Enter your oven's wattage and total cooking time (including preheat) to see the real cost per use.
An oven's heating element cycles on and off to maintain temperature rather than running continuously — duty cycle accounts for that, so actual cost is meaningfully less than nameplate wattage times full runtime.
An oven's thermostat cycles the heating element on and off to hold a set temperature rather than running full-power the entire time, so using the full nameplate wattage for the whole cook time would significantly overstate the real cost. A 60% duty cycle is a reasonable default for maintaining temperature after preheat; convection ovens with fans often run slightly more efficiently at a lower duty cycle.
Often somewhat, yes — the fan-assisted heat distribution can allow slightly lower temperatures or shorter cook times for the same result, modestly reducing total energy used.
Preheat uses the element at closer to full duty cycle since it's working hardest to reach temperature quickly — for short cook times, preheat can represent a meaningful share of the total energy used for that meal.