Separate road fuel from idle fuel
Road gallons are trip miles divided by expected MPG. Idle gallons are idle hours multiplied by the burn rate entered. CDLMath adds those gallons, applies the diesel price, then adds tolls and other expenses to show total trip cost and cost per mile.
Use an MPG that fits the load and route. Weight, hills, headwinds, speed, winter weather, traffic, and equipment all change fuel economy. Idle consumption also varies with engine, accessories, ambient conditions, idle speed, and whether an APU or battery system is doing the work.
Example
A 600-mile trip at 7.5 MPG uses 80 road gallons. Two hours of idle at 0.8 gallon per hour adds 1.6 gallons. At $3.75 per gallon, fuel costs $306. Add $28 in tolls and $15 in other costs for a $349 trip estimate, or about 58 cents per mile.
The default 0.8-gallon idle rate is an adjustable planning example found in a U.S. Department of Energy methodology. It is not a claim about every current truck. Replace it with a measured rate when you have one.
This is not a complete operating-cost or profit calculator. Payments, maintenance, tires, insurance, depreciation, taxes, labor, and overhead are outside the result unless deliberately entered under other costs.