Annual debt service is the total amount of principal and interest a borrower pays on a loan across a 12-month period. If your commercial mortgage payment is $5,000 a month, your annual debt service is $60,000. The figure matters most in commercial lending, where it sits at the center of the debt service coverage ratio lenders use to decide whether a property generates enough income to carry the loan.
What Counts, and What Doesn’t
Only two things go into the number: the principal payments that reduce your loan balance and the interest payments that compensate the lender. Add them up for every scheduled payment in a year and you have annual debt service.
What sits outside the calculation is just as important. Prepayment penalties, yield maintenance fees, and balloon payments due at maturity are excluded. Escrow contributions for property taxes and insurance are also excluded, even though your lender may collect them alongside the mortgage payment. The figure captures the cash that either pays down what you owe or pays for the privilege of owing it. Nothing else.
How to Calculate Annual Debt Service
The math is simple once you know how the loan is structured. The complication is that identical loan amounts and interest rates can produce very different annual debt service numbers depending on the payment structure.
Fully Amortizing Loans
On a fully amortizing loan, each payment covers both principal and interest, and the total payment amount is fixed. Multiply the monthly payment by 12.
Take a $1,000,000 commercial mortgage at a fixed 6% annual rate with a 25-year amortization. The monthly payment works out to roughly $6,443. Multiply by 12 and annual debt service is about $77,318. That number holds for the life of the loan absent refinancing or extra payments. Fannie Mae’s standard approach for amortizing loans is exactly this: the monthly payment stated in the note, multiplied by 12.1Fannie Mae. Debt Service Coverage Ratio (DSCR) Examples
Interest-Only Loans
Interest-only structures are common in bridge loans and construction financing. During the interest-only period no principal is paid, so the calculation is: loan balance times annual interest rate.
The same $1,000,000 loan at 6% produces annual debt service of $60,000 during its interest-only period, or $5,000 a month. Compared with the $77,318 on the fully amortizing version, the lower figure is exactly what makes interest-only loans attractive up front.1Fannie Mae. Debt Service Coverage Ratio (DSCR) Examples
The tradeoff is that you still owe the full $1,000,000 when the interest-only period ends. The loan either converts to full amortization over the remaining term, with sharply higher payments, or comes due as a balloon.
Variable-Rate Loans
When the interest rate floats, actual annual debt service moves with it. Lenders don’t underwrite to the current rate. They calculate debt service at the maximum note rate allowed under the loan agreement, which builds in a cushion against future increases. If your adjustable-rate loan has a lifetime cap of 9%, the lender sizes the loan as though you’re paying 9% even if today’s rate is 5.5%.2Fannie Mae. Calculating the Debt Service – Fannie Mae Multifamily Guide
Rate floors set a minimum you’ll pay even if the benchmark index drops below them, so your annual debt service can’t fall past a certain level. Ceilings cap the other direction. Together they define the band inside which your real annual debt service will land.
More Than One Loan on the Property
Many properties carry more than one loan, particularly when an owner adds a supplemental mortgage after the original financing closes. Total annual debt service in that case is just the sum of the annual debt service on each loan. Lenders evaluate the combined figure against the property’s income.
Why Lenders Care: The Debt Service Coverage Ratio
Annual debt service exists as a working concept largely because of the debt service coverage ratio. Divide the property’s net operating income (NOI) by its annual debt service. If NOI is $100,000 and annual debt service is $77,318, the DSCR is about 1.29.1Fannie Mae. Debt Service Coverage Ratio (DSCR) Examples
That 1.29 tells the lender the property earns $1.29 for every $1.00 owed in debt payments, a 29-cent cushion per dollar. Most commercial lenders require a minimum DSCR around 1.25. Fannie Mae uses a 1.25 threshold for standard multifamily loans.3Fannie Mae. Near-Stabilization Execution Term Sheet
Higher-risk property types like hotels or specialized industrial buildings often carry a 1.35 minimum. SBA loans may accept a DSCR as low as 1.15 because the government guarantee reduces the lender’s exposure. The specific threshold depends on the lender, the loan program, and the deal’s risk profile.
A DSCR of exactly 1.0 means income only just covers debt payments with no margin. No institutional lender accepts that. Below 1.0 and the property is losing money after debt service, meaning you’d need to cover the shortfall from other sources every month.
Some lenders on smaller commercial loans also calculate a global DSCR, which folds in your total income from all sources (personal income and other properties included) and measures it against your total debt obligations everywhere. That version tests whether your overall financial strength can absorb a bad month at a single property.
How Annual Debt Service Caps Your Loan Size
The DSCR requirement works backward to limit how much you can borrow. The lender starts with your property’s NOI, divides by the required DSCR, and gets the maximum annual debt service the loan can carry. From there, they calculate the largest loan that produces payments at or below that ceiling.
An example makes the mechanics clear. Your property has an NOI of $150,000 and the lender requires a 1.25 DSCR. Maximum annual debt service is $150,000 รท 1.25 = $120,000. At a 6% rate with 25-year amortization, that $120,000 supports a loan of roughly $1,550,000. Move the required DSCR to 1.35 and maximum annual debt service falls to about $111,111, which shrinks the supportable loan to around $1,435,000. A $115,000 swing in loan size comes entirely from the coverage requirement tightening by a tenth.
Small errors in the annual debt service calculation cascade directly into how much you can borrow and whether a deal works.
How Debt Service Is Taxed
The two pieces of annual debt service are treated very differently at tax time. Interest is generally deductible as a business expense, so the after-tax cost of debt service is lower than the nominal figure. Federal tax law allows a deduction for interest paid on business indebtedness.4Office of the Law Revision Counsel. 26 USC 163 – Interest
For rental property, you deduct mortgage interest on Schedule E. The IRS treats it as an ordinary expense of the rental activity.5Internal Revenue Service. Instructions for Schedule E (Form 1040)
The principal portion is never deductible. Repaying borrowed money isn’t an expense, so it carries no tax benefit. When you project after-tax cash flow, only the interest piece reduces taxable income.
Larger businesses face an added constraint. Under Section 163(j), the deduction for business interest is capped at 30% of adjusted taxable income, though small businesses meeting a gross receipts threshold are exempt.6Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense
Net Operating Income Sits Behind the Whole Calculation
Annual debt service ultimately has to be paid from the property’s cash flow, and the standard measure of that cash flow is net operating income. NOI is gross rental revenue minus operating expenses like property taxes, insurance, utilities, and management fees. It deliberately excludes income taxes and debt service, because lenders want a clean read on what the property itself earns before any financing decision is made.5Internal Revenue Service. Instructions for Schedule E (Form 1040)
When NOI comfortably exceeds annual debt service, the difference is your levered cash flow, the actual return that reaches your pocket after paying the lender. When NOI barely exceeds debt service, a single month of vacancy or an unexpected repair can push the property into the red. Building a real cushion into the projection, rather than sizing to the minimum DSCR, is how you keep a temporary dip from becoming a covenant problem later.