A property’s cost basis is most affected by an owner’s:

Debt service refers to mortgage principal and interest payments, which represent financing costs rather than investment in the property itself; paying down a loan does not increase what the property is worth as an asset or change the owner's tax basis.

Interest expense on a mortgage is a deductible operating expense in the year it is paid, not a capital expenditure, so it reduces taxable income annually but does not increase the property's cost basis.

Costs of operation — such as property management fees, utilities, landscaping, and routine repairs — are expensed in the year incurred as ordinary business deductions and do not represent permanent improvements to the asset, so they do not affect cost basis.