EV Charger Cost and Circuit Calculator

How the calculator works

An EV charger can run for hours at full power, so the electrical code treats it as a continuous load. The breaker must be at least 125% of the charger's maximum current (NEC 625.41 and 625.42, with 210.19(A) and 210.20(A)). The tool multiplies your charger amps by 1.25 and rounds up to the next standard breaker size from NEC 240.6(A). For example, 40 A x 1.25 = 50 A.

Next it picks the smallest copper wire whose ampacity in NEC Table 310.16 is at least the breaker size. The main result uses the 75 C column, which fits THHN/THWN-2 wire in conduit when the breaker and charger terminals are rated 75 C (NEC 110.14(C)). Most are, but check the labels. NM-B cable (the common plastic-jacketed house cable) must use the 60 C column (NEC 334.80), so it often needs one size larger. The small-wire limits in NEC 240.4(D) also apply (12 AWG on 20 A, 10 AWG on 30 A).

The tool also estimates voltage drop on your run: 2 x 12.9 x amps x feet, divided by the wire's area in circular mils, as a percent of 240 volts. The NEC only suggests about 3% in an informational note, so a higher number is a reason to look at a bigger wire, not a rule.

What changes the answer

Distance and location change the wire and the cost. A long run can push voltage drop over 3%. A detached garage or an outdoor spot usually means conduit, trenching or wire rated for wet places, and NM-B cable is not allowed in wet or damp locations (NEC 334.12).

Panel room matters most. The panel check is a rule of thumb: a 100 A panel with a 40 A or larger EV circuit, a 125 or 150 A panel with a 60 A circuit, or any panel of 60 A or less gets a "may need a panel upgrade" flag. Only a load calculation (NEC 220.83 for an existing home, or 220.87 using a year of meter data) can tell for sure. If the panel is tight, many chargers can be set to a lower current, and an energy management system can share capacity (NEC 625.42).

Many chargers let the installer set the max current with a dial or an app. Set the calculator to the current the charger will be set to, not the biggest number on the box.

How the cost range works

The install range comes from a set of published market prices, not a quote. A charger in an attached garage within 25 feet of the panel uses the "near the panel" range. Anything farther, in a detached garage or outdoors uses the "long run" range. The 25 foot cutoff is our planning assumption. The charger unit is shown on its own line because many owners buy it themselves.

The range does not include a panel or service upgrade, drywall patching or painting. Permit fees vary by place.

Monthly charging cost

The optional cost line is miles per month x your car's kWh per 100 miles, divided by 100, x your electricity price. The kWh per 100 miles figure is on the car's EPA label and on fueleconomy.gov; most 2026 electric cars listed there use about 23 to 39 kWh per 100 miles, and 32 is a middle value. The default price, 16.95 cents per kWh, is the Virginia residential average for January to August 2026 from the U.S. EIA (preliminary data). Type in your own rate for a better estimate.

When to call an expert electrician

Call one before you buy a charger if your panel is 100 A or smaller, has no open breaker spaces, or the run goes outside or underground. An expert electrician does the load calculation, checks the terminal ratings, picks the wiring method and handles the permit and inspection where one is required.