so the figure in a platform's annual summary will not match your tax year. Build your own totals from your sales exports.
Step 2: register as self-employed
Register on gov.uk as a sole trader. You need your National Insurance number and basic details about the business, such as what you sell and when you started.
The deadline is 5 October after the end of the tax year in which you started trading above the allowance. If you passed £1,000 in the 2026 to 2027 tax year, which ends on 5 April 2027, register by 5 October 2027.
HMRC then sends you a Unique Taxpayer Reference (UTR), a 10-digit number. You need it to file. Register early, because the return cannot go in without it.
Step 3: choose the trading allowance or real expenses
You have two choices for reducing the income HMRC taxes. You cannot use both.
- The £1,000 trading allowance. Take £1,000 off your gross income and claim no expenses.
- Real expenses. Take off what the business actually cost you: stock, platform and payment fees, postage and packaging, and other allowable costs.
For most resellers, real expenses win by a long way, because stock is the biggest cost. If you turned over £6,000 and the stock cost £4,500, the allowance saves you tax on £1,000. Real expenses save you tax on £4,500 plus fees and postage.
Step 4: work out the numbers
Since the 2024 to 2025 tax year, the cash basis is the default for sole traders. In plain terms, you count money when it comes in and goes out.
Your return needs two main figures:
- Turnover. The total of your sales, including the postage your buyers paid you.
- Allowable expenses. Stock bought for resale, selling fees, payment fees, postage, packaging, and similar costs.
Profit is turnover minus expenses. Tax is then worked out on your total income for the year, which includes any wages from a job.
A simple spreadsheet is enough: date, item, cost, sale price, fees and postage. Our reselling profit tracker guide shows what to record for each sale.
Step 5: file the return online
Sign in to your HMRC online account and complete the Self Assessment return. The online service asks questions in order and works the tax out for you.
There is a short self-employment section for businesses with turnover below the VAT threshold, which covers most resellers. You enter turnover and total expenses, not each sale.
The deadlines for each tax year are:
| What | Deadline |
|---|---|
| Register for Self Assessment | 5 October after the tax year ends |
| Paper return | 31 October after the tax year ends |
| Online return | 31 January after the tax year ends |
| Pay the tax you owe | 31 January after the tax year ends |
Step 6: pay, and plan for payments on account
Pay the bill by 31 January. If you file late, HMRC charges a £100 penalty, even if you owe no tax. Late payment adds interest and can add further penalties.
Payments on account catch many first-year resellers out. If your Self Assessment bill is more than £1,000, HMRC usually asks for two advance payments towards next year's bill, each half of this year's bill. They are due on 31 January and 31 July. The exception is when most of your tax is already collected at source, for example through PAYE.
So a first bill can be much bigger than expected: this year's tax, plus half of it again in advance. Put money aside from each sale, not in January.
What National Insurance applies?
Self-employed people pay Class 4 National Insurance on profits above £12,570. The main rate is 6%. Class 2 contributions are no longer compulsory, so most resellers do not pay them.
Making Tax Digital is coming for bigger sellers
Making Tax Digital for Income Tax started in April 2026 for sole traders with qualifying income over £50,000. From April 2027 the threshold falls to £30,000. Qualifying income is your gross self-employment and property income, not your profit.
If you are in scope, you keep digital records and send quarterly updates using compatible software. Check the gov.uk rules if your turnover is near those figures.
Where this connects
Tax is calculated on profit, and profit is decided when you buy. Buying at RRP rather than from a scalper is what keeps a margin left over after fees, postage and tax. Paragn runs monitors across more than 1,000 UK retailers so members can buy at retail price. See how Paragn Network membership works, or read sole trader or limited company if your profits are growing.
Common questions
When do I need to register for Self Assessment as a reseller?
Register by 5 October after the end of the tax year in which your gross trading income went over £1,000. The tax year ends on 5 April.
Can I claim the cost of my stock?
Yes, if you claim real expenses. Stock bought for resale is an allowable expense, as are selling fees, payment fees, postage and packaging. You cannot claim them if you use the £1,000 trading allowance instead.
What happens if I file my tax return late?
HMRC charges a £100 penalty as soon as an online return is late, even if you owe no tax. The penalties increase the longer the return is late, and late payment adds interest.
What are payments on account?
They are two advance payments towards next year's tax bill, due on 31 January and 31 July. HMRC usually asks for them when your Self Assessment bill is more than £1,000.
Do I need an accountant to file as a reseller?
No. Most small resellers file online themselves. An accountant is worth considering when your turnover grows, when you are near the Making Tax Digital thresholds, or when you are not sure whether you are trading.