Rental Property Calculator – Cash Flow, Cap Rate and Cash-on-Cash, Honestly

Three levers that turn a loser into a payer

Every figure below was run through the calculator above, starting from its default deal — a $300,000 property, 20% down, a $240,000 loan at 6.5% over 30 years, $2,200 a month of rent, vacancy 5%, tax $3,600, insurance $1,200, maintenance 5% and management 8% — and changing one thing at a time. The default deal loses money: net operating income of $16,848 a year against debt service of $18,203.52, cash flow of −$1,355.52 a year or −$112.96 a month, a cap rate of 5.62% and a cash-on-cash return of −2.26%. A positive cap rate with negative cash flow is the most common landlord surprise, and the three levers below show which fixes actually fix it.

The rent lever is the most powerful one on this deal, because rent flows through every downstream number. Raising the rent from $2,200 to $2,600 a month — $400 more, or $4,800 more a year at full occupancy — lifts net operating income from $16,848 to $20,784, the cap rate from 5.62% to 6.93%, and monthly cash flow from −$112.96 to +$215.04, with cash-on-cash swinging from −2.26% to 4.30% and the debt coverage ratio from 0.93 to 1.14. Note what did not change: the mortgage payment stayed exactly $1,516.96, because the loan was untouched. Every dollar of extra rent, after vacancy and the percentage-based costs, lands in cash flow — which is why rent is the lever landlords reach for first, and also why it is the lever most constrained by reality: the market, not the calculator, decides whether $2,600 is achievable for this property.

The down payment lever fixes the deal without touching the property at all. Raising the down payment from 20% to 40% cuts the loan from $240,000 to $180,000 and the monthly mortgage payment from $1,516.96 to $1,137.72, so monthly cash flow becomes +$266.28 and cash-on-cash 2.66%, with debt service falling to $13,652.64 a year and DSCR rising to 1.23. But the cap rate does not move — it stays exactly 5.62%, because the cap rate divides NOI by price and neither changed. That immobility is the lesson: the cap rate measures the property, and the down payment measures the financing. A deal can have a mediocre cap rate and a healthy cash flow if it is financed conservatively, or a strong cap rate and a negative cash flow if it is financed aggressively — and the default deal is the second kind. The cash-on-cash return also improves less dramatically than the cash flow itself, because the cash put in doubled from $60,000 to $120,000: the same dollars of cash flow are now divided by twice the cash, so 2.66% on $120,000 is a larger pile of money at a lower percentage return than 4.30% on $60,000 in the rent case.

The vacancy lever is the one that teaches humility. Setting vacancy to 0% — assuming the property is never empty, which no real property achieves — lifts NOI to $18,168 and the cap rate to 6.06%, yet monthly cash flow is still −$2.96, with cash-on-cash at −0.06% and annual cash flow at −$35.52. Even perfect occupancy does not save this deal, because the gap was never really about vacancy: it was about a $1,516.96 mortgage payment against $1,404.00 a month of NOI. The page’s own warning belongs here verbatim in spirit: a calculator that lets you invent a zero vacancy is not helping you, it is flattering you — and on this deal even the flattering zero is not enough. When a lever cannot fix the deal even at its most optimistic setting, the deal’s problem lies elsewhere, and the elsewhere here is the loan.

For contrast, the page’s own smaller deal shows the same formula producing the opposite verdict: a $180,000 property at $1,650 a month collects $19,800 a year, with $6,864 of outgoings, NOI of $12,936, a cap rate of 7.19%, and with 25% down a loan of $135,000 at 6.5% over 30 years costing $853.29 a month — cash flow of $224.71 a month and cash-on-cash of 5.99% on $45,000 cash put in. Same formula, different price and rent: that is the whole game. And the cash-purchase identity is the check that keeps every other calculation honest: with no loan, cash flow is the whole NOI of $16,848, and $16,848 on $300,000 of cash is 5.62% — cash-on-cash exactly equal to cap rate. If any tool shows a different cash-on-cash than cap rate on a cash deal, its arithmetic, not the market, is wrong.

Cap rate, cash-on-cash, and DSCR: three lenses, one property

Three ratios sit on this page, and confusing them is how losing deals get bought. The cap rate is NOI divided by price: $16,848 ÷ $300,000 = 5.62% on the default deal. It ignores the loan entirely, which is both its strength and its blindness — strength, because it lets you compare properties regardless of how they are financed; blindness, because no landlord actually receives the cap rate unless they paid cash. The cash-on-cash return is cash flow divided by cash put in: −$1,355.52 ÷ $60,000 = −2.26% on the default deal. It includes the loan, so it is the return on the money you actually committed — but it moves when the financing moves even if the property does not, as the 40%-down case proves (same property, same cap rate, cash-on-cash now +2.66%). Neither ratio is “the” return; they answer different questions, and a deal should be judged on both.

The debt service coverage ratio, DSCR, is NOI divided by annual debt service, and it answers the lender’s question: does the property’s own earnings cover its loan payments? On the default deal, $16,848 ÷ $18,203.52 = 0.93 — the property’s earnings cover only 93% of the debt service, and the missing 7% comes out of the owner’s pocket, which is exactly the −$112.96 a month the cash flow shows. After the rent rise to $2,600, DSCR is 1.14: earnings cover the debt service with 14% to spare. After the 40% down payment, DSCR is 1.23. A DSCR below 1.00 is the arithmetic definition of a property that does not pay for itself; a DSCR comfortably above 1.00 is the cushion that lets a property survive a vacancy, a repair bill, or a rate rise without calling on the owner. Lenders watch DSCR for the same reason owners should: it is the earliest warning that the loan, not the property, is the problem.

Two habits follow. First, never underwrite a deal on cap rate alone, and never on cash-on-cash alone: the first hides the loan, the second hides the property. A 5.62% cap rate with a 6.5% mortgage rate, as in the default deal, is a property that does not pay for itself whatever the market average says — because the loan costs more, per dollar, than the property earns per dollar, and leverage then works against you instead of for you. Second, price every cost line honestly before believing any ratio: vacancy is not a missing month you hope away but a cost line at the percentage you type in, maintenance and management are percentages of rent that rise when rent rises, and tax and insurance are fixed bills that do not fall when rent does. The page’s breakdown — every cost line, one by one, with its share of rent — exists so that a flattering ratio can be traced back to the line that flattered it. A ratio built on invented zeros is not an analysis; it is a wish with decimal places.

One sentence to carry away from this page: the property earns the cap rate, the loan eats the debt service, and you keep what is left. On the default deal the property earns $16,848, the loan eats $18,203.52, and you keep −$1,355.52 a year. Every improvement to the deal must move one of those three numbers — more rent or lower costs to raise the earnings, a smaller loan or a lower rate to cut the eating, or more cash in to change what the remainder means as a percentage. A pitch that improves none of the three, however glossy its ratio, improves nothing at all.