Diesel vs Gas Car: 5-Year Total Cost Comparison Tool

What does gas winning by $5,973.21 mean?

It means the gas car costs $5,973.21 less than the diesel over 5 years — $39,714.29 against $45,687.50. The diesel burns less fuel but costs $6,000.00 more to buy, and the fuel saving is only $5.36 a year: $1,537.50 a year for the diesel against $1,542.86 for the gas car. The diesel fuel costs more per gallon, so the diesel’s better mpg barely shows up in the fuel bill. The difference is the diesel total minus the gas total — a positive difference means gas wins, a negative one means diesel wins — and the verdict is the same number in words.

Three things to check before you trust the number

The purchase price is the whole story on the defaults. The fuel saving is $5.36 a year, so the $6,000.00 premium takes 1,120.00 years to pay back. If the diesel cost the same as the gas car, the diesel would win by $26.79 on fuel alone — the premium, not the fuel, is why the gas car wins.

The mpg gap has to be enormous to matter. The diesel would have to do 143.51 mpg to win at the default prices, or the gas car would have to fall to 15.79 mpg. At 50 mpg against a 20 mpg gas car the gap is only $120.00. A few mpg either way moves the answer by hundreds, not thousands.

The miles have to be absurd to flip it. You would have to drive 2,688,001 miles a year for the diesel to win — more miles in a year than any car can do. At 100,000 miles a year the diesel still loses by $5,776.79. If your driving is normal, the purchase price decides.

Worked example

On the defaults: diesel $38,000.00 at 32 mpg and $4.10 a gallon; gas $32,000.00 at 28 mpg and $3.60 a gallon; 12,000 miles a year; 5 years.

1. Diesel fuel per year: 12,000 ÷ 32 × $4.10 = $1,537.50.
2. Gas fuel per year: 12,000 ÷ 28 × $3.60 = $1,542.86.
3. Diesel total: $38,000.00 + 5 × $1,537.50 = $45,687.50.
4. Gas total: $32,000.00 + 5 × $1,542.86 = $39,714.29.
5. Difference: $45,687.50 − $39,714.29 = $5,973.21 — gas wins.
6. Payback: $6,000.00 ÷ $5.36 a year = 1,120.00 years.
7. Largest diesel price for diesel to still win: $32,026 — at $32,026 the diesel wins by $0.79, and at $32,027 the gas car wins by $0.21.

Every branch, checked

• 25,000 miles a year: 25,000 miles a year: Diesel $54,015.63; gas $48,071.43 — Gas wins by $5,944.20. More miles means more fuel, and the diesel saves only a little per mile — the gap barely moves.
• 6,000 miles a year: 6,000 miles a year: Diesel $41,843.75; gas $35,857.14 — Gas wins by $5,986.61. Fewer miles means less fuel, so the purchase-price gap dominates even more.
• 10 years: 10 years: Diesel $53,375.00; gas $47,428.57 — Gas wins by $5,946.43. Ten years of fuel, and the diesel still does not catch up — the $6,000 premium is too big for the fuel saving.
• 3 years: 3 years: Diesel $42,612.50; gas $36,628.57 — Gas wins by $5,983.93. Three years, and the gap is almost the whole premium.
• Diesel 36 mpg: Diesel 36 mpg: Diesel $44,833.33; gas $39,714.29 — Gas wins by $5,119.05. A more efficient diesel saves more fuel, and the gap shrinks by about $854.
• Gas 24 mpg: Gas 24 mpg: Diesel $45,687.50; gas $41,000.00 — Gas wins by $4,687.50. A thirstier gas car burns more fuel, and the gap shrinks by about $1,286.
• Diesel fuel $3.90: Diesel fuel $3.90: Diesel $45,312.50; gas $39,714.29 — Gas wins by $5,598.21. Cheaper diesel fuel helps the diesel, and the gap shrinks by about $375.
• Gas fuel $4.50: Gas fuel $4.50: Diesel $45,687.50; gas $41,642.86 — Gas wins by $4,044.64. Pricier gas fuel hurts the gas car, and the gap shrinks by about $1,929.
• Diesel $34,000: Diesel $34,000: Diesel $41,687.50; gas $39,714.29 — Gas wins by $1,973.21. A $4,000 cheaper diesel cuts the gap by exactly $4,000.
• Gas 32 mpg: Gas 32 mpg: Diesel $45,687.50; gas $38,750.00 — Gas wins by $6,937.50. A more efficient gas car burns less fuel, and the gap grows by about $964.

The reverses, worked backwards

• Largest diesel price for diesel to still win: $32,026 — at $32,026 the figures are Diesel $39,713.50; gas $39,714.29 (unrounded 39714.285714) — Diesel wins by $0.79 (unrounded 0.785714); at the lower neighbor the figures are Diesel $39,712.50; gas $39,714.29 (unrounded 39714.285714) — Diesel wins by $1.79 (unrounded 1.785714); at the upper neighbor the figures are Diesel $39,714.50; gas $39,714.29 (unrounded 39714.285714) — Gas wins by $0.21 (unrounded 0.214286) — verdict: STEP.
• Smallest gas fuel price for diesel to win: $6.39 — at $6.39 the figures are Diesel $45,687.50; gas $45,692.86 (unrounded 45692.857143) — Diesel wins by $5.36 (unrounded 5.357143); at the lower neighbor the figures are Diesel $45,687.50; gas $45,671.43 (unrounded 45671.428571) — Gas wins by $16.07 (unrounded 16.071429); at the upper neighbor the figures are Diesel $45,687.50; gas $45,714.29 (unrounded 45714.285714) — Diesel wins by $26.79 (unrounded 26.785714) — verdict: STEP.
• Smallest diesel mpg for diesel to win: 143.51 mpg — at 143.51 mpg the figures are Diesel $39,714.17 (unrounded 39714.166260); gas $39,714.29 (unrounded 39714.285714) — Diesel wins by $0.12 (unrounded 0.119454); at the lower neighbor the figures are Diesel $39,714.29 (unrounded 39714.285714); gas $39,714.29 (unrounded 39714.285714) — exact tie; at the upper neighbor the figures are Diesel $39,714.05 (unrounded 39714.046823); gas $39,714.29 (unrounded 39714.285714) — Diesel wins by $0.24 (unrounded 0.238892) — verdict: STEP.
• Smallest gas mpg for gas to still win: 15.79 mpg — at 15.79 mpg the figures are Diesel $45,687.50; gas $45,679.54 (unrounded 45679.544015) — Gas wins by $7.96 (unrounded 7.955985); at the lower neighbor the figures are Diesel $45,687.50; gas $45,688.21 (unrounded 45688.212928) — Diesel wins by $0.71 (unrounded 0.712928); at the upper neighbor the figures are Diesel $45,687.50; gas $45,670.89 (unrounded 45670.886076) — Gas wins by $16.61 (unrounded 16.613924) — verdict: STEP.
• Smallest annual miles for diesel to win: 2,688,001 miles a year — at 2,688,001 miles a year the figures are Diesel $1,760,000.64 (unrounded 1760000.640625); gas $1,760,000.64 (unrounded 1760000.642857) — Diesel wins by $0.00 (unrounded 0.002232); at the lower neighbor the figures are Diesel $1,760,000.00; gas $1,760,000.00 — exact tie; at the upper neighbor the figures are Diesel $1,760,001.28 (unrounded 1760001.281250); gas $1,760,001.29 (unrounded 1760001.285714) — Diesel wins by $0.00 (unrounded 0.004464) — verdict: STEP.
• Largest diesel fuel price for diesel to still win: $0.91 — at $0.91 the figures are Diesel $39,706.25; gas $39,714.29 (unrounded 39714.285714) — Diesel wins by $8.04 (unrounded 8.035714); at the lower neighbor the figures are Diesel $39,687.50; gas $39,714.29 (unrounded 39714.285714) — Diesel wins by $26.79 (unrounded 26.785714); at the upper neighbor the figures are Diesel $39,725.00; gas $39,714.29 (unrounded 39714.285714) — Gas wins by $10.71 (unrounded 10.714286) — verdict: STEP.

What the defaults assume

The defaults are one diesel at $38,000, 32 mpg and $4.10 a gallon against one gas car at $32,000, 28 mpg and $3.60 a gallon, driven 12,000 miles a year for 5 years. They are a starting point, not a verdict on diesel: a diesel that costs the same as the gas car wins on fuel alone, and a diesel with a much bigger mpg gap wins by more. Change the eight numbers to the two cars you are actually comparing and the calculator recomputes instantly.

These notes repeat in every explainer section because this page is built to be read start to finish: the defaults are one pair of cars, not a standard; the purchase price is the whole story on the defaults; the mpg gap has to be enormous to matter; and the miles have to be absurd to flip it.

Output · formula · meaning

Who uses this

• A car buyer choosing between a diesel and a gas version of the same car and wanting the whole-period cost, not just the sticker price.
• A high-mileage driver who wonders whether the diesel’s fuel saving ever pays back the premium.
• A fleet manager comparing diesel and gas vans over a five-year replacement cycle.
• A used-car shopper weighing a cheaper gas car against a pricier diesel with better mpg.

Accuracy & limitations

The calculator does the arithmetic exactly — purchase price plus years times miles divided by mpg times fuel price, for each car, then the difference — and every figure on this page is checked against an independent model. What it does not include is everything else a car costs: maintenance, insurance, repairs, depreciation and resale value. A diesel often costs more to maintain and can hold its value differently, and those can move the answer by more than the fuel. Fuel prices also move — the calculator uses the prices you enter, not a forecast — and the mpg is the car’s rated figure, not what you will actually get in traffic.

Cite this calculator

Total cost = purchase price + years × (annual miles ÷ mpg × fuel price per gallon); difference = diesel total − gas total. On the defaults — diesel $38,000.00 at 32 mpg and $4.10 a gallon, gas $32,000.00 at 28 mpg and $3.60 a gallon, 12,000 miles a year, 5 years — the diesel costs $45,687.50 and the gas car costs $39,714.29: gas wins by $5,973.21. Largest diesel price for diesel to still win: $32,026. Smallest gas fuel price for diesel to win: $6.39. Smallest diesel mpg for diesel to win: 143.51 mpg. Smallest gas mpg for gas to still win: 15.79 mpg. Smallest annual miles for diesel to win: 2,688,001. Largest diesel fuel price for diesel to still win: $0.91. Source: Bright Side Kit, brightoolbox.com.

Frequently asked questions