# How is compound interest different from simple interest?

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## Introduction

Compound interest and simple interest are two different methods used to calculate the interest on a loan or an investment. While both methods involve earning interest on a principal amount, they differ in terms of how the interest is calculated and the impact it has on the overall growth of the investment or debt.

## Compound Interest

Compound interest is a method of calculating interest where the interest earned is added to the principal amount, and subsequent interest is calculated based on the new total. In other words, interest is earned on both the initial principal and the accumulated interest. This compounding effect allows the investment or debt to grow at an accelerated rate over time.

The formula for calculating compound interest is:

A = P(1 + r/n)^(nt)

Where:
A = the future value of the investment or debt
P = the principal amount
r = the annual interest rate (expressed as a decimal)
n = the number of times the interest is compounded per year
t = the number of years

For example, if you invest \$1,000 at an annual interest rate of 5% compounded annually for 5 years, the future value of the investment would be calculated as:

A = 1000(1 + 0.05/1)^(1*5)
A = 1000(1 + 0.05)^5
A = 1000(1.05)^5
A = 1000(1.27628)
A = \$1,276.28

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As you can see, the interest earned in each year is added to the principal amount, resulting in a higher future value compared to simple interest.

## Simple Interest

Simple interest, on the other hand, is a method of calculating interest where the interest earned is based only on the initial principal amount. In simple interest, the interest earned remains constant throughout the investment or debt period and is not added to the principal.

The formula for calculating simple interest is:

I = P * r * t

Where:
I = the interest earned
P = the principal amount
r = the annual interest rate (expressed as a decimal)
t = the number of years

Using the same example as before, if you invest \$1,000 at an annual interest rate of 5% for 5 years, the interest earned would be calculated as:

I = 1000 * 0.05 * 5
I = \$250

The future value of the investment would be the sum of the principal and the interest earned:

A = P + I
A = 1000 + 250
A = \$1,250

As you can see, with simple interest, the interest earned remains constant throughout the investment period, resulting in a lower future value compared to compound interest.

## Difference between Compound Interest and Simple Interest

The key difference between compound interest and simple interest lies in how the interest is calculated and the impact it has on the overall growth of the investment or debt. Compound interest allows for exponential growth as the interest earned is added to the principal, resulting in a higher future value over time. Simple interest, on the other hand, results in linear growth as the interest earned remains constant throughout the investment period.

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In practical terms, compound interest is commonly used in investments such as savings accounts, bonds, and long-term loans. It allows for the growth of the investment to accelerate over time, maximizing returns. Simple interest, on the other hand, is often used in short-term loans or situations where the interest rate is low and the investment period is short.

## Conclusion

In summary, compound interest and simple interest are two different methods used to calculate interest. Compound interest involves earning interest on both the principal amount and the accumulated interest, resulting in exponential growth. Simple interest, on the other hand, calculates interest based only on the principal amount, resulting in linear growth. The choice between compound interest and simple interest depends on the specific investment or debt and the desired growth or cost structure.

## References

– Investopedia: www.investopedia.com
– The Balance: www.thebalance.com