An electric oven is a box of heating elements. Bake and broil elements are often 2,000–3,500 watts. Preheat is not free: the empty box has to reach temperature before food goes in. Opening the door mid-bake dumps heat you then pay to put back.
The myth is that the oven light or a peek “doesn’t count.” The peek is a few minutes of recovery heat. Forgetting an empty preheat for 20 minutes is a real extra run. A long roast is hours at that wattage, not a single spike.
Self-clean cycles are a different, hotter program. If you use one, treat it as its own long, high-watt event — not a regular bake.
Whatt prices the hours you set at the wattage for bake or broil. What-ifs cover a door peek, extra bake time, and an empty preheat left on.
At 18.8¢ per kWh, 2,500 watts for 1 hour is about 0.47. Twenty extra minutes is about 0.16. That is the element, not the kitchen’s AC working harder because you heated the room.
Gas oven
If the oven is gas, use Gas stove and the oven-bake setting. This page is electric elements in a box.
Related
Usage estimate only — not a utility bill, load calc, or advice.