Demurrage F.A.Q.:
What are demurrage charges?:
Demurrage is a fee charged by ocean carriers, trucking companies, and railroads when a container is not removed from the port by the last free day, as allocated in your agreement with the shipper. The demurrage fee and time vary by shipping line. In general, demurrage charges begin to accrue 7 days after your container has been received by the terminal. Demurrage fees are registered daily, for each container in the entry. Therefore a 5 day late entry of 10 containers, charged at $100/day, will cost a total of $5000. Once demurrage fees are imposed, the terminal will not release your container until it is paid. Demurrage charges are most often caused by an untimely filing of the appropriate paperwork (Bill of Lading, Commercial Invoice, Customs Bond, Packing List, and other required paperwork depending on the HTS code of the product). After 10 days of a demurrage, an entry is assigned to a G.O. (government order) warehouse, where it will accrue additional fees and penalties, along with being physically unloaded from a container, increasing the risk of theft & damage to your products.
Demurrage - Everything there is to know about Demurrage. 
can we consider that the demurrage charges is an additional freihgt cost or can we add the demurrage to the freight costs