It is a written estimate of how much load the service or feeder must be able to carry after the charger is added. Electricians use the dwelling-unit methods in the adopted National Electrical Code (Article 220 in the 2023 edition, Article 120 in the 2026 edition) or, for many existing houses, measured utility demand. Inspectors often want to see that calculation with the permit. Counting open slots is not a load calculation.
Two paths show up over and over in permit checklists and in homeowner threads:
- Measured demand (often the better fit for an existing house): take 12 months of peak demand, multiply by 125%, add the new EV load, and compare with the service rating.
- Calculated method (standard or optional): start from floor area, required circuits, and appliance nameplates, apply the code’s demand factors, then add the charger as that edition requires.
This site’s calculator offers an educational version of (1) and a simplified version of the optional method in (2). It does not reproduce copyrighted NEC tables and it is not the form your inspector will stamp. The all-gas 1,800 ft² worked examples on the 100-amp pages (about 71.0 A with a 32 A charger in that narrow example) exist only to show the arithmetic, not to clear your house. Bring nameplates and, if possible, utility demand data to a licensed electrician.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.