Blank is missing, not zero; enter 0 where a cost does not apply. Only net shipping cost may be negative. Nothing you enter is stored or sent anywhere.
Reminders. Do not deduct refunds twice. Do not subtract an overhead allocation per order and then subtract the same full overhead again in a monthly total. Keep the revenue scope aligned with the spending scope, and compare estimates with actual orders and a higher-cost scenario.
For the reasoning behind each line, read The Ecommerce Profit Calculator: What Do You Keep From Each Order? or the calculator guide.
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