How to Calculate Commercial Mortgage Payments

How to Calculate Commercial Mortgage Payments Step by Step

Calculating a commercial mortgage payment by hand might seem daunting, but it's straightforward once you understand the formula. This guide walks you through the process so you can verify your numbers before using the Commercial Mortgage Calculator for faster results. If you need a refresher on the basics, read our article on what is a commercial mortgage.

You'll Need:

• Loan amount (P) – Property purchase price minus down payment. Commercial loans typically require 20–35% down.
• Annual interest rate – Typical range 5–9% for commercial properties.
• Amortization period (in years) – How long to fully repay the loan (e.g., 20 or 25 years). Note: this may differ from the loan term, which can be shorter with a balloon payment.
• Calculator or spreadsheet – For exponents; manual multiplication works too.

Step-by-Step Process

1. Calculate the loan amount (P). Subtract your down payment from the property purchase price. Example: $2,000,000 purchase with 25% down ($500,000) gives P = $1,500,000.
2. Convert annual interest rate to a monthly rate (r). Divide the annual rate by 12. For 6% annual, r = 0.06 ÷ 12 = 0.005.
3. Determine total number of monthly payments (n). Multiply amortization years by 12. For 20 years, n = 20 × 12 = 240.
4. Apply the monthly payment formula. M = P × [ r(1+r)^n ] ÷ [ (1+r)^n – 1 ]. Compute (1+r)^n, then multiply by r, divide by [(1+r)^n – 1], then multiply by P.
5. Check your work. Use our formula explained page for detailed derivations.

Worked Example 1: Office Building

Assumptions: Purchase price = $2,000,000; Down payment = 25% ($500,000); Loan amount (P) = $1,500,000; Annual interest = 6%; Amortization = 20 years.

• Monthly rate r = 0.06/12 = 0.005
• Number of payments n = 20 × 12 = 240
• Calculate (1+r)^n = (1.005)^240. Using a calculator: ≈ 3.3102
• Numerator: r × (1+r)^n = 0.005 × 3.3102 = 0.016551
• Denominator: (1+r)^n – 1 = 3.3102 – 1 = 2.3102
• Monthly payment M = $1,500,000 × (0.016551 / 2.3102) = $1,500,000 × 0.007164 ≈ $10,746

So the monthly payment is about $10,746. Compare this with our payment ranges page to see if it fits typical benchmarks.

Worked Example 2: Retail Space

Assumptions: Purchase price = $1,200,000; Down payment = 30% ($360,000); Loan amount (P) = $840,000; Annual interest = 7%; Amortization = 25 years.

• Monthly rate r = 0.07/12 = 0.00583333
• Number of payments n = 25 × 12 = 300
• (1+r)^n = (1.00583333)^300. Using a calculator: ≈ 5.743
• Numerator: 0.00583333 × 5.743 = 0.0335
• Denominator: 5.743 – 1 = 4.743
• Monthly payment M = $840,000 × (0.0335 / 4.743) = $840,000 × 0.007062 ≈ $5,932

Common Pitfalls

• Using loan term instead of amortization. Many commercial loans have a 5-10 year term but 20-30 year amortization. The monthly payment depends on the amortization period, not the term. The remaining balance is due as a balloon payment.
• Forgetting to convert the annual rate to monthly. Always divide by 12.
• Rounding too early. Keep several decimal places during intermediate steps to avoid errors.
• Excluding other costs. Your actual monthly outlay may include property taxes, insurance, and reserves – this calculation covers only principal and interest.

Now you can confidently calculate commercial mortgage payments by hand. For quick analysis on multifamily properties, see our multifamily property guide. And if you have further questions, check our FAQ page.