The rule of thumb
The single biggest factor is utilization. Use a personnel / mast lift more than ~12–14 days a month and buying usually wins; below that, renting is cheaper once you count maintenance, insurance, storage, and depreciation.
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. If your personnel / mast lift usage is seasonal or project-driven, a rental-first approach keeps capital free.