How This Calculator Works
This tool computes a side-by-side monthly cost comparison between your current gas
car and one or more prospective vehicle purchases — hybrid, plug-in hybrid (PHEV),
or EV. Pick the types you're considering and each one becomes its own column in the
results. It goes beyond simple fuel savings by factoring in your existing car payment,
trade-in value, financing, state taxes, registration fees, oil changes, and home
charger installation where applicable.
All math runs entirely in your browser — nothing you enter is sent to a server.
Results update in real time as you fill in the fields.
What Is the Breakeven Period?
The breakeven period is the number of months it takes for monthly savings from the
new vehicle to fully offset its upfront costs (down payment, home charger where
applicable, and sales tax).
For example: if the new vehicle saves you $150/month but required $9,000 upfront,
your breakeven point is 60 months (5 years). After that point, every month of
ownership represents a net financial gain compared to keeping your gas car.
If the new vehicle costs more per month than your gas car, there is no breakeven —
it costs more both upfront and ongoing.
How Fuel & Electricity Costs Are Calculated
Gas monthly fuel cost: (yearly miles ÷ 12) ÷ MPG × gas price per gallon
Monthly electricity cost: (yearly miles ÷ 12) ÷ efficiency (mi/kWh) × electricity rate ($/kWh)
For a plug-in hybrid we estimate the share of miles driven on battery from your
typical daily commute and the vehicle's EPA electric range: if your daily drive is
under the electric range, essentially every mile runs on electricity; longer daily
drives fall back to the gas engine for the remainder.
The average US household drives about 15,000 miles per year. With a 25 MPG car at
$3.50/gallon, that's roughly $175/month in fuel. A hybrid at 50 MPG cuts that in
half; a comparable EV at 3.5 mi/kWh and $0.14/kWh would cost about $50/month.
How Loan Payments Are Calculated
Monthly loan payment uses standard loan amortization:
M = P × [r(1+r)^n] / [(1+r)^n − 1], where P is the principal
(purchase price minus down payment and trade-in value), r is the monthly interest
rate (APR ÷ 12), and n is the number of months.
Your current car's trade-in (KBB) value is subtracted from each prospective
vehicle's purchase price before financing, reducing the amount you need to borrow —
even a modest trade-in can meaningfully lower your monthly payment.
State Taxes & Registration Fees
When you select your state, the calculator automatically applies your state's vehicle
sales tax rate to the purchase price, adding it to your upfront costs. Most states
charge between 0% (Alaska, Delaware, Montana, New Hampshire, Oregon) and 9%+ sales tax.
Many states also charge annual EV registration surcharges — sometimes called "road
use fees" — to offset the fact that EV drivers don't pay gas taxes. These fees
typically range from $50 to $200+ per year and apply to pure EVs only in this
calculator. Plug-in hybrids and hybrids are treated as exempt as a first-pass
approximation; some states do charge reduced PHEV fees in practice.
Tips for Accurate Results
- MPG: Use the EPA combined rating for your specific model year, found at fueleconomy.gov.
- Gas price: Use your local average, which can vary significantly by state and season.
- EV / PHEV efficiency: Find the EPA-rated kWh/100 mi on the window sticker, then convert: miles per kWh = 100 ÷ kWh/100mi.
- PHEV electric range: Use the EPA electric-only range (not total range).
- Daily driving: For PHEVs, be honest about your typical daily miles — this controls how often the battery covers your trips.
- Electricity rate: Check your utility bill for your actual rate. Time-of-use rates for overnight charging can be much lower than your daytime rate.
- KBB value: Enter your car's trade-in value from kbb.com or a dealership quote — this directly reduces the financed amount.
- Home charger: A Level 2 (240V) home charger typically costs $800–$1,500 installed. Some utilities offer rebates.
What This Calculator Doesn't Cover
This tool focuses on the financial comparison most relevant to a purchase decision.
It does not model insurance costs (which vary widely), general maintenance beyond
oil changes, tire wear, battery degradation over time, federal or state EV tax
credits, hybrid/PHEV incentives, or resale value differences.