PHEV Economy Calculator
Blended MPGe, monthly energy cost, and cost-per-mile split for your plug-in hybrid — from your own electric miles (kWh) and gasoline use. This is a calculator, not a unit converter: it blends two energy sources, compares against a gasoline-only car, and estimates payback on the PHEV price premium.
Your driving & prices
Estimates are computed from your inputs only — not an EPA rating of any specific vehicle. Uses the EPA energy equivalence of 33.7 kWh per gallon of gasoline.
Results
Energy breakdown
| Electricity used | – |
| Electric energy as gallon-equivalents (kWh ÷ 33.7) | – |
| Gasoline burned | – |
| Total gallon-equivalents | – |
| Total miles | – |
Cost breakdown
| Electricity cost / month | – |
| Gasoline cost / month | – |
| Total energy cost / month | – |
| Cost per mile — blended | – |
| Cost per mile — electric miles | – |
| Cost per mile — gas miles | – |
vs gasoline-only car
| Gas-only car cost / month (same miles) | – |
| Monthly savings | – |
| Annual savings | – |
| Price-premium payback | – |
Payback = premium ÷ annual savings (simple, undiscounted). Negative savings mean the PHEV costs more to fuel than the comparison car at these prices — charging habits and rates drive the outcome. Charging losses (~10–15% wall-to-battery) are not included.
How it works
Blended MPGe = total miles ÷ (kWh ÷ 33.7 + gallons of gasoline). Example with the defaults: 270.00 kWh ÷ 33.7 = 8.012 gallon-equivalents of electricity, plus 2.500 gallons of gasoline = 10.512 gal-eq total; 1000 miles ÷ 10.512 = 95.1 MPGe. All figures are estimates from your inputs.
Frequently asked questions
What is MPGe and why does this calculator use 33.7?
MPGe (miles per gallon equivalent) measures how far a vehicle travels per unit of energy equal to one gallon of gasoline. The U.S. EPA defines 1 gallon of gasoline as containing 33.7 kWh of energy, so electric energy is converted with gal-eq = kWh / 33.7 before being added to the gasoline gallons you burn. This is an energy-equivalence definition, not a rating of any specific vehicle.
How is blended MPGe calculated for a plug-in hybrid?
Blended MPGe = total miles / (kWh/33.7 + gallons). Example: 900 electric miles at 30 kWh/100 mi uses 270.00 kWh = 8.012 gallon-equivalents; 100 gas miles at 40 MPG burns 2.500 gallons. Total: 1000 miles / (8.012 + 2.500) = 1000 / 10.512 = 95.1 MPGe. The more miles you drive on electricity, the higher the blended number.
How much does each mile cost on electricity versus gasoline?
Using the default example: electricity costs $40.50 for 900 miles = $0.0450 per mile, while gasoline costs $8.75 for 100 miles = $0.0875 per mile. Electric miles cost roughly half as much per mile at $0.15/kWh and $3.50/gal — but flip the prices (expensive electricity, cheap gas) and the advantage can disappear, which the calculator shows honestly.
How much can a PHEV save versus a gasoline-only car?
The comparison car drives your same total miles at its own MPG. Example: 1000 miles at 30 MPG and $3.50/gal costs the gas car $116.67/month, while the PHEV costs $40.50 + $8.75 = $49.25/month. Monthly savings: $116.67 - $49.25 = $67.42, or $809.00 per year.
How long does it take to pay back the PHEV price premium?
Payback (years) = price premium / annual fuel savings, simple and undiscounted. Example: a $4000 premium divided by $809.00/year of savings = 4.9 years. If electricity is expensive or you rarely charge, annual savings shrink and payback stretches — or never arrives, in which case the calculator shows no payback period.
Why does my electric share of driving matter so much?
Because electric miles are usually far cheaper per mile. In the default example, 90.0% of miles run on electricity, giving 95.1 MPGe and $809.00/year in savings. A balanced 50/50 split (500 EV + 500 gas miles) drops to 55.8 MPGe and $479.40/year in savings with a 10.4-year payback. Charging habits drive the economics more than any other input.
What happens if I drive a whole month on electricity only?
With 0 gas miles, blended MPGe equals your pure electric efficiency: 1000 miles on 300.00 kWh = 300/33.7 = 8.902 gal-eq, so 1000/8.902 = 112.3 MPGe. Conversely, a month with 0 electric miles collapses blended MPGe to your gasoline MPG (40.0 in the example) — the calculator then behaves like a plain MPG cost calculator.
Is this an official EPA fuel-economy rating?
No. EPA window-sticker ratings come from standardized lab tests of a specific vehicle. This tool estimates YOUR real-world result from YOUR driving split, efficiency, and local energy prices. Treat every output as an estimate based on your inputs, not a certified rating.
Does the calculator include charging losses?
No — it assumes the kWh you enter (or derive from kWh/100 mi) is the energy used by the car. Real wall-to-battery charging loses roughly 10-15% as heat, so your true electricity cost is slightly higher than shown. To account for it, increase your kWh/100 mi input by about 10-15%.
How is this different from a fuel economy unit converter?
A unit converter (like our fuel-economy-converter) only translates between MPG, L/100km, and km/L — pure unit math with no electricity involved. This is a calculator: it blends two energy sources into one MPGe figure, splits monthly costs between electricity and gasoline, compares against a gas-only car, and estimates payback on the PHEV price premium.
Free tool by NRTechStudio