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Interest Rate Formula


Introduction to interest rate formula:

In this article we discuss the interest rate formula. The annual percentage of the principal amount is represented as interest rate. The interest rate can be charged not only for year. It can be charged every month or every week or every six months. Sometimes the interest rate can be charged every day. The interest rate can be classified into two types,

Simple interest rate
Compound interest rate.

Some Important Formulas for Interest Rate:

Simple interest formula:

Simple interest rate SI=PNR

Where

P=Principal amount

N=Period of Time

R=Rate of the interest

We are knows the simple interest SI then we can find the P, N and R using the same simple interest formula.

First we can find P, We are using the formula is,

Principal amount `P=I/"NR"`

Next we can find N, We are using the formula is,

Period of time `N=I/"PR"`

Finally we can find R, We are using the formula is,

Rate of the interest `R=I/"PN"`

Compound interest rate formula:

Compound interest `CI=P (1+R/100) ^N`

Where

P=Principal amount

N=Period of time

R=Rate of the interest

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Example Problems for Interest Rate Formula:

Problem 1:

John paid $4000 at 30% after 6 years in finance. To find the simple interest and compound interest.

Solution:

Here,

Principal amount P = $4000

Period N = 6years

Interest rate R = 30%

Simple interest SI = PNR

`SI =4000*6*30/100`

=7200

Simple interest = 7200

Compound interest `CI=P (1+R/100) ^N`

` CI = 4000( 1+30/100)^6`

`=4000( 130/100 )^6`

` =4000(13/10 )^6`

`=4000(4826809/ 1000000)`

`= 19307236/1000`

CI = 19307.236

Total amount of simple interest = 4000+7200

=11200

Total amount of compound interest=19307.236

Problem 2:

Vicky paid $1000 at 5% after 3years in finance. To find the simple interest and compound interest.

Solution:

Here,

Principal amount P = $1000

Period N =3years

Interest rate R= 5%

Simple interest SI = PNR

`SI =1000*3*5/100`

=150

Simple interest = 150

Compound interest `CI=P (1+R/100) ^N`

`CI = 1000( 1+5/100)^3`

`=1000( 105/100 )^3`

` =1000(21/20 )^3`

` =1000(9261/ 8000)`

CI = 1157.625

Total amount of simple interest = 1000+150

=1150

Total amount of compound interest=1157.625

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