How it works
Monthly cash flow follows the movement of money through rental operations and financing. It shows the amount remaining after a vacancy allowance, routine costs, loan payments and any entered capital reserve.
The formula
Keep currency, units and time periods consistent. Percentage inputs use percentage points (enter 5 for 5%). Results are rounded only for display; tiny nonzero values may use scientific notation. Undefined ratios are shown as unavailable.
$2,800 rent plus $100 other income, an explicit $140 vacancy loss, $650 operating costs and $1,450 mortgage payment leave $660/month or $7,920/year. NOI is $2,110/month before financing.
Calculation method
NOI appears separately so a financing payment does not look like an operating expense. Fixed dollar vacancy loss and percentage vacancy use different break-even equations; the tool preserves the selected assumption.
Interpretation
A negative result is the exact modeled monthly shortfall. A replacement reserve is a planning deduction below NOI, not a claim that the same amount will be spent every month.
Limitations
All rents, values, vacancy, expenses and financing terms are your assumptions. Figures exclude income tax and appreciation. Inputs stay in your browser. These calculations do not predict loan approval or investment outcomes.
Method and reference sources
Method and content checked 2026-09-20. These sources provide background, not endorsement or professional certification. The formula and limitations above define this calculator.
- CFPB — How lenders calculate mortgage paymentsLoan principal-and-interest context; property operating expenses and underwriting assumptions are separate.
Frequently asked questions
Why should I include a vacancy allowance?
Scheduled rent may not all be collected. An allowance reduces modeled income, but it does not forecast specific vacancies or cover all unusual repairs and capital expenses.
What is a worked example for Monthly Cash Flow?
$2,800 rent plus $100 other income, an explicit $140 vacancy loss, $650 operating costs and $1,450 mortgage payment leave $660/month or $7,920/year. NOI is $2,110/month before financing.