What is a surcharge?
A surcharge is an extra fee added to a transaction at checkout, on top of the listed price. In resale, it most often refers to a credit card surcharge — a fee added to offset the cost of accepting credit cards.
Surcharging is legal in some states but tightly regulated: a handful of states ban it outright, and where it's allowed, card networks cap it at a percentage of the transaction or the store's actual processing cost, whichever is lower. Given the complexity you should always confirm best surcharge practices for your locale with a professional prior to implementing a surcharge.
A surcharge differs from a convenience fee, which is afee charged for using an alternative payment channel (like paying online with a credit card instead of mailing in a check), and it often applies regardless of the payment type if it is outside standard practice.
Common surcharge mistakes
Surcharging debit cards — prohibited nationwide
Not disclosing the fee at checkout, which most states require
Setting the surcharge above actual processing cost