Shopify doesn’t charge a percentage of your revenue, but there is a fee for processing card payments.

For the Basic $29 USD a month package, Shopify charges a 2.9% +30c credit card processing fee, plus 2% for using a payment processor other than ‘Shopify Payments’.

For the Advanced package, at $299 USD, the processing fee is 2.4% + 30c using Shopify Payments, or + 0.5% for other credit card processing options.