A surcharge is a charge that is added on to an existing charge or payment that is required to be paid from one party to another.
Surcharges are often included as a penalty for a certain action, or because the initial charge left out the extra charge, which is added on later as the surcharge.
In the context of the law, surcharges often must be paid for the particular transaction to go through legally.
In many situations, surcharges can be added if a payment is not made on time. For example, a mortgage borrower may be forced to pay a surcharge if they pay their mortgage payment late.
Even though surcharges are not technically part of the original charge, they still are typically legally enforceable. This is especially true if there is a contract that states that surcharges may apply under certain circumstances. A person who does not pay required surcharges can face even more penalties.