Methodology & data sources
Every number on this site is computed from one open formula set, using public data refreshed on a schedule. Nothing is a black box: the calculator shows each formula with your inputs plugged in, and the full math is below.
Where the data comes from
- Electricity prices — average residential ¢/kWh per state from the U.S. Energy Information Administration (EIA v2 API), refreshed monthly.
- Gasoline prices — regular retail $/gal from EIA, by state where published and otherwise by PADD region, refreshed monthly.
- Vehicle efficiency — EPA combined kWh/100mi (EV) and MPG (gas) from FuelEconomy.gov.
- Utility time-of-use plans — real off-peak/peak rates from the OpenEI Utility Rate Database (URDB), for precision mode.
- Insurance — each state's average full-coverage premium (ValuePenguin / NAIC), with the EV set ~10% above that average and the gas car at ~87% of the EV (EVs cost ~15% more to insure). Registration & incentives — curated state-level estimates, reviewed manually (fully editable). The U.S. DOE Alternative Fuels Data Center (NREL AFDC) can refresh EV registration fees and surface state incentive programs, but the purchase-incentive amount is kept curated on purpose: many state rebates publish an income-qualified maximum (low-income, taxi, or vehicle-replacement tiers) that overstates what a typical buyer receives, so we don't auto-apply it.
Each state carries two dates so freshness is honest: rates updated (the live EIA prices) and fees reviewed (the curated estimates). Site-wide, prices were last refreshed .
Sources & terms. EIA data is used under the EIA API Terms of Service with attribution; EPA/DOE FuelEconomy.gov and DOE AFDC data are public and used under the NLR Developer Network terms (NREL was renamed the National Laboratory of the Rockies in 2026); URDB rate data is Creative Commons Zero. These agencies do not endorse this site. Rates can change — confirm with your utility before deciding.
The formulas
All math lives in one file (costModel.ts)
and is unit-tested against a hand-worked example.
- Annual electricity (kWh)
- annualKWh = (e / 100 × miles) / chargingEfficiency
- Home vs public split
- homeKWh = annualKWh × homeShare ; publicKWh = annualKWh × (1 − homeShare)
- Effective home rate
- TOU ? offpeakShare×rateOffpeak + (1−offpeakShare)×ratePeak : rateHome
- Annual energy cost
- homeKWh × rateHomeEffective + publicKWh × ratePublic
- EV cost per mile
- annualEnergyCost / miles
- Annual gas cost
- (miles / mpg) × gasPrice
- Break-even gas price
- annualEnergyCost / (miles / mpg) — $/gal where the gas car ties the EV on fuel
- 5-yr energy (escalated)
- Σ annualEnergyCost × (1+escalation)^t for t = 0..4
- Operating cost (5 yr)
- energy + insurance + maintenance + registration (no depreciation/incentives)
- EV total cost to own (5 yr)
- depreciation + operating − incentives
- Gas total cost to own (5 yr)
- gasDepreciation + gasFuel + gasInsurance + gasMaintenance + gasRegistration
- Ownership difference
- evTCO − gasTCO (negative ⇒ EV cheaper to own)
- Home L2 charger payback
- (charger + install) / ((ratePublic − rateHomeEffective) × homeKWh)
How depreciation is estimated
Depreciation is the largest single line in 5-year cost and the softest input, so we
make it explicit rather than burying a guess. Each vehicle carries a retention
curve — its residual value as a share of MSRP at the end of years 1–5 —
anchored to iSeeCars' 2025 five-year depreciation study, which puts the
EV average near 58.8% (Tesla Model Y ~58%, Model 3 ~57%, Hyundai Ioniq 5
~59%) versus about 41.5% for all vehicles and 45% for SUVs
— so value-retaining gas SUVs like the Mazda CX-5 (~44%) hold up far better. The 5-year
dollar depreciation is simply
MSRP × (1 − final residual). These are
estimates — verify per trim; the figure is fully editable in the calculator.
| Vehicle | MSRP | Retained (Yr 1 → 5) | 5-yr depreciation |
|---|---|---|---|
| Tesla Model Y | $44,990 | 72% → 61% → 53% → 47% → 42% | $26,094 |
| Tesla Model 3 | $42,490 | 73% → 62% → 54% → 48% → 43% | $24,219 |
| Hyundai Ioniq 5 | $43,975 | 70% → 59% → 51% → 45% → 41% | $25,945 |
| Chevrolet Equinox EV | $34,995 | 68% → 58% → 50% → 44% → 40% | $20,997 |
| Mazda CX-5 | $30,000 | 84% → 76% → 69% → 62% → 56% | $13,200 |
| Nissan Rogue | $30,500 | 80% → 71% → 63% → 56% → 50% | $15,250 |
| Volkswagen Tiguan | $30,000 | 78% → 69% → 61% → 54% → 48% | $15,600 |
| Honda Accord | $28,000 | 80% → 71% → 63% → 56% → 50% | $14,000 |
Depreciation sources: iSeeCars 5-Year Depreciation study and Recurrent (EV-specific resale), 2025. Curves are re-encoded from the latest study when it updates; they remain estimates for comparison, not appraisals.
Financing & used vehicles (optional). Setting a loan APR adds the interest paid within five years to both cars (standard amortization; 0% = cash, the default). “Buy used” reprices the EV from its retention curve at ~3 years old; the next five years' depreciation is extrapolated along the curve's tail (floored at 12%), so used resale beyond year 5 is an estimate.
Default assumptions
Every one of these is editable per calculation.
| Assumption | Default | Note |
|---|---|---|
| Annual mileage | 12,000 mi/yr | US average is ~13k; a conservative round number |
| Charging efficiency | 88% | AC wall→battery losses |
| Home charging share | 80% | rest is public DC fast charging |
| Public DCFC rate | $0.45/kWh | blended fast-charge price |
| Energy price escalation | 0%/yr | off by default; wired for future use |
| L2 charger + install | $500 + $800 | typical home Level-2 setup |
| Gas insurance | 87% of EV insurance | EVs cost ~15% more to insure |
| Gas registration | $50/yr | base registration, no EV road-use fee |
Precision mode: your utility’s time-of-use rates
By default, charging uses each state’s average residential rate. For
18 major utilities you can switch to your utility’s real
time-of-use plan — off-peak and peak prices pulled from the
OpenEI URDB
and refreshed monthly — so the estimate reflects scheduled overnight charging
instead of a flat average. The off-peak charging share is a behavioral
assumption (default 85%),
editable in the calculator. Pick your plan in the calculator’s Precision
panel; the effective rate is
offpeakShare × offpeak + (1 − offpeakShare) × peak.
Limitations & caveats
- Depreciation is an estimate and is usually the largest single line in 5-year cost — it dominates the EV-vs-gas verdict. We show the data-backed operating subtotal separately so you can judge it apart from resale guesswork.
- The federal EV tax credit ended September 30, 2025. Seed data therefore assumes $0 federal and reflects state-only incentives, which often have income or price caps. Verify current programs before buying.
- Gas insurance and registration are derived (87% of the EV insurance figure, and a flat $50/yr with no EV road-use fee) rather than measured per state.
- Prices are state averages by default. Precision mode pulls real time-of-use plans from the URDB for 18 major utilities (more over time); other utilities can be modeled manually.
These are estimates for comparison, not quotes. Confirm with your utility, insurer, and state DMV before making a decision.