Percentage Price Field

This extension allows you to add an "Additional Percentage" field to any price set, which will automatically calculate and add an additional amount to a transaction, as a configurable percentage of other selected price set options.

E.g.,

• Ask donors to give an extra 3% to cover credit card processing fees
• Ask them to give an additional 10% of their membership fee to support a special project

https://civicrm.org/extensions/percentage-price-field