Cap Rate & GRM Calculator

Two metrics that disagree usefully

Cap rate is net operating income divided by price. It accounts for every operating expense, so it reflects how the property actually performs. GRM is price divided by annual gross rent, and it ignores expenses completely.

That sounds like a reason to only use cap rate, but the gap between the two is itself the information. Two properties can carry identical GRMs and very different cap rates, and the entire difference is expense structure — one has a higher tax bill, owner-paid utilities, or a management fee the other doesn’t. GRM is the metric you can compute from a listing you don’t trust; cap rate is the one you compute after the seller sends actual statements. When the two rank a pair of properties differently, the expenses are what to dig into.

Why NOI excludes your mortgage

Net operating income deliberately leaves out all debt service. It looks like an omission and it’s actually the point: financing is a fact about you — your down payment, your rate, your term — not about the building. Two investors bidding on the same property compute the same NOI and the same cap rate, then end up with very different cash flow depending on how they borrow.

That’s what makes cap rate a property-comparison metric rather than a deal-comparison metric. If you want the leveraged figure that includes your mortgage payment, you want cash-on-cash return, which divides actual cash flow by the cash you put in. NOI also excludes capital improvements, which are depreciated rather than expensed — the rental bookkeeping guide covers where that line falls.

Valuing income at a market cap rate

Run the cap rate formula backwards and it becomes a valuation tool: value = NOI ÷ market cap rate. Feed it the cap rate comparable sales are actually trading at and you get what this property’s income is worth at market pricing, independent of what the seller is asking. A property producing $18,500 of NOI is worth about $264,000 in a 7%-cap submarket and about $370,000 in a 5%-cap one — the same income, priced by two different markets.

The calculator runs the same exercise with a market GRM, giving you a second, expense-blind opinion on the same question. It also inverts the formula the other direction: given the return you require, it reports the maximum price at which this income still clears your hurdle. That number is your walk-away price.

A high cap rate is compensation, not a bargain

Cap rate cannot be scored in isolation, and treating a big number as an automatic win is the most expensive mistake this metric invites. A 4% cap in a prime coastal market and a 12% cap in a declining tertiary market can both be correctly priced. The low one buys stability, strong tenant demand, and expected appreciation. The high one pays you for vacancy risk, aging building systems, a thinner tenant pool, and management intensity.

So a cap rate well above local comparable sales is a question, not a discount. Ask what the market knows about that property or that street that you don’t. Two of the most common answers: the pro-forma rent is above what the units actually achieve, and the property tax line reflects the seller’s decades-old assessed basis rather than the reassessment that follows your purchase.

Sanity-check the expense ratio

Operating expenses on residential rentals typically land between 35% and 50% of effective gross income once every line is counted. When a listing pro-forma shows 15% or 20%, something is missing — most often property management, a maintenance and capital-expenditure reserve, or the real tax bill after reassessment. An understated expense ratio inflates NOI, which inflates the cap rate, which makes an ordinary deal look excellent. The calculator flags ratios that fall outside the plausible band so an optimistic pro-forma doesn’t pass quietly.

Frequently asked questions