Simple Interest

What is Simple Interest

Simple interest is the method of calculating the interest amount for some principal amount of money. Simple interest formula in maths helps you to find the interest amount if the principal amount, rate of interest and time periods are given. The S.I formula used for same is = (P × R × T) / 100.  Another type of interest is compound interest.

The major difference between simple and compound interest is that simple interest is based on the principal amount of a deposit or a loan whereas the compound interest is based on the principal amount and interest that accumulates in every period of time.

Simple Interest Example

Have you ever borrowed money from your siblings when your pocket money got exhausted? Or lent him maybe? What happens when you borrow money? You use that money for the purpose you had borrowed it in the first place. After that, you return the money whenever you get the next month’s pocket money from your parents. This is how borrowing and lending work at home.

But in the real world, money is not free to borrow. You often have to borrow money from banks in the form of a loan. During payback, apart from the loan amount, you pay some more money that depends on the loan amount as well as the time for which you borrow. This is called simple interest. This term finds extensive usage in banking.

SI Formula

  • Principal or Sum: The money that is lent or borrowed.
  • Interest: It is the money paid in addition to the principal.
  • Rate: It is the percentage of principal paid as interest.
  • Time: It is the duration for which the principal is borrowed.
  • Amount: It is the total money paid back at the end of the time period for which it was borrowed. It is given by-

Amount (A) = Principal (P) + Interest (I)

Simple Interest Formula

Simple interest formula is given as

SI = (P × R ×T) / 100

Where SI = simple interest

P = principal

R = interest rate (in percentage)

T = time duration (in years)

Simple Interest Problems

Let us see some of the simple interest examples using simple interest formula in maths.

  • Rishav takes a loan of Rs 10000 from a bank for a period of 1 year. The rate of interest is 10% per annum. Find the interest and the amount he has to the pay at the end of a year.


Here, the loan sum = P = Rs 10000

Rate of interest per year = R = 10%

Time for which it is borrowed = T = 1 year

Thus, simple interest for a year,  SI = (P × R ×T) / 100 = (1000× 100 ×1) / 100 = Rs 1000

Amount that Rishav has to pay to the bank at the end of the year = Principal + Interest = 10000 + 1000 = Rs 11,000

  • Namita borrowed Rs 50,000 for 3 years at the rate of 3.5% per annum. Find the interest accumulated at the end of 3 years.


P = Rs 50,000

R = 3.5%

T = 3 years

 SI = (P × R ×T) / 100 = (50,000× 3.5 ×3) / 100 = Rs 5250 

  • Mohit pays Rs 9000 as an amount on the sum of Rs 7000 that he had borrowed for 2 years. Find the rate of interest.


A = Rs 5000

P = Rs 7000

SI = A – P = 7000 – 5000 = Rs 2000

T = 2 years

R = ?

SI = (P × R ×T) / 100 

R = (SI  × 100) /(P× T)

R = (2000  × 100 /7000 × 2)  =14.29 % 

Thus R  = 14.29%