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The Best Way to Merge Amazon Seller Central and BigCommerce Data for Quarterly Tax Estimates

If you're doing quarterly tax estimates by hand right now, here's the fastest path from "two exports" to "one usable sheet," and why the manual version keeps breaking.

Step by step

  1. Decide your target columns once. Most people settle on Date, Channel, Order ID, and Total — set that up in CSV Experts and you won't redo it.
  2. Import the Amazon Seller Central file first. The first time you see this file shape, you map each of its columns to your target list.
  3. Import the BigCommerce file the same way. Its columns get mapped once too — after that, every future file with this shape merges with no extra clicks.
  4. Check the merged totals. Dates and numbers are normalized automatically, so a European "24,00" and a US "24.00" both land as the same value.
  5. Export. CSV or Excel, ready for quarterly tax estimates.

What actually goes wrong if you do this by hand

Amazon Seller Central gives you a purchase date/time column stamped in UTC, not your local time, while BigCommerce gives you an Order Date column that includes a full timestamp — line those up manually across a few hundred rows and it's easy to miscount a week. On top of that, Amazon Seller Central's export reports differ noticeably between the 'All Orders' report and the Payments/Settlement report — totals rarely match at a glance, and BigCommerce's many optional columns are exported blank depending on store configuration, which can throw off auto-mapping by header position. Individually those are minor quirks; combined into one spreadsheet by hand, they're where most reconciliation errors for quarterly tax estimates actually come from.

Why it matters for quarterly tax estimates

Quarterly estimated tax payments depend on knowing real revenue across every channel, not just the platform that's easiest to check.

Try it with your own files →

Just want the quick column-difference reference instead? See the short version.

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