COGS or Cost of Goods Sold is calculated as follows:
COGS = number of units sold * landing cost price
If landing cost price is not set the cost price field is used.
Landing cost price is the total unit cost for including cost price and related expenses. In addition to vendor cost it includes shipping & handling, and discounts. Landing cost is the cost price in addition to extra expenses (and not only the extra expenses).
Note: For EU merchants, VAT should be included as part of the Cost Price. VAT is EU-specific. In the landing cost price calculation Inventory Planner only considers shipping/handling and discounts. Tax is not counted - so to accommodate this it should be represented in the Cost Price to make sure it's factored in with the landing cost price calculation.
If you do not see data showing for COGS, this will update when you import or enter your landing cost or cost prices. By default, the current landing cost (or if landing cost is not set, then cost price) is used to calculate COGS. This calculation is not using the historical landing cost price.