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    Compound Interest Formula

    Gone are the days of school mathematics, most of us easily forget, but a quick refresher may bring it all back. To understand compound interest in the easiest form, let’s take a look at what it means. Compound interest is a useful financial concept in which your interest earned is added to your principal. This amount then continues to earn more interest. So in this case, you also earn interest on the interest you’ve already earned. So your balance grows at an increasing rate. In a sense, you reinvest your interest, rather than receiving a pay-out.

    • Year 1 - You earn interest on your Principal.
    • Year 2 - You earn interest on your (Principal + Interest of Year 1).
    • Year 3 - You earn interest on your (Principal + Interest of Year 1 + Interest of Year 2).

    Compound interest is the basis of long-term growth of the stock market. It forms the basis of personal savings plans. Compound interest also affects inflation.

    Types of Compound Interest

    There are generally two types of compound interest used.

    • Periodic Compounding - Under this method, the interest rate is applied at intervals and generated. This interest is added to the principal. Periods here would mean annually, bi-annually, monthly, or weekly.
    • Continuous Compounding - This method uses a natural log-based formula and calculates interest at the smallest possible interval. This interest is added back to the principal. This can be equalled to the constant rate of growth for all natural growth. This figure was born out of physics. It uses Euler’s number which is a famous irrational number which is known to more than 1 trillion digits of accuracy. Euler’s number is denominated by the letter “E”.

    Periodic Compound Interest Formula Overview

    There are two formulas you can use to calculate compound interest, depending on what result you wish to find out. You can find out the following:

    • The total value of the deposit.
    • The total compound interest earned.

    Value of the Deposit

    Formulas can be a deterrent to many. If you aren’t savvy with math, your eyes turn away from these codes or just skip them altogether. But once it’s explained, it’s pretty simple to understand. To calculate the total value of your deposit, the formula is as follows:

    P (1+ i/n)nt

    P = Principal invested.

    i = Nominal Rate of Interest.

    n = Compounding Frequency or number of compounding periods in a year.

    t = Time, meaning the length of time the interest is applicable, generally in years.

    Simply put, you calculate the interest rate divided by the number of times in a year the compound interest is generated. For instance, if your bank compounds interest quarterly, there are 4 quarters in a year, so n = 4. This result must be multiplied to the power of the deposit period. For example, if your deposit is for 10 years, t = 10. This whole result should be multiplied by the principal you invested. The result generated will equal the total accumulated value of your deposit. You can find out how much your deposit is worth currently after accumulating interest.

    Total Compound Interest Earned

    To find out how much interest was earned, you can use the following formula for Compound Interest.

    P[(1+ i/n))nt-1]

    Compound Interest Equation and Calculation

    To understand the compound interest equation further, we can break it down in simpler terms. If you decide to invest in a fixed deposit with compound interest, this is how you will earn interest every year.

    Period Deposit Balance
    Investment P
    Year 1 P + iP
    Year 2 (P+ iP) + i(P+iP)

    To collapse this formula, we can pull out factors of (1+i). Simply substitute iP with (1+i) to get the following:

    Period Deposit Balance
    Investment P
    Year 1 P(1+i)
    Year 2 P(1+i)2
    Year 3 P(1+i)3

    Formula for Annual Compound Interest

    To calculate the compound interest for a number of years together, we need to multiply P(1+i) to the power of the number of years of the deposit. So we end up with this formula:

    P (1+ i/n)n

    This formula can be used to calculate compound interest that is compounded annually. This means you receive interest only once a year. It is added to your principal, and you continue to earn interest on the new amount.

    Half-Yearly, Quarterly, Monthly Compound Interest Formula

    If you are earning interest multiple times in a year, you need to factor in this number into the equation. So the formula generated is:

    P (1+ i/n)nt

    This formula can also be used for instances where the interest is compounded once every two years. In this case, n = 0.5, as each year is calculated as half.

    Examples of Compound Interest

    For example, Rs. 10,000 is invested in a fixed deposit for 10 years. The interest is compounded every quarter which means 4 times in a year. The interest paid by the bank is 5%. To find out your nominal rate of interest, you need to divide 5 by 100 which equals 0.05. Now, we look at the formula and substitute the letters with the relevant numbers.

    Calculating the Total Value of the Deposit

    P (1+ i/n)nt

    Step 1: 10,000 (1+0.05/4)4x10

    Step 2: 10,000(1+0.0125)40

    Step 3: 10,000 (1.0125)40

    Step 4: 10,000 (1.64361946349)

    Step 5: 16436.1946349

    We can round of this total to Rs. 16,436.19. So the compound interest earned after 10 years is Rs. 6,436.19.

    Calculating the Interest Earned

    We can also arrive at this figure using the formula for compound interest earned. We can substitute the numbers for letters as seen below:

    P[(1+ i/n)nt -1]

    Step 1: 10,000 [(1+0.05/4)4x10 -1]

    Step 2: 10,000 [(1+0.0125)40-1]

    Step 3: 10,000 [(1.0125)40-1]

    Step 4: 10,000 [(1.64361946349) -1]

    Step 5: 10,000 (0.664361946349

    Step 5: 6436.1946349

    We can now add this interest earned to the principal amount to find out the value of the deposit. The maturity value will be Rs. 16,436.19.

    The earnings through compound interest can be demonstrated with the following graph.

    FD Compund Interest

    Simple Interest vs. Compound Interest

    To demonstrate the difference between simple interest and compound interest, let’s take for example two fixed deposits. Both deposits are of Rs. 10,000 for 10 years. The interest offered on Deposit 1 is 5% compound interest. The interest offered on Deposit 2 is 5% simple interest. The interest is calculated annually on both deposits.

    Period Deposit 1 - Compound Interest Deposit 2 - Simple Interest Difference
    Year 1 Rs. 500 Rs. 500 Rs. 0
    Year 2 Rs. 1,025.00 Rs. 1,000 Rs. 25
    Year 3 Rs. 1,576.25 Rs. 1,500 Rs. 76.25
    Year 4 Rs. 2,115.06 Rs. 2,000 Rs. 115.06
    Year 5 Rs. 2,762.82 Rs. 2,500 Rs. 762.82
    Year 6 Rs. 3,400.96 Rs. 3,000 Rs. 400.96
    Year 7 Rs. 4,071.00 Rs. 3,500 Rs. 571.00
    Year 8 Rs. 4,774.55 Rs. 4,000 Rs. 774.55
    Year 9 Rs. 5,513.28 Rs. 4,500 Rs. 1,013.28
    Year 10 Rs. 6,288.95 Rs. 5,000 Rs. 1,288.95
    FD Comparison

    From the graph above, we can see clearly the higher earnings through compound interest compared to simple interest. The difference is not too much upto the 4th year. This is because the interest accumulated over the years is added to the principal, thus making the principal significantly higher. From Year 5, there is a major difference in the interest earned. At the end of 10 years, Deposit 1 earns Rs. 6,288.95, while Deposit 2 earns Rs. 5,000. The difference between the two is Rs. 1,288.95.

    Compound Interest with Monthly Contributions

    Compounding interest on fixed deposits where you are allowed to make monthly contributions can get a little tricky. For the amount invested during the compounding period, interest will be generated for the initial investment amount + monthly contributions. These deposits are rare but are an extremely good investment with whopping returns.

    For example, Rs. 10,000 is the initial fixed deposit amount. The investor deposits Rs. 1,000 every month for 5 years. If the interest is compounded annually, then the interest will be as follows:

    Period Investment Breakdown Investment + Interest Accumulated Interest Earned Total Value of Deposit
    Year 1 10,000 + 12,000 22,000 1,100 23,100
    Year 2 10000 + (12000 x 2) + 1,100 35,100 1,755 36,855
    Year 3 10000 + (12000 x 3) + (1,100 +1,755) 48,855 2,442.75 51,297.75
    Year 4 10000 + (12000 x 4) + (1,100 +1,755 + 2,442.75 ) 63.297.75 3164.87 66,462.64
    Year 5 10000 + (12000 x 5) + (1,100 +1,755 + 2,442.75 + 3164.87 ) 78,461.75 3,923.13 82,385.77

    Through this table, we can see that the interest earned is accumulated every year and added to the principal amount. The total money contributed by the investor is Rs. 10,000 initially, followed by Rs. 1,000 every month or Rs. 12,000 every year. The investor made a total contribution of Rs. 10,000 + Rs. 60,000. At the end of 5 years, the value of his deposit is Rs. 82,385.77. The total compound interest earned is Rs. 12,385.77.

    The Benefit of Compound Interest

    Compound interest is your biggest friend when it comes to deposits and investments. Working in favor of investments, you stand to gain much more from the interest payable. But compound interest will be your worst enemy when it is calculated on your loan or other debt. You will end up paying significantly more interest on your loan. In terms of fixed deposits, compound interest is a great way of earning more on your investment. You earn much higher returns with compound interest on long term deposits. Compounding interest monthly, quarterly and half-yearly can spike your interest even higher. The benefits of compound interest can be listed as follows:

    • Reinvestment - The interest earned will be reinvested into the same deposit.
    • Higher value of the deposit - Compound interest leads to a higher value of the deposit. Upon maturity, your deposit will be more than a deposit with simple interest.
    • Long-term savings - Compound interest deposits encourage long-term savings as the return on investment is much higher after 10 years or more.
    • Increased Earnings - Options of compounding monthly, quarterly, and half-yearly increase the interest earned.

    Financial platforms where compound interest is applicable

    Compound interest is used for both debit and credit aspects of the financial world. Listed below are some of the investments and credit options that use compound interest.


    • Savings Accounts
    • Fixed Deposits
    • Recurring Deposits
    • Other Certificates of Deposits
    • Reinvested Dividend Stocks
    • Retirement Funds


    • Loans
    • Credit Cards
    • Mortgages

    When it is used in case of deposits and investments, we stand to benefit. On the other hand, when compound interest is charged on loans and debt, the banks and lenders stand to gain.

    Compound Interest Formula Reviews

    • Axis Bank Fixed Deposit
      "Services are good"
      0.5 5.0/5 "Blown Away!"
      I also bank with Axis Bank for the fixed deposit. The customer support and response is good. There are no hassles in the process. I could open this account online. The lock in period is for one year. The rate of interest they provide on my savings is also satisfactory.
      Was this review helpful? 2
      , pune
      Reviewed on Feb 15, 2019
    • SBI Fixed Deposit
      "Good service"
      0.5 4.0/5 "Great!"
      I have fixed deposit with SBI,As per the bank norms rate of interest is up to 6.88%. I opened the account through bank, There is no maturity period, like it is no fixed period, i can keep on deposit whenever i want and i take whenever i need it is unlimited, Their service is good.
      Was this review helpful? 2
      , bangalore
      Reviewed on Feb 14, 2019
    • SBI Fixed Deposit
      "Good saving for future"
      0.5 4.0/5 "Great!"
      SBI FD account is good, 2 months back I opened this account through offline, I have invested some amount its good, the interest rate is around 8% per annum. The customer support is very good . I can access account through online banking its fine.
      Was this review helpful? 3
      , bangalore
      Reviewed on Feb 09, 2019
    • ICICI Bank Fixed Deposit
      "Need to increase the interest rate"
      0.5 5.0/5 "Blown Away!"
      I do have a fixed deposit account with ICICI and it was taken recently. I have chosen ICICI because my salary and saving account was maintained with them. I am getting good response from the customer service. They are giving average interest rate. I do monthly deposit of less than 50K.
      Was this review helpful? 0
      , mumbai
      Reviewed on Feb 09, 2019
    • Kotak Fixed Deposit
      "Good features"
      0.5 5.0/5 "Blown Away!"
      Kotak Mahindra Bank is good in their customer services. I bank with them for the fixed deposit. I could open this account online. The lock in period is for one and half year. The rate of interest is really good. I could also close the account online.
      Was this review helpful? 1
      , hyderabad
      Reviewed on Feb 07, 2019
    • SBI Fixed Deposit
      "Safe and secured investment"
      0.5 5.0/5 "Blown Away!"
      Currently FD interest rate is around 6.5% for per annum. I deposited one time amount of Rs. 2 lakhs for one year, I have activated the service through online, I have netbanking option to track the details, before expiry if we withdraw the amount but there will be interest various applicable.
      Was this review helpful? 3
      , bangalore
      Reviewed on Feb 07, 2019
    • HDFC Bank Fixed Deposit
      0.5 4.5/5 "Excellent!"
      I have a fixed deposit with HDFC which was started 2 years back. I have chosen it mainly for the interest rate and also its convenient to open this account online also am a salary account holder. The locking period is 5 years. I never faced issues with the customer service. They need an improvement on interest rate because I think it could be better.
      Was this review helpful? 3
      , bangalore
      Reviewed on Feb 01, 2019
    • SBI Fixed Deposit
      "Good for savings"
      0.5 4.0/5 "Great!"
      I have fixed deposit with SBI, I deposited one time amount of Rs. 2 lakhs. As per the bank norms rate of interest is 11.50%, I opened the account through bank, on time they activated the fixed deposit. There is no proper coordination with the staff end.
      Was this review helpful? 7
      , hyderabad
      Reviewed on Feb 01, 2019
    • review Fixed Deposit
      "Need scope of improvement on the online tech"
      0.5 4.0/5 "Great!"
      I have FD account with Janakalyan Sahakari bank, the interest rate is quite good. We can invested the minimum amount from Rs. 20,000 to max amount. I have term of one year, I opened the FD through branch, but for the activation they taken 48 hours. To track the FD details I need to visit to the bank.
      Was this review helpful? 3
      , mumbai
      Reviewed on Jan 28, 2019
    • YES Bank Fixed Deposit
      "Excellent service"
      0.5 5.0/5 "Blown Away!"
      I have the fixed deposit account with the Yes bank and the interest rate they have given me is good, and i had started this investment a long time back. The interest rate with them has also been good. They have given me up to 8% approx it high compare to other bank, that is best part, and On line banking services are fine one too and am really happy with them, but maturity period was not expired.
      Was this review helpful? 5
      , mumbai
      Reviewed on Jan 26, 2019
    • Punjab National Bank Fixed Deposit
      "Easy online access"
      0.5 3.5/5 "Pretty good"
      I have opened Fixed deposit account through online in PNB, depend upon the customer I can chose the tenure period. The interest rate is okay for the fixed deposit and they don't have any charges for the pre matured withdrawal. I can track my deposits through online.
      Was this review helpful? 2
      , mumbai
      Reviewed on Jan 25, 2019
    • HDFC Bank Fixed Deposit
      "Good investment"
      0.5 5.0/5 "Blown Away!"
      I have invested in the fixed deposit for the amount of Rs. 1 lakh for 10 years, the interest rate is around 9% per annum. I went to the bank and opened the FD, there is no charges for pre matured withdrawal. The executive explained each benefits of the FD.
      Was this review helpful? 6
      , bangalore
      Reviewed on Jan 24, 2019
    • HDFC Bank Fixed Deposit
      "Good Investment plan"
      0.5 4.0/5 "Great!"
      I have taken Fixed deposit account from HDFC bank where am getting good benefits from them . There is no charges for the account . Where they are giving good rate of interest i have chosen long term investment plan.Overall am satisfied with the service and response .
      Was this review helpful? 5
      , ahmedabad
      Reviewed on Jan 23, 2019
    • SBI Fixed Deposit
      "Need quick service"
      0.5 2.0/5 "Expected more"
      I have invested Rs. 2 lakhs in SBI fixed deposit, the interest will be calculated 7.5% for per year. They don't have any fee for account maintenance. I went to the branch to open fixed deposit but they taken 2 days of time to activate because they collected lots of documents for FD account opening.
      Was this review helpful? 8
      , hyderabad
      Reviewed on Jan 21, 2019
    • SBI Fixed Deposit
      "Average service"
      0.5 3.0/5 "Satisfactory"
      I have invested the fixed deposit with State bank of India.the services which they had provided so far has been average.The interest rate with them has been good and the growth with the investment has also been good.maturity period going to get it will get mature will do renew of that deposit,there overall service is quite average.
      Was this review helpful? 3
      , bhubaneshwar
      Reviewed on Jan 21, 2019
    • Bank of Maharashtra Fixed Deposit
      0.5 5.0/5 "Blown Away!"
      I have a Fixed Deposit in Bank of Maharashtra because its near to my place but the interest rate is very low compared to Punjab Maharashtra Cooperative Bank. It was opened before one year and have deposited 6L. I think the rate of interest is 8.25%. The services are excellent, I would suggest them to increase the interest rate.
      Was this review helpful? 0
      , new delhi
      Reviewed on Jan 19, 2019
    • SBI Fixed Deposit
      "Good FD account"
      0.5 5.0/5 "Blown Away!"
      I have invested the fixed deposit with State bank of India. Since the branch is nearest by my home and they have given me a locker facility hence i have chosen the fixed deposit with SBI. Overall, I'm very much satisfied with the services with SBI.
      Was this review helpful? 5
      , hyderabad
      Reviewed on Jan 18, 2019
    • YES Bank Fixed Deposit
      "Fraud by Yes Bank"
      0.5 1.0/5 "Really Bad"
      Yes Bank has not credited Interest for my Fixed Deposit. On enquiring they gave me a story that the interest amount has been adjusted towards TDS. They have not provided credit entry for the interest and the debit entry for the TDS respectively.
      Was this review helpful? 5
      , bhopal
      Reviewed on Jan 11, 2019
    • ICICI Bank Fixed Deposit
      "Smart Investment"
      0.5 5.0/5 "Blown Away!"
      In ICICI fixed deposit interest rate is around 6.75% per annum, I opened the FD through online. I have invested Rs. 1 lakh they wont take any charges for the pre matured fixed interest. I believe the interest rate is good compared to the government bank.
      Was this review helpful? 3
      , yamuna nagar
      Reviewed on Jan 10, 2019
    • review Fixed Deposit
      "Very very worst bank"
      0.5 0.5/5 "Unacceptable"
      Really very very very worst bank, even don't open a account here. the are charging continously without any reason, really i am very upset and disappointed with this bank. Interest rate for loan is very high. workers of this bank also money motivated.
      Was this review helpful? 2
      , erode
      Reviewed on Jan 10, 2019
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