## What Is Simple Interest?

Simple interest is a quick and easy method of calculating the interest charge on a loan. Simple interest is determined by multiplying the daily interest rate by the principal by the number of days that elapse between payments.

$\begin{aligned} &\text{Simple Interest} = P \times I \times N\\ &\textbf{where:} \\ &P = \text{principle} \\ &I = \text{daily interest rate} \\ &N = \text{number of days between payments} \\ \end{aligned}$

This type of interest usually applies to automobile loans or short-term loans, although some mortgages use this calculation method.

#### Understanding Simple Interest

## Understanding Simple Interest

When you make a payment on a simple interest loan, the payment first goes toward that month’s interest, and the remainder goes toward the principal. Each month’s interest is paid in full so it never accrues. In contrast, compound interest adds some of the monthly interest back onto the loan; in each succeeding month, you pay new interest on old interest.

To understand how simple interest works, consider an automobile loan that has a $15,000 principal balance and an annual 5-percent simple interest rate. If your payment is due on May 1 and you pay it precisely on the due date, the finance company calculates your interest on the 30 days in April. Your interest for 30 days is $61.64 under this scenario. However, if you make the payment on April 21, the finance company charges you interest for only 20 days in April, dropping your interest payment to $41.09, a $20 savings.

### Key Takeaways

- Simple interest is calculated by multiplying the daily interest rate by the principal, by the number of days that elapse between payments.
- Simple interest benefits consumers who pay their loans on time or early each month.
- Auto loans and short-term personal loans are usually simple interest loans.

## Who Benefits From a Simple Interest Loan?

Because simple interest is calculated on a daily basis, it mostly benefits consumers who pay their loans on time or early each month. Under the scenario above, if you sent a $300 payment on May 1, then $238.36 goes toward principal. If you sent the same payment on April 20, then $258.91 goes toward principal. If you can pay early every month, your principal balance shrinks faster, and you pay the loan off sooner than the original estimate.

Conversely, if you pay the loan late, more of your payment goes toward interest than if you pay on time. Using the same automobile loan example, if your payment is due on May 1 and you make it on May 16, you get charged for 45 days of interest at a cost of $92.46. This means only $207.54 of your $300 payment goes toward principal. If you consistently pay late over the life of a loan, your final payment will be larger than the original estimate because you did not pay down the principal at the expected rate.

## What Types of Loans Use Simple Interest?

Simple interest usually applies to automobile loans or short-term personal loans. Most mortgages do not use simple interest, although some banks use this method for mortgages for bi-weekly payment plans. Bi-weekly plans generally help consumers pay off their mortgages early because the borrowers make two extra payments a year, saving interest over the life of the loan by paying off the principal faster. (For related reading, see "4 Ways Simple Interest Is Used in Real Life")