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Merge Squarespace and BigCommerce Sales Data for Tax Prep

At tax time you need total revenue by channel without hand-fixing each export's columns first.

Why Squarespace and BigCommerce exports don't line up

Squarespace: a Date column in ISO-like format; Subtotal, Discount, Shipping, and Total as separate columns; an Order ID that's a short alphanumeric code. Also, customer and shipping address fields are wide, so the money and date columns can end up far to the right of the sheet.
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. Also, many optional columns are exported blank depending on store configuration, which can throw off auto-mapping by header position.

For tax prep, that mismatch is exactly what causes hours of manual cleanup every period.

Open CSV Experts and set your target columns once (Date, Channel, Order ID, Total).
Drop in your Squarespace export and map its columns once.
Drop in your BigCommerce export and map it the same way — both merge into one sheet, normalized.
Export as CSV or Excel. Same-layout files merge automatically next time.

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

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