When analyzing the terms of a loan, it is important to consider more than the interest rate. Two loans can have identical principal amounts, interest rates and repayment lengths but significant differences in the amount of interest you pay, especially if one loan uses simple interest and the other uses compound interest. Simple interest is calculated using only the principal balance of the loan. With compound interest, the interest per period is based off the principal balance plus any outstanding interest already accrued. Interest compounds over time.
The Truth in Lending Act (TILA) requires that lenders disclose loan terms to potential borrowers, including the total dollar amount of interest to be repaid over the life of the loan and whether interest accrues simply or is compounded. Besides scrutinizing the Truth in Lending statement, a quick mathematical calculation tells you whether you are looking at simple or compound interest.
Suppose you borrow $10,000 at a 10% annual interest rate with the principal and interest due as a lump sum in three years. Using a simple interest calculation, 10% of the principal balance gets added to your repayment amount during each of the three years. That comes out to $1,000 per year, which totals $3,000 in interest over the life of the loan. At repayment, then, the amount due is $13,000.
Now suppose you take out the same loan, with the same terms, but the interest is compounded annually. The first year, the interest rate of 10% is calculated only from the $10,000 principal. Once that is done, the total outstanding balance, principal plus interest, is $11,000. The difference kicks in during the second year. The interest for that year is based off the full $11,000 that you currently owe, rather than just the $10,000 principal balance. At the end of year two, you owe $12,100, which becomes the base for the thirdyear interest calculation. When the loan is due, instead of owing $13,000, you end up owing $13,310. While you may not consider $310 a huge difference, this example is only a threeyear loan; compound interest piles up and becomes oppressive with longer loan terms.
Another factor to watch for is how often interest is compounded. In the above example, it is once per year. However, if it is compounded more frequently, such as semiannually, quarterly or monthly, the difference between compound and simple interest increases. More frequent compounding means the base from which new interest charges are calculated increases more rapidly.
One more simple method to determine if your loan uses simple or compound interest is to compare its interest rate to its annual percentage rate, which the TILA also requires lenders to disclose. The annual percentage rate (APR) converts the finance charges of your loan, which include all interest and fees, to a simple interest rate. A substantial difference between the interest rate and the APR means one or both of two things: your loan uses compound interest, or it includes hefty loan fees in addition to interest.

What formula calculates interest on interest?
Find out about compounding interest, what it measures, and how to calculate the amount of compound interest accrued using ... Read Answer >> 
How to calculate compound loan interest in Excel?
Find out about compound interest and how to use the compounding interest formula in Microsoft Excel to calculate the compound ... Read Answer >>

Investing
Understanding the Power of Compound Interest
Understanding compound interest is important for both investing and borrowing money. 
Investing
Learn simple and compound interest
Interest is defined as the cost of borrowing money or the rate paid on a deposit to an investor. Interest can be classified as simple interest or compound interest. 
Investing
Continuous compound interest
Different frequency in compound interest results in different returns. Check out how continuous compounding accelerates your return. 
IPF  Banking
How Interest Rates Work on Savings Accounts
Here's what you need to know to grow your rainyday fund. 
Investing
Overcoming Compounding's Dark Side
Understanding how money is made and lost over time can help you improve your returns. 
Managing Wealth
Unsecured Personal Loans: 8 Sneaky Traps
If you are seeking a personal loan, be aware of these pitfalls before you proceed. 
IPF  Banking
The Interest Rates: APR, APY and EAR
When most people shop for financial products, all they focus on is the listed interest rate. Human eyes instinctively dismiss the fine print, which usually includes the terms APR (annual percentage ... 
Investing
How to calculate your investment return
How much are your investments actually returning? The method of calculation can make a significant difference in your true rate of return. 
Insights
Forces Behind Interest Rates
Get a deeper understanding of the importance of interest rates and what makes them change.

Periodic Interest Rate
The periodic interest rate is the interest rate charged on a ... 
Compound
Compound is the ability of an asset to generate earnings, which ... 
Effective Annual Interest Rate
The effective annual interest rate is an investment's annual ... 
Compounding
Compounding is the process in which an asset's earnings, from ... 
Interest Cost
Interest cost refers to the cumulative amount of interest a borrower ... 
AddOn Interest
Addon interest is an alternative method of calculating interest ...