For example,4000 dollars is deposited into a bank account and the annual interest rate is 8%.

How much is the interest after 4 years?

Use the following simple interest formula:

I = p× r × t

where p is the principal or money deposited

r is the rate of interest

t is time

We get:

I = p× r × t

I = 4000× 8% × 4

I = 4000× 0.08 × 4

I = 1280 dollars

However, coumpound interest is the interest earned not only on the original principal, but also on all interests earned previously

In other words, at the end of each year, the interest earned is added to the original amount and the money is reinvested

If we use compound interest for the situation above, the interest will be computed as follow:

Interest at the end of the first year:

I = 4000× 0.08 × 1

I = 320 dollars

Your new principal per say is now 4000 + 320 = 4320

Interest at the end of the second year:

I = 4320× 0.08 × 1

I = 345.6 dollars

Your new principal is now 4320 + 345.6 = 4665.6

Interest at the end of the third year:

I = 4665.6× 0.08 × 1

I = 373.248 dollars

Your new principal is now 4665.6 + 373.248 = 5038.848

Interest at the end of the fourth year:

I = 5038.848 × 0.08 × 1

I = 403.10784 dollars

Your new principal is now 5038.848 + 403.10784 = 5441.95584

Total interest earned = 5441.95584 − 4000 = 1441.95584

The difference in money between coumpond interest and simple interest is 1441.96 - 1280 = 161.96

As you can see, compound interest yield better result, so you make more money.

Therefore, before investing your money, you should double check with your local bank if coumpound interest will be used.

Having said that if you have a credit card and you owe money on it, you will pay less interest if the credit card company uses simple interest. However, they will never do something so foolish!

I hope simple vs compound interest is well understood now!

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