Write down every load’s nominal power.
The reason we don't just add every circuit's maximum capacity is . It is highly unlikely that every light, toaster, air conditioner, and EV charger will be running at 100% capacity at the exact same moment. Maximum demand calculators apply "diversity factors" to different load groups to account for this reality. Methods of Determining Maximum Demand
Maximum Demand is the highest average load (usually measured over 15, 30, or 60-minute intervals) that a system draws during a billing period.