Sole trader accounting for online sellers and marketplace businesses

Selling online can feel simple at the start. You list a few products, receive payments through Amazon, Etsy, eBay, Shopify, Vinted, TikTok Shop or your own website, and the money starts coming in. But once orders, fees, postage, returns and stock purchases build up, your accounting can become messy very quickly.

As a sole trader, you are personally responsible for keeping accurate records, reporting your profit correctly and paying the right amount of tax to HMRC. That does not mean you need to overcomplicate things. It simply means you need a clear system that keeps your sales, costs and tax position easy to understand.

Online retail remains a major part of the UK economy, with online sales making up around 28.1% of retail sales in April 2026. For online sellers, that means opportunity, but also more competition, tighter margins and more need for proper bookkeeping.

Why online sellers need clean accounting from the start

Marketplace businesses are different from many traditional sole trader businesses. You may receive hundreds of small payments rather than a few large invoices. You may also pay platform fees, payment processing fees, listing fees, advertising costs, postage, packaging, refunds and stock costs.

If you only look at the amount landing in your bank account, you may not see the full picture. For example, a product sold for £40 might look profitable, but once you deduct marketplace commission, postage, packaging, card fees and the original stock cost, the real profit may be much smaller.

This is where working with an accountant for sole trader businesses can help. You get a clearer view of what you are actually earning, not just what your marketplace dashboard shows.

Know the difference between sales and profit

One of the most common mistakes online sellers make is confusing turnover with profit.

Your turnover is your total sales income before costs. Your profit is what is left after allowable business expenses. HMRC taxes your profit, not your total sales, but your turnover still matters for VAT, Making Tax Digital and business planning.

For example, if you sell £60,000 worth of products in a year and your costs are £38,000, your taxable profit is not £60,000. It is closer to £22,000 before any other adjustments. However, that £60,000 turnover may still affect whether you need to think about VAT or digital tax reporting.

A self-employed accountant can help you separate sales, fees, stock costs and expenses properly so you do not overpay tax or understate your income.

Keep marketplace records, not just bank records

Your bank statement is useful, but it does not tell the full story. Marketplaces often deduct fees before paying you. This means the amount received into your bank may be lower than your actual sales.

For example, you might sell £1,000 of products in a week, but receive £870 after marketplace fees, advertising charges and refunds. For accounting purposes, you still need to understand the full £1,000 sales figure and the £130 of deductions.

You should keep records of:

• Marketplace sales reports
• Platform fees and commission
• Refunds and returns
• Advertising spend
• Postage and fulfilment costs
• Stock purchases
• Packaging costs
• Payment processor fees
• Business mileage, where relevant
• Software subscriptions

Good sole trader accountancy services will help you record these correctly, rather than relying only on what appears in your bank account.

Understand HMRC’s online platform reporting rules

Since January 2024, many digital platforms have been required to collect and report seller information to HMRC. This does not automatically mean you owe tax, but it does mean HMRC may receive more information about online selling activity.

If you are simply selling unwanted personal items from your home, you may not need to pay tax. But if you buy or make goods with the intention of selling them for profit, HMRC is likely to treat this as trading.

The £1,000 trading allowance is also important. If your total trading income is more than £1,000 in a tax year, you may need to tell HMRC about it, even if your profit is small.

This is why clear sole trader accounting support is useful. You do not want to guess whether your activity is casual selling or a taxable business.

Watch the VAT threshold carefully

VAT is one of the biggest areas online sellers need to monitor. In the UK, you must register for VAT if your taxable turnover goes over £90,000 in any rolling 12-month period, or if you expect it to go over £90,000 in the next 30 days.

This is not based on your accounting year. It is a rolling 12-month test, which means you should keep checking it throughout the year.

For online sellers, VAT can affect your pricing and margins. If you sell mainly to consumers, adding VAT may make your products look more expensive unless you adjust your pricing carefully. If you sell to VAT-registered businesses, VAT may be less of a problem because they may be able to reclaim it.

A VAT return accountant can help you decide when to register, how to price your products, which VAT scheme may suit you and how to file VAT returns correctly.

Use software that matches how you sell

Spreadsheets can work at the start, but they often become difficult once you have regular orders, multiple platforms and stock to track. Accounting software can help you connect bank feeds, categorise expenses and prepare better records.

If you sell through platforms such as Shopify, Amazon, eBay or Etsy, it is worth setting things up properly so sales, fees and payouts are recorded in the right way. A certified QuickBooks accountant can help you avoid messy imports and duplicated income.

This matters even more as Making Tax Digital for Income Tax is now being phased in. From 6 April 2026, sole traders and landlords with qualifying income over £50,000 must use compatible software to keep digital records and send quarterly updates to HMRC. The threshold is due to reduce in later phases, so getting ready early is sensible.

Do not forget stock and cost of goods sold

If you sell products, your stock records matter. You need to know what you bought, what you sold, what remains unsold and what has been returned, damaged or written off.

Your profit is not simply sales minus bank payments. You need to account for the cost of the stock you actually sold. If you buy £10,000 of stock in March but only sell half of it before your year-end, the full £10,000 may not all be treated as a cost for that year.

This is where many online sellers get confused. Keeping simple stock records helps you understand your true margins and prevents your accounts from becoming inaccurate.

Claim the right expenses

As an online seller, you may be able to claim many business-related costs, including marketplace fees, postage, packaging, stock, website costs, software, advertising, accountancy fees, business banking fees and some home office costs.

The key is that expenses must be wholly and exclusively for business purposes. If something is partly personal and partly business, you need to claim only the business element.

Working with accountants for self-employed individuals can help you claim what you are entitled to without pushing into risky territory.

Plan for your tax bill throughout the year

Because tax is not deducted automatically from most sole trader income, it is easy to spend money that should have been set aside for HMRC.

A simple approach is to move a percentage of your profit into a separate tax savings account every month. The exact percentage depends on your income level, National Insurance, other earnings and whether you make payments on account.

If you work with a self-assessment tax return accountant, you can get a clearer estimate before the 31 January deadline, instead of finding out too late.

When should you get professional help?

You may be able to handle your own records when sales are low and simple. But once you are selling regularly, using multiple platforms, approaching the VAT threshold or struggling to understand your profit, it is worth getting support.

As chartered accountants in Slough, Asmat & Co Accountants helps sole traders and small businesses keep their accounts clear, compliant and easier to manage.

Professional sole trader accounting services can help you with bookkeeping, tax returns, VAT, QuickBooks setup, HMRC deadlines and year-round advice, so you can spend less time worrying about numbers and more time growing your online business.

Final thoughts

Online selling can be a great way to build a flexible business, but the accounting needs proper attention. Marketplace payouts, fees, VAT, stock and digital reporting can all affect your tax position.

The earlier you put a simple system in place, the easier everything becomes. You will know which products are profitable, how much tax to set aside and whether your business is ready to grow.

If you sell through online marketplaces and want clear, practical accounting support, contact Asmat & Co Accountants today. We can help you organise your records, stay compliant with HMRC and build a better picture of your online business finances.

FAQs

Do I need to register as self-employed if I sell online?

You may need to register as self-employed if you buy or make goods with the intention of selling them for profit and your total trading income is more than £1,000 in a tax year. Selling unwanted personal items from home is usually different, but regular profit-making activity should be checked carefully.

Do marketplace platforms report my sales to HMRC?

Yes, many digital platforms now collect and report seller information to HMRC. This does not automatically mean you owe tax, but it does mean your online selling activity may be visible to HMRC, so your records should be accurate.

Do I pay tax on total sales or profit?

As a sole trader, you usually pay tax on profit, not total sales. Profit is your income after allowable business expenses. However, turnover is still important for VAT, Making Tax Digital and deciding whether you need to report income to HMRC.

When do online sellers need to register for VAT?

You must register for VAT if your taxable turnover goes over £90,000 in a rolling 12-month period, or if you expect it to go over £90,000 in the next 30 days. Some sellers also choose to register voluntarily, depending on their costs and customers.

Can I claim marketplace fees and postage as expenses?

Yes, if they are business costs linked to your online selling activity. Marketplace commission, listing fees, payment processing charges, postage, packaging and advertising costs are common examples of expenses that may be allowable.