Most cash-flow math is wrong in the same direction: optimistic. It subtracts the mortgage, taxes, and insurance from rent, calls the difference “cash flow,” and ignores the costs that don't show up every month but absolutely show up over time. A property that looks like it nets $500 a month on paper can net half that — or nothing — once you reserve honestly.
The last four are reserves. Leaving them out is the most common way investors overstate a deal.
The fixed costs (entered as dollars)
- Mortgage (P&I) — enter your payment directly, or let the calculator estimate it from loan amount, rate, and term.
- Property taxes — verify the actual figure for the parcel; NJ rates swing widely by town and a wrong number moves cash flow by hundreds a month.
- Insurance — landlord/hazard, plus flood where required.
- HOA — condo or association dues, if any.
The reserves (entered as a % of rent)
Vacancy, maintenance, management, and CapEx scale with rent, not with a fixed dollar figure, so they're entered as percentages. Common starting points are 5% vacancy, 5% maintenance, 8% management, and 5% CapEx — adjust them to your market and the property's condition. Even if you self-manage and nothing is broken today, reserve for all four: management is real labor, and roofs, HVAC, and water heaters fail on a schedule. To bring the loan's own coverage test into view, pair this with the DSCR calculator; to compare the unlevered yield across deals, use the cap rate calculator.
Cash-on-cash return
Enter your total cash invested — down payment plus closing costs plus rehab — and the calculator returns your cash-on-cash return: annual cash flow divided by the money you actually committed. It's the yield on your cash, separate from appreciation or loan paydown, and it's how you compare a rental against any other place you could have put that capital.