How do I calculate cash flow, cap rate, and return on investment for a rental property?

Investors throw around cash flow, cap rate, and ROI as if they were winning lottery numbers, but each one is just a small piece of arithmetic. Learned in the right order, they turn a rental from a leap of faith into a spreadsheet you can trust. The trick is not the math, which is easy; it is the honesty of the inputs, which is hard.

Cash flow, in plain words

Cash flow answers one question: after every bill is paid, does this rental put money in your pocket each month? The formula is simple: monthly rent minus the mortgage payment minus property taxes, insurance, management, maintenance, vacancy reserve, and HOA dues. Positive cash flow means the property contributes; negative means it costs you monthly, and you should know that before you buy, not after.

Cap rate for comparing deals

Cap rate is net operating income, income minus operating expenses with no mortgage, divided by the property's value. Expressed as a percentage, it lets you compare a duplex in Sacramento against an apartment in Roseville on the same scale, regardless of how each buyer finances it. Higher cap rates generally mean more income relative to price, but they often come with older buildings, lower-end tenants, or more maintenance, so the cap rate is a comparison tool, not a verdict.

ROI and cash-on-cash

Return on investment measures what the property earns against what you actually put in. The most practical version for rental buyers is cash-on-cash: annual cash flow divided by your total cash invested, down payment plus closing costs. If you put $80,000 in and the property returns $8,000 a year in cash flow, that is a 10 percent cash-on-cash return before appreciation and tax benefits. It is the number that tells you whether your money is working.

The expenses everyone forgets

The difference between a pro-forma that cash flows and a real property that does not is usually the missing line items: vacancy between tenants, turnover paint and cleaning, big-ticket maintenance like roofs and HVAC, property management at 8 to 10 percent of rent, insurance, and periodic capital reserves. Sacramento and the surrounding counties each have their own property tax and insurance realities, so use local numbers, not national averages.

Put the numbers to work

Run the analysis three times: optimistic, realistic, and pessimistic, and buy only if the realistic column works. That discipline alone separates the investors who build portfolios from the ones who fund other people's. Our starting an investment portfolio guide walks the full evaluation, and investment performance shows how to review what you already own.