It is the payment of an amount over the principal sum by a borrower or deposit-taking financial institution to a lender or depositor at a specific rate

Author: Elliot Meade
Elliot Meade
Elliot Meade
Private Equity | Investment Banking

Elliot currently works as a Private Equity Associate at Greenridge Investment Partners, a middle market fund based in Austin, TX. He was previously an Analyst in Piper Jaffray's Leveraged Finance group, working across all industry verticals on LBOs, acquisition financings, refinancings, and recapitalizations. Prior to Piper Jaffray, he spent 2 years at Citi in the Leveraged Finance Credit Portfolio group focused on origination and ongoing credit monitoring of outstanding loans and was also a member of the Columbia recruiting committee for the Investment Banking Division for incoming summer and full-time analysts.

Elliot has a Bachelor of Arts in Business Management from Columbia University.

Reviewed By: Manu Lakshmanan
Manu Lakshmanan
Manu Lakshmanan
Management Consulting | Strategy & Operations

Prior to accepting a position as the Director of Operations Strategy at DJO Global, Manu was a management consultant with McKinsey & Company in Houston. He served clients, including presenting directly to C-level executives, in digital, strategy, M&A, and operations projects.

Manu holds a PHD in Biomedical Engineering from Duke University and a BA in Physics from Cornell University.

Last Updated:November 29, 2023

What Is Interest?

Interest is the payment of an amount over the principal sum by a borrower or deposit-taking financial institution to a lender or depositor at a specific rate. This amount is generally levied on borrowed money or money that's on credit. 

The rate of return is equivalent to the amount of (charged) rate paid or earned over a fixed period by the principal sum borrowed or lent, commonly presented in terms of percentage.

The rate value varies from profit as the ante money is paid to a lender, whereas profit is paid to the proprietor of an asset, property, commodity, or enterprise. Nevertheless, it is generally proportioned to an investment at a fixed rate. 

It may also be defined as the revenue gained from the holding of contractual obligations to repay the money in the future made by others.

Understanding Interest

The choice to pay it is determined according to what you receive in exchange, whereas the option to earn money over a lump sum amount is determined by the other possibilities for investing your money.

1. When Borrowing Money

When you borrow funds/cash, you must pay the principal sum to the creditor/bank. 

You will also be expected to pay the loan's lending rate to your creditor as you must remunerate your lender for the risk that they have taken up on your loan and the fact that they cannot spend and use that money while you have it. 

Examples of this are credit cards, vehicle loans, mortgages, personal investment loans, or other types of debt you may come across.

For example, let's say you need to borrow $200,000 from your bank for a simple house loan with an annual borrowing rate of 6% and a 15-year repayment period. 

Typically compounded monthly, the borrowing rate on a conventional house loan is added to monthly payments. Over the course of the loan, you would pay nearly $180,000 over the borrowed amount in this case.

2. When Lending Money

If you do have surplus cash on hand, you may invest it yourself or deposit the money in a savings account, allowing the bank to lend it out or invest it. But, again, you'll predict receiving a regular return on your investment. 

Credit score and debt-to-income ratio are common indicators banks use to set your rate. Commercial lenders typically add additional costs for creating a client loan.

For example, let's say that you have deposited $50,000 in your bank's savings account (a time deposit account) for one year with a guaranteed rate of return of 1% per annum. After 12 months, you can withdraw your $50,000 and receive an interest of $500. 

3. Factors that affect the Rates & Payments

The rate of return depends on what kind of debt has been opted for and what costs are incurred.

A. Installment Debt: 

The charges of loans such as a traditional house, vehicle, and student loan are incorporated into your periodic payment.

Each month, a piece of your overhead payment goes toward debt reduction, while another amount goes toward the cost of bearing risk on the money lent. You pay off your debt over a certain length of time using these loans.

For example, a 20-year mortgage.

B. Revolving Debt:

Some loans allow you to borrow more monthly money and repay it over time since they are revolving loans. For instance, as long as you don't exceed your credit limit, credit cards enable you to make recurring transactions, or bank overdraft facilities for businesses allow short-term credit on a monthly or quarterly basis

Types Of Interests and Their Calculation

The types and calculations are:

1. Simple Interest (SI)

Is the rate charged on the principal or the remaining fraction of the original amount?

SI can be imposed over a defined time, such as a year or every month. Therefore SI is the product of the principal sum, the loan period, and the rate charged. It does not have a compounding factor to it. 

In a loan with SI, the payment proceeds to clear up the interest payment for that month, and the rest is transferred to the principal. The rate charged never builds up since it is always paid and accounted for monthly.

Auto loans and short-term personal loans often have SI. Most loans with SI are also mortgages with amortization of intangible assets.

Savings accounts and other nest-egg accounts generate earnings because you allow the bank to use your funds as collateral for loans to others, which is calculated using SI.

Mathematically speaking

SI = P × T × R / 100

  • SI - the rate charged on the principal 
  • P - Principal Sum 
  • T - Period (in years or T/12 for months or T/365 for days calculation)
  • R - Rate of interest (R% or R/100)

Consider investing $10,000 (the principle) at a rate of 5% per year. The formula for calculating SI is:

After a year, $10,000 multiplied by (5/100) will yield $500 in SI.


SI = $ (10,000 × 1× 0.05) = $ 500

Keep in mind that the rate charged on the capital is expressed as 5/100 or 0.05. You must convert percentages to decimals to perform your computations.

SI loans are frequently available when you need to purchase a new asset but have poor credit, so you won't have to worry about delayed payments, and you do not have to pay the accrued interest on top of the existing one you owe the creditor.

2. Compound Interest (CI)

The rate charged on a loan or deposit computed using the original principle and the accrued interest from prior periods is known as compound or CI. 

Compared to SI, which is computed just on the principal amount, CI, this will cause a sum to rise more quickly.

The compounding frequency determines the pace at which the compounded return accumulates; the more compounding periods, the higher the rate charges.

When calculating CI, the starting principal amount is multiplied by one, and the yearly rate is raised to the number of compound periods minus one. The whole initial loan amount then reduces the resultant value.

Mathematically speaking

The formula yields the entire cumulative value, which includes the principal amount "P" and CI "I."

Over here:

A = [P (1 + i)^n] 


 CI = [P (1 + i)^n] – P  


 CI = (A - P)


  • A - total sum earned
  • P - principal sum
  • I - borrowing/lending rate
  • N - the required period of time

Suppose a principal amount of a has-been deposited $15,000 in a bank that pays an annual rate of return of 5%, compounded annually for four years.

Then the balance after 4 years is found by using the formula above, with 

P = $15,000, r = 0.05 (5%), n = 4

A = [15,000 (1 + 0.05)4] = $ 18,232.6

CI = $ (18,232.6 - 15,000) = $ 3,232.6

Your wealth increases more quickly due to CI. Because you will receive returns on your investment after each compounding period, it causes an amount of money to grow more rapidly than with SI. 

As a result, you won't need to save as much money to achieve your financial objectives. 

what Is Accrued Interest?

In accounting, the prime rate has been accrued on the loan over time but has not yet been paid or collected by the debtor or creditor.

Regardless of when the cash transactions are received, accrual-based accounting mandates that revenues and costs be recognized in the accounting period in which they are incurred. 

Compared to the cash-based system, the accrual-based accounting method correctly displays a company's financial situation.

AI is a crucial factor to consider when buying or selling a bond. Bonds provide monthly interest payments as repayment for the money borrowed from the owner. These prime rate payments, sometimes known as coupons, are typically made twice a year or half-yearly.

The accrued rate is shown on the income statement as a turnover or expenditure depending on whether the corporation wants to lend or borrow. 

Additionally, an asset or liability is shown on the balance sheet for the amount of revenue or cost that has not yet been paid or collected. 

Accrued rate of borrowing charges is frequently categorized as a current asset or current debt since it is anticipated to be earned or paid within a financial year.

For example, think about a company that borrows money to buy machinery. On the first day of the next month, the business must pay interest to the bank for that machine. 

The firm can utilize that specific equipment to do business and make income because the company used it for the prior month. 

The company will have to keep track of the prime rate, and it plans to pay out the next day at the end of every month. Furthermore, because the bank expects the borrower to pay it the next day, it will also record AI returns for the same one-month period.

How does Interest affect the National Economy?

Rates of Interest considerably impact economic decisions and performance in every country where the market plays a critical part. They affect the inclination to save and the demand for and distribution of loaned money.

Are affected:

However, borrowing the prime / bank rate differs between emerging and developed economies due to disparities in the development of their financial system, the separation of saving and investment choices, and the flexibility granted for capital.

The rate at which funds can be borrowed is relatively less critical in nations with extensive non-monetized sectors than in highly monetized economies, and they have a much less direct effect in centrally planned economies than are market-oriented.

The rate for borrowing money is relatively less critical in nations with extensive non-monetized sectors than in highly monetized economies, and they have a much less direct effect in non-capitalist societies than in market-oriented economies.

Fluctuations in prime rates are integral in preserving the equilibrium between demand and supply in goods and money markets in market-oriented economies where most saving and investment decisions are made separately, provided that the institutional environment permits such changes.

Even in capitalistic economies or nations with less developed financial markets, authorities must consider the rates of return on alternative projects and the social cost of money used to finance them to distribute scarce resources efficiently.

Several emerging economies set significant bank rates officially, which are generally enforced by law as price ceilings (highest possible limit) on loan and deposit rates.

The aim of rate regulation in developing nations is that a few significant banks can control the financial systems, and the rate of return on borrowed money gets easily influenced.

The rate of return significantly impacts aggregate demand / final domestic demand.

Salaries highly influence this rate, currency exchange rates, labor generation & unemployment, deposited savings & investments, and the cash & credit circulation ratio in the economy.

Economists suggest that finance costs should be kept low. 

Low prime rates in emerging economies encourage a higher degree of investment. 

How Does interest Affect GDP

Low prime rate charges give most people a lesser propensity to save money, which minimizes the amount of money available for loans, creating the desired investment greater than the actual investment. 

Thus, even while it somewhat lowers desired investment, an increase in bank rates may result in a greater level of the actual investment. 

The appeal of the overall economic environment is negatively impacted by capital outflows, currency shortages, and poor projected returns to investment projects that typically occur with low prime rates, which may also boost desired investments as expected rates of return increase.

The rate of return affects the capacity of a nation's central bank to retain control over the rate of internal credit growth, public sector income and expenditure, and the trade deficit.

A hike in the real rate of return boosts the motivation to save since the return for saving is greater. As a result, economic savings are anticipated to rise, reducing demand and consumption.

Thus, an increase in the rate of return raises the cost of borrowing and the cost of capital expenditure. This phenomenon inhibits firms from investing, and as a result, the overall investment in the economy diminishes. 

Hence we see that an increase in rates causes a decrease in Real GDP

Researched & Authored by Aviral Mathur | LinkedIn

Free Resources

To continue learning and advancing your career, check out these additional helpful WSO resources: