An electronic pool pump timer that controls the run time or the pump for a period of time each day depending on the date. In the preferred embodiment, the user enters the historical daily maximum and minimum pump run times for the specific pool and the system calculates the required time the pump will run on a given day. The customized run time is thus calculated as a function of the date and the minimum and maximum run times for a given pool. The system then self-adjusts the run time each day as necessary. The device comprises a data input means, a display, memory, and a controller. It may also include a manual override to allow the user to turn the pump on at any time. The device is connected to the pump motor. The device is connected to a power supply and may also include a battery back-up in the event of a power outage. To prevent the pool from freezing. the system may also include an air temperature sensor that triggers pump operation when the ambient air is below a given temperature.