Methodology

Cost per mile (home charging)

cost_per_mile = electricity_rate_$/kWh ÷ vehicle_efficiency_mi/kWh

Electricity rate is pulled from the EIA residential average for the state, or the ZIP-matched utility tariff from OpenEI when available. Vehicle efficiency is EPA combined mi/kWh (or computed from MPGe ÷ 33.7).

Monthly charging cost

We assume 1,000 miles per month of driving unless the user provides their own annual mileage. Monthly kWh ismonthly_miles ÷ mi/kWh; monthly cost is that kWh figure times the chosen rate.

The "mixed" scenario assumes 80% home charging and 20% DC fast-charging at a $0.43/kWh national average — calibrated against published rates from Electrify America, EVgo, and Tesla Supercharger.

Time-of-use savings

Off-peak windows and discount percentages reflect the largest residential EV-specific plan in each state (PG&E EV2-A in California, ComEd Hourly Pricing in Illinois, etc.). Annual savings assume the user shifts ~85% of charging into the off-peak window — a realistic figure for overnight home charging.

Road trip planner

Routes are real driving distances from Mapbox Directions. Charging stops are computed assuming:

• Start at 90% state of charge, arrive at 10%.
• Charging windows are 10% → 80% per stop.
• 12% efficiency penalty for sustained highway speeds.
• Average ~65% of the EV's peak DC rate after taper.

Gas-equivalent cost uses EIA state-average gasoline prices for every state the route passes through.

EV vs gas comparison

Each EV is paired with a similar-class gas vehicle (sedan, SUV, or truck) using EPA combined MPG and a $3.85/gallon US-average gasoline price (overridable by ZIP). Five-year totals use the user's annual mileage and assume rates stay flat — we don't forecast future fuel prices.

How often data updates

• Electricity & gas prices: weekly from EIA.
• Vehicle catalog: monthly, plus on new-model launches.
• NHTSA recalls: daily sync.
• Utility tariffs: quarterly from OpenEI.

What we don't account for

• Demand charges or tiered residential rates (we use the marginal rate).
• Battery degradation over the vehicle's life.
• Charger installation costs (covered separately in our installation cost guide).
• Insurance, registration, or maintenance — fuel only.