Fee Notes
How Shopify fees apply
Shopify's pricing page lists the Basic plan online card rate as 2.9% plus $0.30 USD. This calculator applies that processing fee to total revenue, which on this page means sale price plus buyer-paid shipping.
Shopify's help docs say that when you use Shopify Payments, orders processed through Shopify Payments are not charged third-party transaction fees. That is why the optional 2.0% surcharge should stay off for Shopify Payments orders and only be enabled when you are modeling a third-party gateway scenario.
Shopify's third-party transaction fee page says the billing formula is based on order value including shipping and tax, after discounts. The shared calculator on this site does not yet have separate tax or discount inputs, so this page should be treated as a practical baseline rather than an exact replica of Shopify billing in every edge case.