Before you take out a bank loan, you need to know how your interest rate is calculated. There are many methods banks use to calculate interest rates and each method will change the amount of interest you pay. If you know how to calculate interest rates, you will better understand your loan contract with your bank. You are also in a better position to negotiate your interest rate with your bank. Banks will quote you the effective rate of interest. The effective rate of interest is also known as the annual percentage rate (APR). The APR or effective rate of interest is different than the stated rate of interest. Banks also tie your interest rate to a benchmark, usually the prime rate of interest.

**Effective Interest Rate on a one Year Loan**

If you borrow $1000 from a bank for one year and have to pay $60 in interest for that year, your stated interest rate is 6%. Here is the calculation:

**Effective Rate on a Simple Interest Loan = Interest/Principal = $60/$1000 = 6%**

Your annual percentage rate or APR is the same as the stated rate in this example because there is no compound interest to consider. This is a simple interest loan.

**Effective Interest Rate on a Loan With a Term of Less Than one Year**

If you borrow $1000 from a bank for 120 days and the interest rate is 6%, what is the effective interest rate?

Effective rate = Interest/Principal X Days in the Year (360)/Days Loan is Outstanding

**Effective rate on a Loan with a Term of Less Than one Year=$60/$1000 X 360/120 = 18%**

**Effective Interest Rate on a Discounted Loan**

Some banks offer discounted loans. Discounted loans are loans that have the interest payment subtracted from the principal before the loan is disbursed.

Effective rate on a discounted loan = Interest/Principal - Interest X Days in the Year (360)/Days Loan is Outstanding

**Effective rate on a discounted loan=$60/$1,000 - $60 X 360/360 = 6.38%**

As you can see, the effective rate of interest is higher on a discounted loan than on a simple interest loan.

**Effective Interest Rate with Compensating Balances**

Some banks require that the small business firm applying for a business bank loan hold a balance, called a compensating balance, with their bank before they will approve a loan. This requirement makes the effective rate of interest higher.

Effective rate with compensating balances (c) = Interest/(1-c)

**Effective rate compensating balance= 6%/(1 - 0.2) = 7.5% (if c is a 20% compensating balance)**

**Effective Interest Rate on Installment Loans**

One of the most confusing interest rates that you will hear quoted on a bank loan is that on an installment loan. Installment loan interest rates are generally the highest interest rates you will encounter. Using the example from above:

Effective rate on installment loan = 2 X Annual # of payments X Interest/(Total no. of payments + 1) X Principal

**Effective rate/installment loan=2 X 12 X $60/13 X $1,000 = 11.08%**

The interest rate on this installment loan is 11.08% as compared to 7.5% on the loan with compensating balances.

Here's an example of a loan amortization schedule for a bank installment loan.