100 Amp vs 200 Amp: Do You Need the Upgrade?
200-amp service is the modern residential standard and what most electricians recommend for any home adding an EV charger, heat pump, or addition. Many 100-amp homes are fine as-is if loads are modest and the panel has space. The deciding tool is the NEC load calculation: if your calculated load exceeds 80 percent of service capacity, or a planned addition pushes it there, upgrade.
100 amps was plenty when houses had a refrigerator, a TV, and incandescent bulbs. Then came the EV charger, the heat pump, the induction range, and the home office full of equipment. This guide explains how to know whether your 100-amp service still suffices or the upgrade is due.
What 100 amps actually supports
A 100-amp, 240-volt service delivers 24,000 watts of capacity. That sounds like a lot until you add it up: electric range (40-50A), electric dryer (30A), central air (20-30A), electric water heater (25-30A). A 100-amp home with gas heat, gas water heating, and gas cooking can run comfortably for decades. The same service with electric everything is already tight, and adding any single 40 to 60 amp load (EV charger, heat pump, hot tub) pushes it over. The question is never just the number on the main breaker; it is the sum of what is connected to it.
The load calculation: the real answer
The National Electrical Code (Article 220) defines how to calculate a dwelling's load: general lighting and receptacles at 3 watts per square foot, fixed appliances at nameplate rating, HVAC at the larger of heating or cooling load, all with prescribed demand factors. An electrician runs this in under an hour. If the calculated load is under 80 amps on a 100-amp service, you have headroom. If it is at or over 80 amps, or a planned addition (EV charger at 48A continuous, for example) pushes it there, the upgrade is not optional; it is code. Ask for the calculation in writing; it is the difference between a sales pitch and an engineering answer.
Signs you have outgrown 100 amps
Breakers tripping when two large loads run together. The panel is full with no spaces for new circuits. You are planning an EV charger, heat pump, induction range, hot tub, or addition. The home still has 60-amp service with fuses (upgrade regardless). Lights dim when the air conditioner starts. Any one of these warrants the load calculation; two or more usually mean the upgrade decision is already made.
What the upgrade involves
A 100-to-200-amp upgrade is a service upgrade, not just a panel swap: new service-entrance conductors sized for 200A, usually a new meter socket, sometimes a new mast or weatherhead, the 200-amp panel with a full breaker set, grounding and bonding updates, permit, inspection, and utility coordination for the disconnect/reconnect. The power is off for several hours during the cutover; plan accordingly. Typical cost $1,300 to $2,000 for a standard job, more with underground service or difficult access.
When 100 amps is fine
Stay at 100 amps if the load calculation shows headroom, the panel has free spaces, the panel itself is a modern brand in good condition, and you have no electrification plans. Gas-heated homes with modest electrical loads can run on 100 amps indefinitely. Spending $2,000 to upgrade capacity you will never use is not an investment; it is a donation to the electrician's boat fund.
The bottom line
Get the NEC load calculation before deciding anything. If it shows headroom and your plans are modest, 100 amps is fine. If you are adding any 40-plus-amp load or the panel is obsolete, the 200-amp upgrade ($1,300 to $2,000) is the standard, correct move, and doing it before the EV charger arrives is cheaper than doing it as an emergency change order.
Figures current as of October 2026. Sources: HomeGuide and contractor-published 2026 cost guides; CPSC documentation on Federal Pacific panels.