Cash-on-cash: the return on the cash you actually risked
Cash-on-cash return measures a rental property's annual cash flow — rent minus every operating cost and minus the mortgage payment — against the total cash you personally put into the deal: the down payment plus closing and rehab costs. If a property puts $4,000 a year in your pocket after every bill and you invested $80,000 of your own money to buy it, the cash-on-cash return is 5%. It is the rental world's version of asking "what is my money earning?" rather than "what is the property earning?"
The difference between this and the cap rate is leverage. Cap rate ignores the loan entirely, so it never changes with your down payment or interest rate. Cash-on-cash is built on the loan: a smaller down payment can push it sharply higher when things go well, because the same cash flow is divided by less invested cash — and can push it negative just as fast when rent dips or a roof fails, because the mortgage payment does not shrink with your luck. Neither number is "the true one." Cap rate grades the property; cash-on-cash grades the deal structure.
This calculator labels the result the way the full Vickery Finance analyzer does: 8% or better is Strong, 4% to 8% is Workable, and under 4% is Thin — labels, not promises. A thin return is not automatically a bad purchase (appreciation, loan paydown and tax treatment also matter, and none of them appear here), but it does mean the deal has little cushion. Before you buy, stress-test it: raise the vacancy and maintenance percentages, drop the rent slightly, and see whether the return you are counting on survives ordinary bad luck.