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Merge Amazon Seller Central and BigCommerce Sales Data for Tax Prep in the United Kingdom

At tax time you need total revenue by channel without hand-fixing each export's columns first. In the United Kingdom, that also means accounting for VAT: VAT is charged at a flat 20% standard rate once you're registered, and HMRC expects consistent digital records under Making Tax Digital.

Why Amazon Seller Central and BigCommerce exports don't line up

Amazon Seller Central: a purchase date/time column stamped in UTC, not your local time; item price, promotion discounts, and Amazon referral fees split across several columns; an Amazon Order ID in a long dashed format (e.g. 123-4567890-1234567).
BigCommerce: an Order Date column that includes a full timestamp; Subtotal and Grand Total both included, which are easy to mix up when mapping; a numeric Order ID.

Neither export is built with VAT in mind, so getting from "two raw files" to "the United Kingdom-ready numbers" means normalizing dates/totals first, then applying your own VAT treatment on top of the merged total — not per platform separately.

How to merge them

Set your target columns once in CSV Experts (Date, Channel, Order ID, Total, and a Currency column if you sell in more than GBP).
Map the Amazon Seller Central export, then the BigCommerce export — each file shape is remembered after the first time.
Export the merged sheet and apply your VAT treatment to the combined total.

Merge your files now →

FAQ

Does this upload my sales data anywhere?

No. Everything runs in your browser using JavaScript — your files are never sent to a server.

Does it work for more than two channels?

Yes. Add as many source files as you want; each distinct file layout is mapped once and remembered.

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