Customers are usually charged a monthly service fee and additional charges based on the electrical energy (in kWh) consumed by the household or business during the month. Commercial and industrial consumers normally have more complex pricing schemes. These require meters that measure the energy usage in time intervals (such as a half-hour) to impose charges based on both the amount of energy consumed and the maximum rate of consumption, i.e. the maximum demand. This is usually called peak demand charge. Frequent reporting also allows the retailer to pass on the spot price (with some markup) to its customers.