Cost Calculator AI
Cars & VehiclesHarmonic Mean Model

Annual Car Fuel Cost Calculator

Calculate your annual gasoline budget using mathematically accurate harmonic-mean combined city and highway MPG, annual mileage, and pump prices.

Calculation Results

Harmonic Mean Combined Fuel Economy Formula

Combined MPG = 1 / [ (City Fraction / City MPG) + (Highway Fraction / Highway MPG) ]
  • Harmonic Mean Principle: A simple arithmetic average of MPG produces false fuel savings. Fuel consumption is inversely proportional to MPG, requiring a harmonic mean.
  • Annual Fuel Cost = (Annual Miles / Combined Harmonic MPG) × Gas Price per Gallon.
  • 5-Year Fuel Expense = Annual Fuel Cost × 5.

Step-by-Step Worked Example

Scenario: Driving 15,000 miles/year with a 60% city / 40% highway split (22 City / 32 Hwy MPG) with gas at $3.50/gal

Calculation Steps:

  1. Harmonic Denominator = (0.60 / 22) + (0.40 / 32) = 0.02727 + 0.01250 = 0.03977
  2. Blended Combined MPG = 1 / 0.03977 = 25.14 MPG
  3. Annual Gallons = 15,000 / 25.14 = 596.66 gallons
  4. Annual Fuel Cost = 596.66 × $3.50 = $2,088.31
  5. Monthly Fuel Budget = $2,088.31 / 12 = $174.03 / month
Result: Your blended fuel economy is 25.1 MPG, costing $2,088.31 per year ($174.03/month).

How to Use This Calculator

  1. 1Enter your anticipated annual driving mileage.
  2. 2Specify your typical city driving percentage (e.g. 55% to 65% for suburban commutes).
  3. 3Input your vehicle’s official EPA City and Highway MPG ratings.
  4. 4Enter your average local fuel price per gallon.

Assumptions & Limitations

  • Assumes driving behavior aligns with standardized EPA dyno testing cycles.

Frequently Asked Questions

Why can’t I just average my city and highway MPG?

Averaging MPG directly (arithmetic mean) is mathematically flawed because MPG is a rate of distance per volume. Gallons consumed depends on the inverse (gallons per mile). The harmonic mean accurately weights the extra gas consumed in stop-and-go city traffic.

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