Abstract: The multi-day programmable hot water heater controller employs a control circuit, in communication with a temperature sensor and a switching device, to control the operation of a water heater. The temperature sensor is attached to a water heater, positioned where the water temperature within the water heater can best be read. Temperature loss between the water and the temperature sensor may be determined by calculation or measurement, and corrected by the control circuit. The multi-day programmable hot water heater controller monitors water temperature within the water heater, and controls the switching device to switch the water heater on or off, maintaining the water temperature according to programmable parameters. Users program the multi-day programmable hot water heater controller to define periods during which the water heater is operated to maintain a desired water temperature. At other times, the water heater is turned off to conserve energy.