MPG Comparison Calculator

MPG comparison between two vehicles calculates the real annual fuel cost difference, helping buyers and drivers make data-driven decisions about fuel economy.

The core formulas:

Annual Fuel Cost = (Annual Miles / MPG) × Price per Gallon

Annual Savings = Annual Cost (Vehicle A) − Annual Cost (Vehicle B)

Payback Period = Price Difference / Annual Savings

5-Year Fuel Cost = Annual Fuel Cost × 5

What each variable means:

• Annual Miles: how far you drive per year (US average: 12,000–15,000 miles)
• MPG: miles per gallon for each vehicle under your typical driving conditions
• Price per Gallon: current local fuel price; use a 5-year average for long-term comparisons
• Payback Period: how long the fuel savings take to offset a higher purchase price

Worked example: Vehicle A: 28 MPG, priced at $28,000. Vehicle B: 42 MPG, priced at $34,000. Annual miles: 14,000. Gas price: $3.50/gallon.

Annual cost A = (14,000 / 28) × $3.50 = 500 × $3.50 = $1,750/year Annual cost B = (14,000 / 42) × $3.50 = 333.3 × $3.50 = $1,167/year Annual savings = $1,750 − $1,167 = $583/year Price difference = $34,000 − $28,000 = $6,000 Payback period = $6,000 / $583 = 10.3 years

Key insight: The payback period exceeds the typical 7 to 8 year ownership period in this example. At $4.50 gas, or 20,000 miles a year, payback drops under 5 years. Run the numbers for your own situation rather than trusting the rule of thumb, because the answer swings hard on both inputs.

EPA (Environmental Protection Agency) ratings are tested under ideal conditions. Real-world MPG is typically 15–25% lower, and the gap is widest on the hybrids, which do their best work in exactly the stop-and-go city driving the test cycle under-represents.

Fuel is not the whole comparison. The break-even figure below covers fuel only. Insurance, tires, and the resale value three years out can all move more money than the pump does, and a hybrid battery out of warranty is the one repair bill with no equivalent on the gas side. Treat the payback number as one line in the decision, not the decision.