Terms and Definitions

FOB: this term which stands for free on board, refers to all costs incurred to bring the goods or items of import to the terminal for shipment. FOB = Total Ancillary Charges + Total Value of Goods. The pro forma invoice always states what the FOB value is.
Freight Cost: this is the estimated cost of transporting item from the terminal in the supply country to the port in the destination country.
Insurance: by this we mean the premium paid to the insurance company for issuing marine certificate or insurance certificate to the importer. Each insurance company has its premium rate, which must be agreed with the importer. Insurance = [FOB + Freight + 10% (mark-up)]*Premium rate. No worry about this, an example will clarify the matter just keep reading.
CIF: this stands for Cost Insurance and freight. CIF = FOB Value + Insurance Value +Freight Value
Surface Duty (ID): this is often commonly referred to as import duty, which is how the abbreviation – ID came about. Its duty based on the kind of item imported. The value depends on the HS Code – usually 5%, 10%, 20%, etc. of the CIF Value. ID = x% of CIF Value.
Surcharge: this is an additional tax levied on importation of goods, and meant for port development. Surcharge = 7%*ID.
CISS: this stands for Comprehensive Import Supervision Scheme. CISS = 1%*FOB Value.
ETLS: This means ECOWAS Tax Liberalisation Scheme often referred as ECOWAS levy for short. It is tax imposed on goods imported from non-ECOWAS member countries into ECOWAS member country. The monies so raised is used to run the commission’s office and for community development. ETLS = 0.5%*CIF.
VAT: Value Added Tax is tax for value addition or services rendered. VAT = 5%*(CIF+ID+Surcharge+CISS+ETLS).
Example Duty Estimation or Calculation
http://www.clearingandforwardingnigeria.com/how-to-estimate-import-duty-and-clearing-cost-in-nigeria/