Per diem is the daily rental price of the container after the free days (usually 3-5) have passed and the container is away from the port or container yard. The per diem varies depending on container type and is negotiable for each deal. Per diem is another word for detention.
With per diem charges, carriers incentivize importers and exporters to return containers on time for loading, because their business model is to move cargo from port to port. That’s why carriers want to keep their equipment in circulation and avoid injection of additional equipment into the fleet or chassis pool.
Per diem charges quite often exceed hundreds of dollars, costs that could be easily avoided with better planning, good preparation (drayage scheduling, customs clearance preparation of documents and the container itself) or SOC containers. Because you don’t always have delays in your own hands with for instance congested ports and the lack of truck drivers, SOC containers increase your flexibility and reduce per diem costs.
Moreover, you can negotiate extended free days with your carrier (usually if you move more than 1000 TEUs/ year), setup the delivery schedule with your truckers in advance and make sure your warehouse is prepared to load/ unload the cargo.