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What Is Compounding & the Importance of Time Period?

In this blog, you’ll get an understanding of the concept of Compounding, Time Period, Rate of Return & Rule of 72.

Introduction: The Marvel of Compounding

Amidst the vast landscape of finance, arguably, few concepts stand out, capturing universal acknowledgment for their undeniable power and transformative impact – and compounding is undoubtedly one of them. But what exactly is compounding? Frequently referred to as the ‘eighth wonder of the world’, compounding can transform modest savings into substantial sums over time seamlessly. Yet, it’s essential to explore time’s role in this financial marvel. With that in mind, let’s embark on a journey to delve into the enchanting realm of compounding, as well as unveil the pivotal importance of the time period in this remarkable phenomenon.

What is Compounding: The Eighth Wonder of the World

Compounding, in essence, is the process where an investment earns interest, which then earns interest on itself, leading to exponential growth. Imagine planting a tree. Initially, it’s just a small sapling, but it grows, branches out over time, and starts bearing fruit. Similarly, with compounding, your initial investment is the sapling, and the returns it generates are the fruits that further contribute to growth.

Example: If you invest $1,000 at a 10% annual interest rate, you’ll earn $100 in the first year. In the second year, you earn interest not just on the initial $1,000 but also on the $100 interest from the first year. This cycle continues, leading to exponential growth.

The Magic of Time: Why Duration Matters

Time is the fuel that powers the engine of compounding. The longer you allow your investments to compound, the more significant the growth. It’s not just about the amount you invest but how long you let it work for you.

Graphical Insight: If you were to plot the growth of a compounded investment on a graph, the curve would start relatively flat but would steepen dramatically as time progresses, showcasing the exponential growth.

The Rule of 72: A Quick Estimation Tool

Often touted as a financial marvel, the Rule of 72 stands out as a simple yet powerful tool investors frequently use. Primarily, it’s designed to estimate how long it will take for an investment to double, given a fixed annual rate of return. Consequently, by employing this rule, you only need to divide 72 by the annual rate of return simply. Consequently, you’ll obtain an approximation of the years required.

Example: For an investment with a 6% annual return, the investment would take roughly \(72 \div 6 = 12\) years to double.

While it’s a rough estimate, the Rule of 72 provides a quick snapshot, helping investors set expectations and plan accordingly.

The Early Bird Advantage: Starting Early in Investments

Starting your investment journey early can have profound effects on the end results, thanks to compounding. Even if you start with a smaller amount, the extended time frame can lead to substantial growth.

Scenario Comparison:

  • John starts investing at age 25, contributing $200 every month at a 7% annual return. By age 65, he would have invested $96,000.
  • Jane begins investing at age 35, contributing $400 every month at the same 7% annual return. By age 65, she would have invested $144,000.

Despite investing more money, Jane would have a smaller final amount than John because John allowed his investments to compound for a longer period.

Calculating the Compounding

Let’s go back to John:

  1. Initial Age: 25 years
  2. Monthly Contribution: $200
  3. Annual Return Rate: 7% or 0.07 (when expressed as a decimal)
  4. Compounding Frequency: Assuming it’s compounded annually

The formula for compound interest is:

\[ A = P(1 + \frac{r}{n})^{nt} \]


  • \( A \) is the future value of the investment/loan, including interest.
  • \( P \) is the principal investment amount (initial deposit or loan amount).
  • \( r \) is the annual interest rate (as a decimal).
  • \( n \) is the number of times interest is compounded per year.
  • \( t \) is the number of years the money is invested or borrowed for.

In this case, since the investment is compounded annually, \( n = 1 \).

However, since there’s a monthly contribution, we’ll need to adjust the formula to account for this. The future value of a series of monthly contributions can be calculated using the future value of an annuity formula:

\[ A = PMT \times \frac{(1 + r)^{nt} – 1}{r} \]


  • \( PMT \) is the monthly contribution.

Calculating Future Value

For each year, we’ll calculate the future value of the investment up to that point, including the contributions made during that year.

Let’s create a table that shows the growth of the investment for each year from age 25 to age 65 (a 40-year span). The table will have the following columns:

  1. Age
  2. Total Contribution for the Year
  3. Total Amount at the End of the Year (including interest)

Here’s a sample structure for the first few rows:

AgeTotal Contribution for the YearTotal Amount at the End of the Year

For the first few rows, let’s calculate the values for the “Total Amount at the End of the Year” column.

End-of-Year Calculations

In order to calculate the “Total Amount at the End of the Year” for each age, we’ll adeptly utilize the future value of an annuity formula to account for the contributions. This calculated value will then be seamlessly amalgamated with the compound interest that accrued on the total from the previous year. Through this methodical approach, we’ll acquire a comprehensive understanding of the growth dynamics for each age.

Let’s break it down step by step:

  1. For Age 25:
    • Total Contribution for the Year = $200 x 12 = $2,400
    • Interest on the contribution = $2,400 * 0.07 = $168
    • Total Amount at the End of the Year = $2,400 + $168 = $2,568
  2. For Age 26:
    • Total Contribution for the Year = $200 x 12 = $2,400
    • Previous Year’s Amount with Interest = $2,568 * 1.07 = $2,747.56
    • Total Amount at the End of the Year (including this year’s contribution) = $2,747.56 + $2,400 = $5,147.56
    • Interest on the total amount = $5,147.56 * 0.07 = $360.33
    • Total Amount at the End of the Year = $5,147.56 + $360.33 = $5,507.89
  3. For Age 27:
    • Total Contribution for the Year = $200 x 12 = $2,400
    • Previous Year’s Amount with Interest = $5,507.89 * 1.07 = $5,893.44
    • Total Amount at the End of the Year (including this year’s contribution) = $5,893.44 + $2,400 = $8,293.44
    • Interest on the total amount = $8,293.44 * 0.07 = $580.54
    • Total Amount at the End of the Year = $8,293.44 + $580.54 = $8,873.98

Here’s the table structure for the first few rows:

AgeTotal Contribution for the YearTotal Amount at the End of the Year

You get the idea, but to help here is a graph


Here’s the line graph illustrating the “Total Contribution for the Year” and the “Total Amount at the End of the Year” against “Age”.

The blue line represents the “Total Contribution for the Year”, and the green line represents the “Total Amount at the End of the Year”. As expected, the total amount at the end of the year grows at a faster rate than the yearly contributions, likely due to compound interest or investment returns.

Rate of Return: The Compounding Catalyst

The rate of return acts as a catalyst in the compounding process. A higher rate can significantly amplify the effects of compounding, leading to larger end sums.

Example: Consider two investments of $10,000 each. One yields a 5% annual return, while the other offers 8%. Over 20 years, with compounding, the first investment would grow to approximately $26,532, while the second would soar to $46,609. This stark difference underscores the importance of seeking favorable rates of return.

Real-world Success Stories

Often hailed as a financial genius, Warren Buffett, undoubtedly one of the most successful investors of all time, stands as a shining testament to the unparalleled power of compounding. Initially starting his investment journey in his formative years and then, by diligently maintaining a consistent high rate of return, Buffett’s wealth, over time, grew exponentially over the ensuing decades. His story emphasizes the importance of both time and a favorable rate of return in harnessing the full potential of compounding.

Conclusion: The Timeless Power of Compounding

Undoubtedly, compounding stands as a testament to the age-old adage, “Time is money.” Firstly, by delving into and understanding its intricate mechanics, and then, by strategically leveraging both time and a favorable rate of return, investors can, over time, witness their wealth grow exponentially.In the financial journey, it’s not just about sprinting but also about the marathon. So, as you chart your investment path, remember to harness the timeless power of compounding, letting time and interest work in tandem to build your financial empire.

Sagar Pujari
6 min read

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