Cap Rate vs Gross Rent Multiplier: Screening Fast Without Getting Fooled

Gross rent multiplier is purchase price divided by annual gross rent. Cap rate is net operating income divided by price. GRM skips the expenses. Cap rate includes them. That is the whole difference, and it decides when each one is safe to use.

A $300,000 house renting for $2,500 a month has a GRM of 10 ($300,000 / $30,000). Its cap rate, after vacancy and $10,230 of operating expenses, is 6.1%.

The formulas

Gross rent multiplier = price / annual gross scheduled rent

Cap rate = net operating income / price

GRM is a multiple, so lower means cheaper. Cap rate is a yield, so higher means cheaper. A property gets more attractive to a buyer as GRM falls and cap rate rises.

How they relate

Since NOI is gross rent minus vacancy minus expenses, the two are linked by the expense ratio:

Cap rate ≈ (1 − vacancy %) × (1 − expense ratio) / GRM

With 5% vacancy and a 36% expense ratio, the numerator is about 0.61. So:

GRM	Monthly rent as % of price	Approximate cap rate
6	1.39%	10.1%
8	1.04%	7.6%
10	0.83%	6.1%
12	0.69%	5.1%
15	0.56%	4.1%
20	0.42%	3.0%

The 1% rule, monthly rent at 1% of price, is a GRM of 8.3 and a cap rate around 7.3% under these assumptions. That is why the rule roughly identifies properties that cash flow with a normal loan.

When GRM is enough

Screening a list. If you are looking at forty listings, computing NOI for each is not worth the time. GRM sorts them in seconds, and in a market where expense ratios are similar across properties, the sort order will match cap rate closely.

Comparing similar properties in one market. Two single-family houses in the same county with similar taxes and no HOA will have nearly proportional expenses. Their GRMs rank them as well as their cap rates would.

Quick sanity checks. A GRM of 18 in a market where everything trades at 10 tells you something is off before you open the spreadsheet.

When GRM fails

Whenever expenses differ between the properties you are comparing. The common cases:

HOA dues. A condo at $2,500 rent with $400 monthly dues has the same GRM as a house at $2,500 rent with none. Its NOI is $4,800 lower. On a $300,000 price that is 1.6 points of cap rate GRM cannot see.

Property taxes. Effective tax rates range from under 0.5% to over 2% of value across states. On $300,000 that is a $4,500 annual swing, or 1.5 points of cap rate, between two properties with identical rent and price.

Insurance. Coastal, wildfire and flood zones can run two to three times the premium of inland properties.

Utilities. A multifamily where the owner pays heat and water versus one where tenants do can differ by 10% of rent.

Age and condition. An 1920s building with a 12% maintenance load and a 2015 build at 5% look identical on GRM.

Across markets, GRM is nearly useless for this reason. A GRM of 10 in a 0.6% tax state and a GRM of 10 in a 2.2% tax state are properties with cap rates roughly 1.6 points apart.

Using both

Screen with GRM. Underwrite with cap rate. A reasonable workflow:

1. Sort listings by GRM or rent-to-price. Discard anything far outside the range you need.
2. For the survivors, build a real NOI: taxes after reassessment, real insurance quotes, HOA, vacancy, maintenance, reserves and management.
3. Compute cap rate and compare to recent sales in the submarket.
4. Add your financing and compute cash on cash to see whether you can hold it.

The calculator shows GRM and rent-to-price alongside the cap rate on every run, so the shortcut and the full answer sit next to each other. When they disagree, the cap rate is right and the GRM is telling you the expenses are unusual.

A note on gross yield

Some listings quote a gross yield, annual rent divided by price. It is the inverse of GRM: a GRM of 10 is a 10% gross yield. It is not a cap rate, though it is sometimes labeled as one. Treat any yield above 9% on a residential listing as a prompt to check whether expenses were included. The cap rate formula guide covers what belongs in NOI.