Mortgage Constant Commercial Real Estate

Mortgage constant commercial real estate analysis is a one-line ratio that tells you how heavy the debt is before you debate the interest rate. The mortgage constant equals annual debt service divided by the loan amount. Compare that percentage with the property’s cap rate. When the cap rate is higher than the constant, debt can lift the return on equity. When the cap rate is lower, debt can drag the equity return down even if the building is full. Investors who skip this comparison often discover leverage in the first year of ownership, when the cash flow is already committed.

The figures below are illustrations, not a rate quote and not terms you can expect. An inquiry is not an approval.

Mortgage Constant Commercial Real Estate Is Annual Debt Service Over the Loan

Write it as a fraction.

Mortgage constant = annual debt service ÷ loan amount

Annual debt service means the actual principal and interest you will pay over a year on that loan. Taxes and insurance are property costs. They belong in net operating income or in a residential PITIA figure. They are not part of the constant unless you are mixing ratios on purpose and then comparing them to the wrong cap rate.

Illustration: a $1,000,000 loan with annual principal and interest of $80,000 has a mortgage constant of 8.0 percent. You do not need the note rate to compute it once you know the payment. The rate, the amortization, and any interest-only period are already inside the $80,000. A longer amortization lowers the annual payment and lowers the constant. An interest-only period lowers it further until principal starts, and then the constant jumps. That jump is why an interest-only teaser should be underwritten on the payment you will have when the IO period ends, not only on the opening year.

The constant is not the interest rate. An interest-only loan at 8 percent has a constant near 8 percent because you pay interest and no principal. An amortizing loan at a lower note rate can have a constant near 8 percent because principal is in the payment. Comparing note rates without the constant hides that. Two term sheets with the same interest rate and different amortization are different constants and different cash flows.

Market yields that feed loan pricing are published in places such as the Federal Reserve’s H.15 selected interest rates. You still compute the constant from your payment, not from a Treasury yield. H.15 tells you the backdrop. The note tells you the numerator.

Put the Constant Next to the Cap Rate

The cap rate is net operating income divided by value (or price). If you are buying at $1,000,000 and stabilized NOI is $90,000, the cap rate is 9 percent. If NOI is $70,000, the cap rate is 7 percent. How NOI is built for a loan file is its own discipline. See how to calculate NOI for a commercial loan.

The classic screen:

Comparison	What it suggests
Cap rate above the mortgage constant	Each dollar of debt costs less than the NOI yield on the asset. Leverage can raise cash yield on equity.
Cap rate equal to the constant	Debt is neutral on that simple screen. Fees, vacancy, and reserves still matter.
Cap rate below the mortgage constant	Debt costs more than the asset yields. Leverage can reduce the equity return. That is negative leverage.

Using the illustrations above, a 9 percent cap against an 8 percent constant is the favorable side of the screen. A 7 percent cap against the same 8 percent constant is the unfavorable side. This comparison is cleanest as a warning light. It is not a full partnership waterfall. It ignores loan fees, capital expenditures below NOI, and the fact that you rarely borrow 100 percent of the price. At a lower loan-to-value, part of the price is equity that does not “pay” the constant. The direction of the screen still matters. Borrowing a slice at a constant above the cap rate pulls cash yield toward that more expensive slice.

Cap rate versus DSCR is the sibling test. DSCR asks whether NOI covers the payment by a margin, such as 1.25 times. The constant asks whether the payment’s percentage cost is above or below the asset’s yield. A file can show a DSCR above 1.00 because you put a large down payment in, and still show a constant above the cap rate on the dollars you did borrow. Both numbers belong on the page. Commercial DSCR explains the coverage ratio lenders actually use. Do not substitute one for the other.

A Worked Purchase

Price $2,000,000. NOI $140,000. Cap rate 7.0 percent. Proposed loan $1,400,000. Annual debt service $112,000. Mortgage constant = 112,000 ÷ 1,400,000 = 8.0 percent.

Cash flow after debt service = 140,000 − 112,000 = $28,000. Equity = $600,000. Cash-on-cash = 28,000 ÷ 600,000 = 4.7 percent. The equity yield is below the 7 percent cap rate. The constant (8 percent) sat above the cap rate (7 percent), and the simple screen was right: leverage diluted the unlevered yield. DSCR = 140,000 ÷ 112,000 = 1.25, so a lender’s coverage test might still look acceptable. Coverage and equity yield answered different questions. You can “qualify” and still have made the equity return worse than buying with less debt.

Change only the price. Same NOI, price $1,750,000, cap rate 8.0 percent. Same loan constant of 8 percent on whatever you borrow is now a tie with the cap rate, before fees. The building did not change. What you paid did. Overpaying is how investors manufacture a bad constant comparison in a market where debt is not actually expensive relative to a sensible price.

If you want the algebra of a weak equity return when debt outruns the asset, read negative leverage next to this page. The constant is the measurement. Negative leverage is the result of ignoring it.

What Changes the Constant After Closing

The constant is not frozen just because you remember the rate.

• A rate reset on a floating loan changes the payment and the constant. A cap on the rate, if you bought one, limits that move and has its own cost.
• The end of interest-only raises the payment. Recompute the constant on the amortizing payment before you call year-one cash flow “stabilized.”
• A partial prepayment or a holdback release changes the loan balance. The constant uses the loan amount in the denominator. Be consistent about which balance you mean.
• A supplemental or second lien has its own constant. Blended debt cost is the weighted figure, not the first mortgage alone.

Recalculate when the payment changes. A constant you computed at application and never revisited is how a refinance surprise shows up as “the building got worse” when the building did not. The payment did.

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Frequently Asked Questions

Is the mortgage constant the same as the interest rate?

No. The interest rate is the note rate, and the mortgage constant is annual principal and interest divided by the loan amount. An amortizing loan’s constant is higher than its note rate because principal is in the payment, while an interest-only constant sits close to the note rate. Compare constants when the amortization differs, and compare note rates only when the structure is the same.

Should I compare the constant to the cap rate or to cash-on-cash?

Start with cap rate versus constant as the leverage screen, then compute cash-on-cash on the equity you actually write. The first shows whether debt is cheaper or more expensive than the asset yield. The second shows what your cash earns after the down payment.

Do taxes and insurance go in the mortgage constant?

No. Use principal and interest in the numerator, and let taxes, insurance, and utilities affect NOI or the cash you keep. Mixing operating costs into the constant and then comparing it with a cap rate double-counts those costs. Keep the two ratios pure so the screen means something.

Can a high constant still be acceptable?

Yes, if you are borrowing less, if signed leases will lift NOI, or if you can fund thin cash flow while principal paydown does the work. The constant flags the drag and does not forbid the loan. Be honest that you are choosing tight leverage, and hold reserves to match.

Does a favorable constant guarantee a loan or a rate?

No. The constant is your math on a payment you illustrated or were shown, and lenders still test coverage, value, sponsorship, and the property. This page does not quote rates. Divide the real annual payment by the loan amount and compare that constant with the cap rate at your price.