How this instrument works
A plug-in hybrid electric vehicle (PHEV) runs on battery power for a limited electric-only range and switches to its gasoline engine once the battery depletes, which means its real-world cost per mile depends heavily on what fraction of total driving happens on each power source — a PHEV driven mostly on short trips that stay within electric range costs very differently to run than the same vehicle used mainly for long highway drives that quickly exhaust the battery.
Quoting a single MPG or MPGe figure in isolation hides that split. This calculator instead computes the cost per mile for electric driving and gasoline driving separately, then blends them by the percentage of miles actually driven on each — the same approach fuel-economy labeling for plug-in hybrids uses, since neither the electric-only nor gas-only figure alone represents what an owner actually pays per mile.
The blended figure is sensitive to both the electric/gas driving split and to local electricity and gasoline prices, which is why the same PHEV can show meaningfully different real-world cost per mile for two different owners with different commuting patterns and different regional energy prices — there's no single 'true' number independent of how and where the vehicle is actually driven.
- Enter Miles driven on electricity (%) and Miles driven on gasoline (%) — your best estimate of the driving split; they don't have to sum to exactly 100 if some driving happens off-grid or is uncertain.
- Enter Electricity price ($/kWh) and Electric efficiency (mi/kWh) — from your utility bill and the vehicle's EPA electric efficiency rating.
- Enter Gasoline price ($/gal) and Gas mileage (mpg) — local pump price and the vehicle's EPA gasoline-mode rating.
- Read Blended cost per mile ($) — the combined, realistic cost per mile across both power sources at your actual driving split.
Worked example — 70% electric, 30% gas driving
A PHEV owner drives 70% of miles on electricity at $0.13/kWh and 3.5 mi/kWh efficiency, and 30% on gasoline at $3.50/gal and 40 mpg. Electric-mode cost is 0.13/3.5 = $0.037143/mile; gas-mode cost is 3.50/40 = $0.0875/mile.
Blending by driving share: 0.7 × 0.037143 + 0.3 × 0.0875 = 0.026 + 0.02625 = $0.05225 per mile. That's meaningfully cheaper than the vehicle's gas-only cost of $0.0875/mile, reflecting how much of this owner's driving actually happens on cheaper electric power rather than gasoline.
Questions
Why does the blended cost matter more than the MPGe sticker figure?
MPGe is calculated under a standardized test cycle that assumes a specific electric-versus-gas driving split, which rarely matches any individual owner's actual habits — someone who never charges and drives mostly on gasoline gets a very different real cost per mile than someone who charges nightly and rarely exceeds electric range. Blending your own driving percentage with your own local prices gives a far more accurate personal cost estimate.
How do I estimate my own electric-versus-gas driving percentage?
Many PHEVs display this directly in an onboard trip computer or companion app, tracking electric miles versus gasoline miles over recent trips or the vehicle's lifetime. Without that data, a reasonable estimate comes from comparing your typical daily driving distance against the vehicle's rated electric-only range and how consistently you charge between trips.
Why is electric mode usually so much cheaper per mile than gasoline mode?
Electricity is typically cheaper per unit of usable energy than gasoline at current US prices, and electric motors convert that energy to motion far more efficiently than a gasoline engine converts combustion heat to motion — the combined effect is that electric-mode cost per mile commonly runs a third to a half of gasoline-mode cost per mile for the same vehicle, though the exact gap depends heavily on local electricity and gas prices.
Does this account for the extra cost of a home EV charger or electricity demand charges?
No — this calculates only the direct energy cost per mile from a straightforward electricity price and efficiency figure, not one-time equipment costs like installing a home charger, or utility rate structures like time-of-use pricing or demand charges that some households face. Entering an average effective electricity price that reflects your actual charging costs will produce a more accurate blended figure.
How does this differ from a full electric vehicle's cost per mile?
A fully electric vehicle has no gasoline mode at all, so its cost per mile is simply the electric-mode calculation with the gas percentage effectively at zero — setting Miles driven on electricity (%) to 100 and gasoline to 0 here reproduces that all-electric cost per mile, letting you compare a PHEV's realistic blended cost directly against what a comparable full EV would cost to run.