 Costs are not the same each month. If 9,600 miles are driven one month and 10,000 miles the next, two different sets of costs apply for each month. For example, if your tractor payment is $1,850 per month and you drive 9,600 miles in the month, your tractor payment is costing you 19.3 cents per mile. Drive 10,000 miles, though, and that same payment will cost you 18.5 cents per mile. This is one of your major fixed costs while paying off a truck loan. The difference in this example is only a fraction of a cent.