49 CFR §375.703

1. (a)On a binding estimate, the maximum amount is the exact estimate of the charges, plus charges for any additional services requested by the shipper after the bill of lading has been issued and charges, if applicable, for impracticable operations as defined in your carrier tariff. The maximum amount of charges for impracticable operations you may collect on delivery is an amount equal to 15 percent of all other charges due at delivery.
2. (b)On a non-binding estimate, the maximum amount is 110 percent of the non-binding estimate of the charges, plus charges for any additional services requested by the shipper after the bill of lading has been issued and charges, if applicable, for impracticable operations as defined in your carrier tariff. The maximum amount of charges for impracticable operations you may collect on delivery is an amount equal to 15 percent of all other charges due at delivery.