How to Calculate Commercial Loan Interest: Simple, Amortized, and Daily Methods

Interest: Simple and Compound

Interest on a loan can be calculated in different ways. Commercial loans often use an amortizing structure, where each monthly payment covers both interest and a portion of the principal. The interest portion is recalculated based on the outstanding balance, which decreases over time. This method differs from simple interest, which is based on the original principal, and from compound interest, which adds accumulated interest to the principal.

This guide explains how interest is calculated in common commercial loan structures, using formulas for fully amortizing and interest-only loans. It also covers the difference between fixed and variable rates, which affect how much interest you pay over time.

Sources: Mortgage Calculator, Janover Pro

Calculating Simple Interest on a Loan

Simple interest is calculated only on the original principal amount borrowed. The formula is: Interest = Principal × Rate × Time. This method is straightforward but does not account for principal reductions from payments.

For interest-only loans, the monthly interest payment is calculated as: Loan Amount × (Annual Rate / 12). This formula charges interest on the full loan amount each month, similar to simple interest over a short period.

Simple interest calculations are most appropriate for short-term loans or lines of credit, where the principal is not amortized. However, most commercial mortgages use amortizing payments to reduce the principal over time.

• Simple interest formula: Interest = Principal × Rate × Time.
• Interest-only payment formula: Loan Amount × (Annual Rate / 12) for monthly payments.

Sources: Mortgage Calculator, Janover Pro

Interest in Amortized Payments

Most commercial mortgages are fully amortizing, meaning that the loan is paid off over the amortization period with equal monthly payments that include both principal and interest. The formula for the monthly payment on a fully amortizing loan is: Monthly Payment = L × [r(1+r)^n] / [(1+r)^n - 1], where L is the loan amount, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments.

For example, a $1,000,000 loan at 6.5% interest with a 25-year amortization period would have a monthly principal and interest payment of approximately $6,752. This payment covers both the interest on the outstanding balance and a portion of the principal, so the loan is fully paid off by the end of the 25 years.

Sources: Janover Pro

Daily Simple Interest for Commercial Loans

Some commercial loans use a daily simple interest method, where interest accrues daily on the outstanding principal balance. The daily interest amount is calculated as: Daily Interest = Outstanding Balance × (Annual Rate / 365). This amount is added to the loan balance until a payment is made.

This method is often used for lines of credit, where the borrower draws funds and pays interest on the amount actually used. Because interest accrues daily, the total interest paid depends on how often payments are made and the timing of those payments.

Sources: Janover Pro

Rate Type: Fixed and Variable

Commercial loan interest rates can be fixed or variable. Fixed interest rates keep the same interest rate and monthly payment for the life of the loan, providing payment stability. Variable interest rates fluctuate over time based on a benchmark, such as the prime rate, causing monthly payments to change.

Fixed-rate loans generally have a higher interest rate than variable-rate loans, while variable-rate loans often start with a lower rate. For example, SBA 504 loans always have a fixed interest rate, which is set based on the market rate for 5 and 10-year U.S. Treasury issues. In contrast, many commercial banks offer variable rates.

The choice between fixed and variable rates affects your total interest paid. A fixed rate protects you from rate increases but may cost more if rates fall. A variable rate can save money if rates stay low but can increase your payments if rates rise. Consider your cash flow stability and expectations for future rate movements.

Sources: TMC Financing, Live Oak Bank

Example Calculations for Each Method

To illustrate, let's compare the interest calculations for a $1,000,000 loan at a 6.5% annual interest rate using different methods.

For a 25-year fully amortizing loan, the monthly payment is approximately $6,752.

If the loan is interest-only for the first year, the monthly payment would be $1,000,000 × (0.065 / 12) = $5,417.

Sources: Janover Pro