Interest Rate Formula

Formula to Calculate Interest Rate

An interest rate formula is used to calculate the repayment amounts for loans and interest over investment on fixed deposits, mutual funds, etc. It is also used to calculate interest on a credit card.

When a lender lends any amount to the borrower for a specific time period known as the principal amount over that lender charge interest, that percentage of principle is known as the interest rate. In simple words, the interest rate is the rate at which the lender charges the amount over principle landed by the lender. The interest rate is directly proportional to risk as there is risk involved when a lender lends an amount to the borrower. It is also called compensation of opportunity lost.

In terms of investment, interest is paid on bank deposit investment like fixed deposit, recurring deposit, and even on the amount deposited in saving bank account. Bank pays interest half-yearly on saving account deposits. In contrast, for fixed deposit and recurring deposit, interest paid based on customer request, which could be monthly, quarterly, half annually, or yearly. And interest rate applied for one year is the annual interest.

There are two types of interest rate formula:-

Simple Interest Rate Formula

Simple interestSimple InterestSimple interest (SI) refers to the percentage of interest charged or yielded on the principal sum for a specific more is levied when a loan is borrowed for one year or less. Simple interest is generally applied for the short term.

Simple Interest Rate = (Principle * Rate of Interest * Time Period (years))/ 100

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For eg:
Source: Interest Rate Formula (

In simple in it also written as,

Simple Interest rate = (P*R*T)/100

You can download this Interest Rate Formula Excel Template here – Interest Rate Formula Excel Template


A borrower borrows $1000 from a lender for 9 months and at an interest rate of 12%. Now, we will calculate the simple interest rate of interest to be paid to a lender on a principal amount of $1000.

  • Simple Interest
Interest rate formula 1

The interest payableInterest PayableInterest Payable is the amount of expense that has been incurred but not yet paid. It is a liability that appears on the company's balance more to the lender is $90, and the principal amount is $1000. The total amount payable to a lender is $1090.

total amount payable

Compound Interest Formula

Compound interest Compound Interest Compound interest is the interest charged on the sum of the principal amount and the total interest amassed on it so far. It plays a crucial role in generating higher rewards from an moreis called “interest on interest.” It is calculated on the principal amount, and of the time period, it changes with time.

The time period, it changes with time.

Compound Interest Rate = P (1+i) P


  • P = Principle
  • i= Annual interest rate
  • t= number of compounding period for a year
  • i =  r
  • n = number of times interest is compounded per year
  • r = Interest rate (In decimal)

Total amount payable to be lender = P (1+i) t


A borrower took a personal loan from ABC bank, he borrowed $5000 amount from a bank at the interest rate of 10%, for a time period of 5 years, compounded yearly then compound interest will be:

  • Compound Interest
compound interest calculation

So from the above calculation of Compound Interest will be:

compound interest

Use and Relevance

  • An interest rate formula helps one to understand loan and investment and take the decision. These days financial bodies like banks use the Compound interest formula to calculate interest. Compounded annual growth rate, i.e., CAGR, is used mostly for financial applications where single growth for a period needs to be calculated.

Recommended Articles

This article has been a guide to Interest Rate Formula. Here we discuss how to calculate Simple and Compound Interest Rate in Excel using practical examples and downloadable templates. You can learn more about financial analysis from the following articles –

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