Average order value is revenue divided by the number of orders. Net AOV, net revenue over net orders, is the version to compare against per-order costs, because shipping, packing and the fixed part of a payment fee are charged per order rather than per euro of revenue.
It matters because a falling AOV raises the share of every order those per-order costs eat, even when nothing about the costs changed. Twenty-five cents of fixed payment fee is 1,25% of a €20 basket and noise on a €500 one; the same is true of every parcel.
Gross AOV uses gross revenue and gross orders and is fine for spotting trends; net AOV is the one that belongs next to your cost per order, and the two drift apart exactly when discounts or returns move.
If you are pushing bundles or free-shipping thresholds, this is the number that tells you whether it worked, and the Shopify payment fees calculator shows what a shifting basket does to your blended fee rate.
