How to calculate commercial mortgage payment

The most common mistake in commercial real estate is assuming a commercial mortgage payment works like a residential one, a fixed 30-year amortization with no balloon, which is why it is essential to understand how to calculate commercial mortgage payment correctly. That is wrong for most deals. Commercial loans typically run 5 to 10 years with a balloon payment due at maturity, amortized over 25 to 30 years. To work out or verify a payment by hand or in a spreadsheet, you need the commercial mortgage payment formula, which is the mathematical engine behind every amortization schedule. The formula is derived from the present value of an annuity: it calculates a payment that, at the monthly interest rate, exactly pays off both the interest accrued each month and the principal over the loan term. The (1 + r)^n term represents the growth of the loan if no payments were made, which is why compounding matters.

The standard monthly payment for a fully amortizing commercial mortgage is: M = P × [r(1 + r)^n] / [(1 + r)^n - 1], where P is the principal, r is the monthly interest rate (annual rate divided by 12), and n is the total number of payments (amortization term in months). For a $1,000,000 loan at 6% annual interest over 25 years (300 payments), r = 0.005 and n = 300.The full calculation yields approximately $6,443.01 per month. Do not trust mental math here; use the formula or a spreadsheet.

This works because the formula rearranges the present value of an annuity. Each payment covers the interest that has accrued since the last payment, and the remainder reduces the principal. As the principal shrinks, the interest portion of each payment drops, and the principal portion rises. Over the full term, the payments exactly amortize the loan to zero. Understanding this helps you see how changes in loan terms affect your payment: a longer amortization lowers the payment but increases total interest; a higher rate raises the payment; a balloon payment at the end changes the future value calculation. The commercial mortgage payment formula is not optional for anyone pricing a deal, it is the baseline against which every other metric, from DSCR to cash-on-cash return, is measured.

Here is the step-by-step process to calculate a payment by hand, using a realistic retail example. Take a $750,000 loan at 5.25% annual interest, amortized over 20 years (240 months). First, convert the annual rate to a monthly rate: 5.25% / 12 = 0.004375. Second, determine the number of payments: 20 years × 12 = 240. Third, plug into the formula: M = P × [r(1 + r)^n] / [(1 + r)^n, 1]. Compute (1.004375)^240. Using a calculator, that is approximately 2.8532. The numerator becomes 0.004375 × 2.8532 = 0.0124828. The denominator is 2.8532-1 = 1.8532. Divide: 0.0124828 / 1.8532 = 0.006735. Multiply by the principal: 0.006735 × $750,000 = $5,051.25 per month.

Check the math against a known good example. The difference comes from rounding the exponent too early. Always carry at least six decimal places in the monthly rate and use a scientific calculator or spreadsheet for the exponent. If you are doing it by hand, use logarithms or a table of powers, but honestly, the risk of arithmetic error is high. That is why the commercial loan payment formula is best executed in a tool that handles precision, not in your head.

When the loan has a balloon payment, say, a 10-year term on a 25-year amortization, the step-by-step changes. You still calculate the monthly payment using the full 25-year amortization, but at month 120, you owe the remaining principal. To find that balance, use the formula for the future value of an amortizing loan: B = P × [(1 + r)^n, (1 + r)^m] / [(1 + r)^n, 1], where m is the number of payments made. For a $750,000 loan at 5.That balloon amount is what you must refinance or pay off at maturity. The standard formula gives the payment; the balloon requires a separate calculation. Do not skip this step, most commercial loans are balloons, and ignoring the future value is how investors get caught short.

Interest-only (IO) loans are common in commercial real estate, especially for bridge financing or when a borrower wants to maximize cash flow in the early years. The calculation is simpler than the full amortization formula: the monthly payment is simply the principal multiplied by the monthly interest rate. For a $1,000,000 loan at 6% annual interest, the monthly rate is 0.005, and the payment is $1,000,000 × 0.005 = $5,000 per month. That is it, no exponents, no compounding, no principal reduction. The commercial mortgage payment formula for IO is P × r, where r is the monthly rate. You can do this in your head or on the back of an envelope.

But the simplicity hides a serious risk. The interest-only trap works like this: a borrower takes an IO loan at 75% loan-to-value (LTV), the property value drops 10%, and the balloon cannot be refinanced because the LTV is now 83%. The borrower never paid down any principal, so there is no equity cushion. When the IO period ends, typically 3 to 5 years, the loan converts to a fully amortizing payment, which can jump 30% to 50% overnight. That payment shock is a leading cause of commercial mortgage defaults. If you are considering an IO loan, run the numbers both ways: what is the payment during the IO period, and what will it be when amortization kicks in? The difference is the risk you are taking.

For IO loans with a balloon, the calculation is even more stark. The payment during the IO period is just the interest, and at maturity, you owe the full principal. There is no future value calculation because the balance never changes. This is fine if the property appreciates or you have a refinance lined up, but it is a bet on the market. The commercial loan payment formula for IO is the easiest math in real estate, yet it is also the most dangerous because it lulls borrowers into thinking they can afford a payment that will not stay constant. Always stress-test an IO loan against a fully amortizing scenario before you commit.

The spreadsheet is where the commercial loan payment formula becomes a tool you can use in seconds. In Excel or Google Sheets, the PMT function calculates the monthly payment directly. The syntax is =PMT(rate, nper, pv, [fv], [type]). For a $750,000 loan at 5.25% annual interest over 25 years, the formula is =PMT(5.25%/12, 25*12, 750000). The rate argument is the monthly rate (annual rate divided by 12), the nper argument is the total number of payment periods (25*12 = 300), and the pv argument is the present value or principal of the loan. The result is a negative number because it represents cash paid out, about -$4,494.21 per month. That is the payment for a fully amortizing 25-year loan, not a 20-year one, so it is lower than the hand calculation above.

To break down the payment into interest and principal, use the IPMT and PPMT functions. =IPMT(rate, period, nper, pv) gives the interest portion for a specific period; =PPMT gives the principal. For example, =IPMT(5.25%/12, 1, 300, 750000) returns the interest for the first payment, about -$3,281.25. The PPMT for the same period is the difference: -$1,212.96. These functions are essential for building an amortization schedule, which shows exactly how much of each payment goes to interest versus principal over the life of the loan. You can drag the formulas down 300 rows to see the full schedule, or you can stop after the first few periods to understand the trend.

For a balloon payment, the FV function is your friend. The syntax is =FV(rate, nper, pmt, [pv], [type]). To find the balance after 120 payments on a 300-payment amortization, use =FV(5.25%/12, 120, -4494.21, 750000). The result is negative because it is a cash outflow at the end, about -$586,000. That is the balloon amount due. The FV function result sign convention is negative because it represents cash paid out, which can be confusing. Multiply by -1 to get a positive number if you prefer. The PMT result sign convention is similarly negative. If you are using the pmt excel commercial loan function, remember that the pmt argument in the FV formula must be the payment you calculated with PMT, not the interest-only amount, unless the loan is IO. For an IO loan, the balloon is just the original principal, so FV is unnecessary, the balance never changes.

One nuance: the type argument in PMT and FV controls whether payments are made at the beginning or end of each period. 0 (the default) means end of period; 1 means beginning. Most commercial mortgages use end-of-period payments, so leave it blank or set it to 0. If you set it to 1, the payment will be slightly lower because interest accrues for one less period. Also, be aware that the actual/360 interest calculation is standard in commercial real estate, meaning interest accrues on the actual number of days in the month, divided by 360. This can make the effective monthly payment slightly different from the PMT function's output, which assumes a 30/360 convention. For a $500,000 loan at 6%, the difference is about $2.50 per month, small, but it adds up over a year. If you want precision, use the actual day count in your spreadsheet, but for most underwriting, the PMT function is close enough.

The most frequent error in calculating commercial mortgage payments is using the wrong term. A 5-year balloon on a 25-year amortization means you calculate the payment over 300 months, not 60. The payment is based on the amortization schedule, not the loan term. If you use 60 months, the payment will be far too high, and you will underestimate your cash flow. The second most common mistake is confusing the annual rate with the monthly rate. Always divide by 12 before plugging into the formula. A 6% annual rate is 0.5% per month, not 6% per month. Third, forgetting the balloon entirely. Many borrowers calculate the payment correctly but ignore the lump sum due at maturity. That balloon is not optional, it is a debt obligation that must be refinanced or paid in cash.

Another error is using the wrong future value in the PMT function. If you are pricing a loan with a balloon, you can include the future value as a negative number in the PMT formula to get the correct payment. For example, =PMT(5.25%/12, 120, 750000, -586000) gives the payment for a 10-year term with a balloon. But this is not the standard approach, most lenders quote the payment based on the full amortization and handle the balloon separately. The risk is that you quote a payment that is too low because you ignored the balloon's impact on the lender's required yield. Lenders do not lose money on balloons; they price the rate to reflect the refinancing risk. If you are the borrower, you should do the same.

Finally, do not trust a calculator that does not show its assumptions. Many online commercial mortgage calculators default to a 30-year amortization, which is rare in commercial real estate. A 25-year amortization is more common, but 20-year and even 15-year amortizations exist, especially for smaller loans. Always check the amortization term, the interest rate, and the balloon period before you rely on the output. If the tool does not let you input all three, find another tool. The commercial mortgage payment formula is only as good as the inputs you feed it. Garbage in, garbage out, and in commercial real estate, garbage can cost you six figures.

Rates move daily, and the commercial mortgage payment formula must be recalculated every time the market shifts. Do not assume the rate you were quoted last month is still available.That is why you need to know how to calculate commercial mortgage payment yourself, not rely on a broker's quote that may be stale. The formula is the same regardless of the rate; only the inputs change. If you are comparing two loans, one at 5.5% and one at 6.0%, run both through the formula before you sign anything. The difference in payment is the cost of the higher rate, and you should know exactly what it is.

When the amortization term changes, the payment moves too.Shortening from 25 to 15 years raises the payment by 34% but saves a fortune in interest. The commercial loan payment formula shows this trade-off clearly: the longer the term, the lower the payment, but the more you pay in total.That is the kind of number you need to see before you choose a term.

Balloon risk is the third variable. A 10-year balloon on a 25-year amortization is the most common structure for permanent commercial mortgages. The payment is manageable, but the balloon is a cliff. If rates have risen by the time the balloon comes due, your refinancing payment could be 20% higher. Run the FV function in Excel to see the balloon amount, then stress-test it: what is the payment if you have to refinance at 200 basis points higher? If you cannot make that payment, you need to lock in a longer term or a lower rate now. The formula does not care about your exit strategy; it just computes the numbers. You have to be the one who plans for the worst case.

Sometimes the standard formula does not apply because the loan is not a simple amortizing mortgage. A floating-rate loan with a rate cap, for example, has a payment that changes every month based on SOFR or the Prime rate. The commercial mortgage payment formula assumes a fixed rate, so you cannot use it directly. Instead, you must project the rate over the life of the loan, which is an educated guess at best. The failure case here is the borrower who locks in a floating-rate loan without stress-testing the payment at the cap. When rates rise, the payment jumps, and the property's net operating income (NOI) may not cover it. The DSCR, which was 1.30x at the initial rate, drops to 0.95x at the cap. That is a default waiting to happen.

Another scenario where the formula fails is a loan with a payment that is not fully amortizing but has a negative amortization feature, the payment is less than the interest, and the shortfall is added to the principal. This is rare in commercial real estate but not unheard of in bridge loans. The formula will give you the payment for a fully amortizing loan, but the actual payment is lower, and the balance grows over time. If you use the standard formula, you will overestimate the payment and may think the deal does not work. But the real risk is the growing balance, which can push the LTV above 100% by maturity. The failure case is the borrower who takes a negative amortization loan to make the numbers work, only to find the balloon cannot be refinanced because there is no equity.

When you hit these edge cases, the spreadsheet is still your friend, but you need to model the actual cash flows, not rely on a single formula. Build a monthly cash flow model that inputs the rate, the amortization, the balloon, and the interest-only period, and let Excel compute the payment for each period. Use the IPMT and PPMT functions to track the balance over time. The PMT function works for fixed-rate loans; for floating-rate, you have to build a separate schedule. And if you are in over your head, hire a commercial mortgage broker who has a model that handles these scenarios. The cost of a broker is 1% of the loan amount, but the cost of a wrong payment calculation is the property itself.

Scenario	Rate	Amortization	Term	Monthly Payment	Balloon Due at Maturity
Fixed, Fully Amortizing	5.25%	20 years	20 years	$6,726	$0
Fixed, Balloon	5.25%	25 years	10 years	$5,994	$586,000
Interest-Only	6.00%	N/A	5 years IO	$5,000	$1,000,000
Floating Rate (at cap)	8.00%	25 years	10 years	$7,718	$586,000

The monthly payment is just the starting point. The commercial mortgage payment formula gives you the debt service, but it does not tell you whether the property can support it. That is what the debt service coverage ratio (DSCR) measures: net operating income divided by the annual debt service. Lenders want a DSCR of at least 1.25x for a stabilized property, meaning the NOI covers the payment by 25%. If the payment is $4,494 per month, the annual debt service is $53,928. You need NOI of at least $67,410 per year to hit 1.25x. If the property only generates $60,000, you have a problem, the payment is too high for the income. The formula is agnostic; it does not care about the property's performance. You have to do that analysis separately.

The payment also ignores the all-in cost of the loan, which includes origination fees, appraisal, legal, and title. Lenders quote a rate, but no one publishes the all-in cost as an annual percentage. For a $1 million loan, origination fees of 1% add $10,000 to the cost, which is equivalent to 0.10% per year over a 10-year term. Appraisal and legal add another $5,000 to $10,000. When you compare two loans, one at 5.5% with 1% origination and another at 5.75% with no fees, the effective rate may be lower for the second loan, even though the nominal rate is higher. The commercial loan payment formula cannot capture this. You have to calculate the effective rate, which requires an IRR or a modified formula that includes the fees as a negative cash flow at closing.

Finally, the payment does not account for the actual/360 interest calculation that most commercial mortgages use. Under this convention, interest accrues on the actual number of days in the month, divided by 360. A 31-day month accrues more interest than a 30-day month, so the monthly payment can vary by $10 to $20 for a $500,000 loan. Over a year, that is $120 to $240 in extra interest. It is not a huge number, but it is real money. The PMT function assumes a 30/360 basis, so the actual payment will be slightly different. To get the true payment, you need to calculate the daily interest rate (annual rate / 360), multiply by the actual days in the month, and add that to the principal reduction. Most borrowers do not bother, and lenders do not volunteer the difference. But if you are pricing a deal to the penny, you need to know.

The commercial mortgage payment formula is universal, but the inputs are not. In Canada, commercial mortgage terms are similar to the U.S., 5-year balloons on 25-year amortizations, but the benchmark is the 5-year Government of Canada bond, not the 10-year Treasury. Prepayment penalties in Canada are typically the greater of 3 months' interest or the interest rate differential, which can be brutal in a falling rate environment. The formula is the same, but the rate you plug in is different. In the European Union, the Mortgage Credit Directive applies to residential, not commercial, mortgages, so commercial lending is less regulated. Rates are often quoted as a margin over EURIBOR, and the payment can float. You cannot use the standard formula for a floating-rate loan without projecting the rate, which adds uncertainty.

There is no global standard for commercial mortgage underwriting, so the formula is the only constant. In Australia, commercial loans often have a 15-year term with a 30-year amortization, and the payment is calculated monthly. In the UK, the typical commercial mortgage is a 25-year amortization with a 5-year rate fix, after which the rate resets. The formula does not change; the rate does. If you are pricing a deal in a foreign market, you need to know the local convention for the day count, the rate index, and the prepayment penalty. The actual/360 convention is standard in the U.S., but the UK uses actual/365, which changes the daily interest rate.25x DSCR.

The failure case is the borrower who assumes a U.S.-style loan in a foreign market. They calculate the payment using a 30/360 convention, but the lender uses actual/365, and the payment comes out higher. Or they assume a 10-year Treasury is the benchmark, but the local market uses a 5-year swap rate, and the rate is 50 basis points higher. The formula is not wrong; the inputs are. Always ask the lender for their exact day count convention and rate index before you run the numbers. And if you are doing a cross-border deal, hire a local broker who knows the market. The formula is the easy part; the conventions are where the money is made and lost.

A $1,000,000 loan at 7% over 25 years gives a payment of about $7,067, because (1.0058333)^300 is approximately 5.725, not 5.743.