The wattage of the light fixture can have a much greater impact on the cost than the motor. When calculating the cost to operate a fan with the lights on, you must add the wattage of the lights to that of the motor. The range of wattage for a ceiling fan light fixture is anywhere from 13 watts to 190 watts.alculating the cost to operate a ceiling fan is a simply a matter of knowing how many watts the fan uses and multiplying that by the cost per kWh of electricity you are being charged by your utility company. This will give you the cost per hour to run the fan.