Consider it when the combined loads — a Level 2 charger or two, a heat pump with backup heat, and an accessory dwelling unit — will not fit a single 200-amp service after a real load calculation. Do not start there because the numbers sound more future-proof. Fixr’s electrical-panel upgrade guide, updated 31 January 2025, treats 300- and 400-amp services as uncommon residential work and publishes $3,500–$7,500 to upgrade to 300 amps and $8,000–$12,000 to upgrade to 400 amps (labor included). Angi, updated 29 October 2026, publishes a lower 400-amp panel-plus-install band of $2,000–$4,000, which does not match Fixr and is another reminder that scope and date matter. Fixr also notes two paths to 400 amps: one 400-amp panel, or a pair of 200-amp panels, the second sometimes using more readily available equipment.
| Source | As-of date | Published range |
|---|---|---|
| Fixr, upgrade to 300 A | 31 Jan 2025 | $3,500–$7,500, labor included |
| Fixr, upgrade to 400 A | 31 Jan 2025 | $8,000–$12,000, labor included |
| Angi, 300 A panel + install | 29 Oct 2026 | $1,800–$3,500 |
| Angi, 400 A panel + install | 29 Oct 2026 | $2,000–$4,000 |
Utility rules, transformer capacity, and the path of the service lateral often decide the architecture as much as the panel shop. Have the electrician and the utility talk before you fall in love with a 400-amp can. Put the house, the charger, the heat pump, and the ADU on one planning sheet first — the calculator can hold the house-side numbers — and treat 400 amps as a solution to a documented problem.
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.