Two properties, both listed at 240,000 dollars, both collecting 28,800 dollars a year in rent. Identical gross rent multiplier of 8.33 on each.
One of them has a cap rate of 6.28 percent. The other has a cap rate of 3.69 percent.
That gap is the entire reason this comparison matters. The gross rent multiplier and the cap rate look like alternative versions of the same idea, and investors use them interchangeably as if picking one were a matter of taste. They are not interchangeable. One of them cannot see expenses at all, and on properties where expenses differ, that blindness is the difference between a solid buy and a slow bleed.
What each one is
Gross rent multiplier is purchase price divided by annual gross scheduled rent. A property at 240,000 collecting 28,800 has a GRM of 8.33. It is a payback style figure: at this rent, ignoring every cost, the property returns its price in 8.33 years.
Cap rate is net operating income divided by purchase price. Net operating income is rent after vacancy and after every operating expense, but before debt service. A property producing 15,071 on a 240,000 price has a cap rate of 6.28 percent.
The single structural difference: GRM uses the top line and cap rate uses the line after costs. Everything else follows from that.
GRM is fast, uses only public information, and needs nothing from the seller. You can compute it from a listing in five seconds. Cap rate requires an expense picture, which means either a real operating statement or a set of assumptions you build yourself, and building net operating income properly is where most of the work sits.
The two properties
Both at 240,000 dollars, both collecting 2,400 a month, both with 5 percent vacancy giving effective gross income of 27,360 dollars.
Property A: a 1990s duplex, tenants pay their own utilities.
- Operating expenses: 12,289 dollars
- Net operating income: 15,071 dollars
- GRM 8.33, cap rate 6.28 percent
Property B: a century duplex, master metered water and heat, heavy deferred maintenance.
- Operating expenses: 18,500 dollars
- Net operating income: 8,860 dollars
- GRM 8.33, cap rate 3.69 percent
The GRM says these are the same deal. The cap rate says one produces 70 percent more income than the other. The cap rate is right, and the reason is entirely contained in the six thousand dollar expense gap: owner paid utilities, older systems, and a maintenance load that reflects the age of the building. That is exactly the spread that an operating expense ratio is built to surface.
Now run it the other way, because cap rate has its own blind spots.
Property C: price 300,000, gross rent 30,000, expenses and vacancy of 11,100, net operating income 18,900. Cap rate 6.30 percent, GRM 10.0.
Property D: price 200,000, gross rent 28,000, expenses and vacancy of 15,400, net operating income 12,600. Cap rate 6.30 percent, GRM 7.14.
Identical cap rates. GRMs that differ by 40 percent. D collects far more rent per dollar of price and gives most of it back in operating costs. C collects less rent per dollar and keeps more of it.
Those are genuinely different assets with different risk profiles. D has more revenue running through it, which means more exposure to a maintenance surprise but also more room to improve the ratio through operations. C is closer to a finished product. The cap rate treats them as twins. It cannot see the difference because it has already netted the expenses away.
The formula that connects them
The two metrics are not independent. They are related exactly, and the relationship is worth committing to memory:
Cap rate = (1 minus the total expense load) divided by GRM
Where the total expense load is operating expenses plus vacancy, expressed as a share of gross scheduled rent.
Check it on Property A. Expenses of 12,289 plus vacancy of 1,440 is 13,729, which against 28,800 of gross scheduled rent is an expense load of 47.67 percent. So the calculation is one minus 0.4767, divided by 8.33.
0.5233 divided by 8.33 equals 6.28 percent. Exactly the cap rate.
This identity does three useful things.
It shows GRM is a cap rate with the expense term deleted. Not a different concept. The same concept, missing one input. That reframes the whole comparison: GRM is not a worse metric, it is an incomplete one, and it is incomplete in a completely predictable way.
It lets you back into an implied expense load. If a broker gives you a cap rate and you can compute the GRM from the price and the rent roll, you can solve for the expense assumption the broker used. Do this. When a 7.5 cap on a 9.0 GRM implies an expense load of 32.5 percent on a hundred year old building with master metered water, you have found the place where the marketing package is doing its work, and you have found it in about forty seconds.
It gives you a fair GRM target for your own market. Decide the cap rate you need and the expense load you actually expect. If you want a 7 percent cap and you honestly expect a 45 percent load, your maximum GRM is 0.55 divided by 0.07, or 7.86. Now you have a screening number you can apply to a listing sheet without opening a spreadsheet, and it is calibrated to your return requirement rather than borrowed from someone else’s market.
When to use each one
Use GRM when you are screening. Twenty listings, no operating statements, an hour on a Saturday. GRM is the correct tool. It requires nothing you do not already have and it will correctly rank properties within a homogeneous set. If you are looking at eight similar vinyl sided duplexes in the same submarket with the same utility arrangement, the expense loads really are close to identical, and in that narrow case GRM and cap rate will rank the properties in the same order. What GRM shows and what it hides is worth reading before you lean on it hard.
Use cap rate when you are underwriting. One property, real numbers, an actual decision. At that point the expense load stops being an assumption and becomes something you should know, and cap rate is the only one of the two that reflects it. Cap rate against the coverage ratio covers the other comparison worth understanding at that stage, because the number a lender computes is not the number you compute.
Never compare GRM across dissimilar properties. A GRM of 8 on a modern townhouse with tenant paid everything and a GRM of 8 on a pre-war building with a boiler are not comparable numbers and treating them as such is the specific mistake this article exists to prevent.
Never accept a cap rate without seeing the expense schedule. A cap rate is a claim about expenses wearing the costume of a fact. Ask what maintenance was assumed, whether management was included at market rate or excluded because the seller self managed, and whether any capital items got quietly categorized as repairs. Excluding management alone will move a cap rate by half a point or more on a small residential deal.
What both of them miss
Both metrics deliberately ignore financing. That is a feature, since it lets you compare properties rather than loans, but it means neither one tells you whether you can actually buy the thing.
Loan proceeds are constrained by coverage, not by cap rate, and the conversion between the two runs through the loan constant. If the constant is above your cap rate you have negative leverage, and a property with a lovely 6.3 cap can still turn into a half percent cash-on-cash return once the loan is on it. The DSCR deal calculator is the fastest way to see what a given price and rent will actually support, and the coverage ratio walk through explains why the lender’s arithmetic differs from yours.
Both also ignore capital replacement entirely. A cap rate computed on a building with a twenty five year old roof and a cap rate computed on the same building with a new one are the same number, right up until the roof fails. Capital reserves live outside both metrics, and on older properties that omission is larger than the difference between the two metrics you are comparing.
And both are single year snapshots. Neither says anything about rent growth, principal paydown, or what happens at the exit, which is what IRR and equity multiple are for.
One more boundary worth naming: neither metric applies to a renovation and resale. If you are buying to improve and sell rather than to hold and rent, the governing arithmetic is the spread between your all in cost and the resale value, which is the seventy percent rule and the profit margin question, not a yield calculation. The financing is different too, and holding that kind of project inside an entity brings its own requirements, which financing flips through an entity covers.
The practical routine
Screen on GRM. Compute it on everything, rank the list, and throw out the top third without further thought.
On what survives, estimate an expense load and use the identity to convert your GRM into an implied cap rate. That takes one division and it will kill most of the remaining candidates before you have requested a single document.
On the handful left, build a real expense schedule and compute an actual cap rate. Compare your number to the one in the marketing package and look hard at the difference, because the difference is the negotiation.
Then check the leverage. Cap rate against the loan constant tells you whether borrowing helps. Break-even occupancy tells you how much can go wrong before it stops working. And the 1 percent rule is a reasonable last sanity check on whether the rent is plausible for the price in the first place.
Two metrics, one formula between them, and a rule that covers nearly every case: gross rent multiplier for speed, cap rate for truth, and never compare either one across buildings that do not cost the same to operate.
We are a Pittsburgh-based brokerage and we finance investment properties for investors across Pennsylvania and additional states. If you have a listing and you want to know what it will actually support in financing before you write the offer, send it through our contact page or call 412-990-2941.
FMC Capital, NMLS #1840537. This article is general information for real estate investors and is not a commitment to lend or an offer of specific terms. All figures shown are illustrative. Rates, expense assumptions, coverage thresholds, and program guidelines vary by lender, property, and borrower and are subject to change.
Licensed mortgage broker, NMLS #1840537. Loan products and qualification standards vary and are subject to change without notice.