Tracking Fuel Costs: Gas, Diesel, and EV Charging

Updated 2026-07-28

A gallon of gas, a liter of diesel, a kilowatt-hour of electricity — none of them cost the same, and none of them answer the question that matters: how much is this car costing you to drive. That gap gets wider in a household with more than one powertrain, where one car's receipts show up in gallons and the other's cost is buried in the electric bill. Comparing them side by side means converting everything to one number, and remembering to log the EV charge as carefully as the gas fill-up in the first place.

Different units, same question

Gasoline and diesel show up at the pump as a price per gallon or per liter, and comparing them looks simple at first: read the sign, do the math, fill the tank. Diesel usually costs more per gallon than gasoline in many regions, but diesel engines typically return better fuel economy, so a higher price at the pump does not always mean a higher cost per mile. You only see that once you compare cost per mile rather than cost per gallon or per liter — a car that looks expensive to fill can still be cheap to drive, and the reverse is also true. Rated fuel economy numbers are also a starting point, not a guarantee: a car driven mostly on the highway and a car driven mostly in stop-and-go traffic can post very different real-world MPG even with the identical engine, so the number on a window sticker only goes so far. Tracking the two figures side by side, fill-up after fill-up, over months rather than one tank, is the only way to know which is happening for your specific car rather than guessing from the price on the sign or the rating on a spec sheet. The same logic applies whether the car is used for a daily commute or occasional weekend trips — the pattern only shows up once there is more than one entry to compare it against.

Electricity is priced per kilowatt-hour instead of per gallon, and that rate depends heavily on where the charge happened. Charging at home overnight on a household electricity rate is usually the cheapest way to add range, while a public rapid charger on a road trip often costs noticeably more per mile for the same car. A home charge also does not come with a receipt the way a gas station does — it is buried inside a monthly electricity bill alongside everything else the house runs on, which makes it easy to skip logging altogether. Efficiency shifts too: cold weather, highway speeds, and heavy use of climate control can all pull more energy per mile out of an EV, the same way stop-and-go traffic pulls more fuel out of a gas engine, so a single charging session tells you less than a running record does. None of this requires precision down to the last cent. What it requires is consistency — logging every charge the way you would log every tank of gas, so the running total reflects how the car is used in practice rather than a handful of remembered numbers. Estimating the cost of a single charging session and logging it anyway, even from a rough calculation based on the electricity rate on your bill, gives you a real number to compare against gas or diesel instead of no number at all.

What to log at every fill-up or charging session

• Odometer reading at the time of the fill-up or charge, so cost-per-mile math has a real distance to divide into instead of a guess
• Total amount paid, not the price per unit alone — taxes, fees, and rounding all change the real number
• Date, so you can see cost move over time and catch seasonal swings in gas or electricity pricing before they surprise you at the pump or on the bill
• Where you filled up or charged — home, a specific station, a public fast charger — since home and public charging often cost noticeably different amounts per mile
• A note on anything unusual, like a discount, a borrowed car, or a one-off road-trip charger, so it does not skew your average later
• How you're paying, if it matters to your budgeting — a home electricity bill often covers weeks of driving at once, while a gas receipt covers a single tank

One view across a mixed-powertrain household

CarCare's fuel log is built around fill-ups and MPG, which maps directly onto gasoline and diesel: log the odometer reading and the amount paid at each fill-up, and the app tracks MPG and fuel cost over time on the Family plan, building the record entry by entry instead of in a separate spreadsheet. For an EV in the same household, log the charging cost the same way, but through Expense tracking, part of the same Family plan, where cost-per-km analytics roll fuel up alongside service, insurance, and tires into one total cost of ownership per car. Because CarCare supports multiple cars with their own reminders and history, a gas sedan and an EV hatchback each build a separate cost-per-km trend over time, and the car selector switches between them without mixing one car's numbers into the other's.

CarCare does not provide legal, insurance, traffic, or mechanical advice. Always confirm deadlines and requirements with your owner's manual, a qualified mechanic, or your local authority.