Fuel Cost Calculator

What this computes

Fuel is the cost that's easy to underestimate because it's paid in small, frequent amounts. A $55 fill-up doesn't feel like much; the $2,000+ a year it adds up to does. This calculator makes both the trip number and the annual number visible at once.

Enter your real MPG, local gas price, a trip distance, and your annual mileage. It returns the cost of that trip, the cost per mile, and the full-year fuel bill. Add a second MPG to see exactly what a more efficient vehicle would save you per year — the figure that decides whether the efficient car's price premium is worth it.

The math

It's deliberately simple and exact:

Trip gallons   = trip miles / MPG
Cost per trip  = trip gallons × price
Cost per mile  = price / MPG
Annual cost    = (annual miles / MPG) × price

Cost per mile is the key derived number: it's independent of distance, so it compares any two vehicles or routes directly. The annual figure is just cost per mile scaled by how far you drive in a year.

A worked example

30 MPG, $3.50/gallon, a 120-mile one-way trip, 12,000 miles a year.

• Trip: 120 / 30 = 4 gal × $3.50 = $14
• Cost per mile: $3.50 / 30 ≈ $0.117
• Annual: (12,000 / 30) × $3.50 = $1,400
• A 45-MPG car would cost ≈ $933 — $467/yr less

What matters is gallons per mile, not miles per gallon. That's why 20→30 MPG saves far more than 40→50.

How to use this

1. Measure your real MPG. Divide miles driven by gallons filled over a few tanks. It's almost always below the sticker — budget on the real number.
2. Use cost per mile to compare cars. It strips out trip length and exposes the true efficiency gap between two vehicles.
3. Run the comparison MPG before upgrading. See the annual saving, then weigh it against the price difference and how long you'll keep the car.
4. Plan road trips with the trip figure. Toggle round trip and enter the route distance for an exact fuel line in your travel budget.

The real-MPG gap

The single biggest source of error in fuel budgeting is using the EPA sticker MPG. Real-world economy is typically lower because of:

• Speed. Aerodynamic drag rises with the square of speed; sustained 75+ mph highway driving can cut MPG 10-15% versus the test cycle.
• Short trips and cold starts. An engine is least efficient before it warms up — lots of short trips destroys economy.
• Climate and accessories. Cold weather, winter blends, A/C, and roof/cargo loads all take a measurable bite.

The fix is trivial: use your measured MPG, not the brochure's. A 4-MPG optimism on a 12,000-mile year is roughly $200 of budget that simply isn't there.

What this calculator doesn't model

• Electric vehicles. EV energy is priced per kWh with charging losses, not per gallon. Use the EV Charging Cost calculator.
• Variable MPG within a trip. City vs highway economy differ; this uses one blended figure. For mixed driving, enter a realistic combined number.
• Price volatility. Gas prices move. For an annual budget, use a conservative (higher) price or re-run periodically.
• The rest of ownership cost. Fuel is one line. Depreciation, insurance, and maintenance are the rest — see True Cost of Ownership.