The rule of thumb
The single biggest factor is utilization. Use a generator more than ~12–14 days a month and buying usually wins; below that, renting is cheaper once you count maintenance, insurance, storage, and depreciation. At $80–$600 a day, a month of rental runs about $680–$5,700, which is the figure to hold the ownership cost against. The rental guide prices 5 classes, from portable <10kW at $70–$90 a day to 250kW+ at $528–$630.
What to include in the math
Purchase price and financing, maintenance and parts, insurance, storage and transport, operator training — and, crucially, depreciation and resale value. The calculator above bundles these into a monthly figure so you can compare like-for-like.
Rent, buy, or both?
Many contractors own the machines they use constantly and rent for peaks and specialty jobs. A generator earns its keep on temporary power, events, backup power, remote sites; if that work is seasonal or project-driven, a rental-first approach keeps capital free.