Separate maintenance, repairs and downtime
Routine maintenance is planned service. Repairs address diagnosed faults or an explicit contingency. Downtime is the cost of being unable to use the truck. Keep the three categories separate so an optimistic maintenance allowance does not conceal unresolved repairs or business interruption.
Use local written quotes for known work. For downtime, estimate the number of unavailable days and a daily net cost you can explain. A rental charge and lost business contribution may overlap, so do not automatically add both at their maximum values. Count only costs that apply to the scenario you are modelling.
Read cost per kilometre as a cash-budget result
The calculator adds annual payments, fuel, maintenance, repair allowance, insurance, registration and the entered downtime scenario. Dividing that annual total by your annual kilometres gives a cash-budget cost per kilometre. A low annual distance spreads fixed costs over fewer kilometres; it does not mean the truck itself has become less mechanically efficient.
This is not a full economic ownership or tax calculation. Loan principal is part of cash payments, while depreciation is a separate economic concept; adding both without a consistent model can double-count part of the purchase cost. Taxes, resale proceeds and business-use treatment require their own assessment. Use the same method when comparing two trucks.
Stress-test the uncertain parts of the budget
Run a base case using known quotes, then change fuel use, repair allowance and downtime individually. Note which assumption changes the buying decision. If the result depends on an unknown major fault being inexpensive, arrange diagnosis rather than treating the calculator as evidence that the purchase is affordable.
For a commercial truck, check that a proposed replacement can carry the required crew, cargo and trailer. An available vehicle that cannot perform the job does not provide full operational coverage.