Gas vs. Diesel Cost Comparison Calculator
Quick answer: Diesel usually wins only when its MPG advantage and fuel savings overcome the higher upfront and maintenance costs. Use your own numbers below — every input updates the URL so you can share or save the scenario.
Your inputs
Numbers update results and the URL instantly.
mi/yr
mpg
mpg
$/gal
$/gal
¢/gal
¢/gal
Ownership economics
$
$
yr
$
Annual fuel cost
Gas
$1,875
Diesel
$1,671
Annual difference
Diesel saves $204
Over 5 years
$1,018 saved
Break-even analysis
How long, or how many miles, until diesel's fuel savings cover its upfront and maintenance premium (minus resale).
Net diesel premium
$3,500
upfront + maintenance − resale
Break-even years
17.2 yr
Break-even annual miles
51,579 mi/yr
within 5 years
Gas remains cheaper
Gas wins on fuel cost only if you don't keep the diesel long enough — at these inputs, diesel's fuel savings never recoup the upfront and maintenance premium inside your ownership window.
Price spread sensitivity
Annual fuel difference and break-even if the diesel-vs-gas price spread changes from today's $0.40/gal.
| Diesel − gas | Annual difference | Break-even years |
|---|---|---|
| -$0.50/gal | Diesel saves $589 | 5.9 yr |
| -$0.25/gal | Diesel saves $482 | 7.3 yr |
| +$0.00/gal | Diesel saves $375 | 9.3 yr |
| +$0.25/gal | Diesel saves $268 | 13.1 yr |
| +$0.50/gal | Diesel saves $161 | 21.8 yr |
| +$0.75/gal | Diesel saves $54 | 65.3 yr |
| +$1.00/gal | Gas saves $54 | — |
Keep reading
Background and related tools to pressure-test the result.
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Frequently asked questions
- Is diesel always cheaper than gas?
- No. Diesel pump prices are often higher than regular gas, but diesel engines typically deliver 20–35% better MPG. Diesel wins on running cost only when its MPG advantage and any fuel-card discount cover the price gap. The upfront premium and maintenance costs determine whether it wins overall.
- How do I calculate diesel break-even?
- Divide the net diesel premium — upfront price difference plus expected lifetime maintenance difference minus expected resale advantage — by the annual fuel savings from better MPG. The result is the number of years you need to keep the vehicle for diesel to pay back.
- Should fleets compare gas and diesel differently?
- Yes. Fleets should weight high annual mileage, duty cycle, idling, fuel-card pricing, and resale at predictable replacement intervals. At 50,000+ miles per year, diesel's per-mile fuel advantage compounds quickly and usually clears the premium long before resale.