Most successful UK online sellers do not stick to one platform. You might sell vintage on Depop, electronics on eBay, handmade on Etsy, and run live auctions on Whatnot. By tax time, you are staring at five different dashboards, three different payment processors, and a vague hope that the numbers will somehow add up.
Here is how to actually track multi-platform sales properly so your tax return takes hours, not weeks.
Why HMRC sees one business, not five
A common misconception is that each platform is a separate business. It is not. HMRC treats your trading activity as a single self-employment, regardless of how many platforms or shops you operate. You file one self-assessment, declare one total income figure, and claim one set of expenses.
This is actually good news. It means losses on one platform offset profits on another. It also means you get one £1,000 trading allowance, not £1,000 per platform.
The two ways to track multi-platform sales
Option 1: Spreadsheet method
For sellers turning over less than £30k a year, a well-built spreadsheet is often enough. Set up columns for: date, platform, item description, gross sale price, platform fees, payment processor fees, postage cost, and net proceeds. Update it weekly. At year-end, you have a clean total.
The downside: it relies on you doing the data entry. Miss a few weeks and reconstructing it from memory is brutal.
Option 2: Accounting software
For anything more serious, use bookkeeping software like Xero or QuickBooks. Both can connect directly to your bank feed and many can pull data from PayPal, Stripe, and Wise. Some accountants (including Simplr) can also integrate platform-specific connectors that pull Etsy or eBay sales automatically.
From April 2026 onwards, sole traders earning over £50k will be required to use Making Tax Digital compatible software anyway. If your business is growing, get on this now rather than later.
What you must capture for each sale
For tax purposes, you need to be able to evidence:
- Gross sale price (what the buyer paid)
- Platform fees (Etsy listing fee, Vinted seller protection, etc.)
- Payment processor fees (PayPal, Stripe, Wise)
- Postage and packaging costs
- Any returns or refunds
- VAT (if registered) — both charged and reclaimed
Reconciling payouts to your bank
One of the trickiest parts of multi-platform selling is that what hits your bank account is rarely what you actually earned. eBay batches payouts. Vinted holds funds until items arrive. Etsy releases payouts on a schedule. PayPal sometimes holds funds for risk review.
Reconcile each platform separately. The income on your tax return should be your gross sales (before fees), with fees claimed as expenses. Do not just declare what landed in your bank account — that understates your turnover and overstates your profit margin.
Currency conversions for international sales
If you sell to overseas buyers, your platform may pay you in foreign currency. HMRC requires sales to be reported in GBP using the rate at the date of the transaction. Most accounting software handles this automatically. If you are doing it manually, use the HMRC monthly average exchange rate or the spot rate from the Bank of England.
Common multi-platform tax mistakes
- Only declaring one platform: HMRC will spot this from the marketplace reporting data
- Declaring net (after fees) instead of gross sales
- Forgetting to claim postage and packaging as expenses
- Missing PayPal or Stripe fees as deductions
- Not tracking returns and refunds (these reduce taxable income)
- Mixing personal and business transactions in the same bank account
When to bring in an accountant
If you are turning over £30k+ across multiple platforms, the time saved by hiring a specialist accountant pays for itself many times over. We see plenty of sellers who were paying too much tax simply because they were not capturing all their deductible expenses, or paying too little and risking an HMRC enquiry. See how we work with Amazon FBA sellers for an example of how specialist accounting changes the picture.
At Simplr Accounting, we set up multi-platform sellers with proper bookkeeping systems, integrate with platforms where possible, and handle your self-assessment so it is done right. Book a free discovery call to see how we can simplify your tax life.