In Shopify, cost is maintained at the variant level, and in Better Reports, COGS (calculated as variant cost × quantity sold) always uses the latest cost value from Shopify.
This differs from Shopify’s built-in COGS reporting, which does not update if a cost is entered after a sale. Since Shopify does not store historical cost data, it isn’t possible to measure the exact cost of a product at the time it was sold.
In Better Reports, as a conservative approach, any variant without a cost is treated as having 100% cost of goods sold and 0% gross margin (COGS = Net Sales).
To resolve this, you can setup your variant costs in Shopify. This link is also available at the top of the built-in All-time sales report, or any other report that includes COGS data.
You can refer to the built-in Variants without cost report, which lists all variants without a recorded cost. Once you update the costs in Shopify, this report will automatically refresh.
If you have a preferred calculation of COGS for variants without cost recorded, feel free to reach out to us at hello@betterreports.com! We'd be happy to help you create custom COGS fields with your preferred calculation.