Rental Cash Flow
Calculator

Net operating income (NOI) is rental income minus operating expenses, before financing. Cash flow goes one step further by also subtracting the mortgage payment (principal and interest), giving you the actual cash left in your pocket each month after every expense, including debt service.

A property can have strong NOI and appreciation potential while still producing negative monthly cash flow if the mortgage payment is large relative to rental income — common with high leverage or a low-rent, high-price market. Negative cash flow means you're subsidizing the property from other income each month.

A common conservative default is 5% to 8% of gross rent for stable markets, though this should be adjusted based on your specific area's typical tenant turnover and local rental demand. Using 0% vacancy will overstate cash flow and hide realistic risk.

Most cash flow calculators only reflect current, known operating expenses unless you separately budget a capital expenditure (CapEx) reserve — a monthly set-aside for future big-ticket repairs like a roof or HVAC replacement. Skipping this reserve makes cash flow look better than it will be over time.

Not by itself — positive cash flow confirms the property covers its bills, but a full evaluation should also weigh appreciation potential, cap rate relative to the market, and total return including principal paydown. Cash flow is one important piece of the picture, not the whole picture.