What is compound interest?
Compound interest is the interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, where interest is earned only on the original amount, compounding allows your investment to grow at an accelerating rate over time. The longer you stay invested, the more powerful this effect becomes.
In India, compound interest is the foundation of most long-term investment products — from PPF and EPF to mutual funds and fixed deposits. Understanding how compounding works is the single most important step toward building long-term wealth. Even small, regular investments can grow into substantial sums given enough time and a reasonable rate of return.
How can this compound interest calculator help you?
This calculator is designed to show you the real power of compounding. Here is how it helps:
The compound interest formula
Compound interest is calculated using the following formula:
A = P x (1 + r/n)^(n x t)
In the formula the letters represent:
| Variable | Meaning |
|---|---|
| A | The maturity amount (principal + interest) |
| P | The initial principal (your original investment) |
| r | The annual interest rate (in decimal form, e.g., 10% = 0.10) |
| n | Number of times interest compounds per year |
| t | The total time the money is invested (in years) |
Example of compounding
Suppose you invest ₹1,00,000 at 10% per annum for 10 years. With yearly compounding, the maturity amount would be approximately ₹2,59,374. With monthly compounding, it rises to about ₹2,70,704. The difference of over ₹11,000 comes purely from the more frequent compounding.
A = 1,00,000 x (1 + 0.10/12)^(12 x 10) = ₹2,70,704
The total interest earned is ₹1,70,704, of which ₹1,00,000 came from compounding on the original principal and ₹70,704 came from interest earned on previously accumulated interest.
Factors that affect your compound returns
Principal Amount
The larger your initial investment, the larger the base on which compounding works. Even a modest increase in the principal can lead to a significantly larger corpus over long periods.
Rate of Return
The interest rate is the most powerful lever. A difference of just 1% per annum can translate to lakhs of rupees difference over 20-30 years. This is why equity investments, which have historically returned 10-12% over long periods, are preferred for long-term goals like retirement.
Time Horizon
Time is the most critical factor. The earlier you start investing, the more powerful the compounding effect. An investor who starts at age 25 and invests for 10 years will likely end up with more than someone who starts at age 35 and invests for 20 years, thanks to the extra decade of compounding.
Compounding Frequency
More frequent compounding means your money grows faster. Monthly compounding yields slightly more than quarterly, which yields more than yearly. Use the frequency selector in the calculator to see the exact difference for your numbers.
Compound interest in popular Indian investments
PPF (Public Provident Fund)
PPF compounds annually and currently offers around 7-8% interest. The 15-year lock-in period makes it a good vehicle for long-term compounding. Interest earned is tax-free under Section 80C.
EPF (Employees\' Provident Fund)
EPF compounds at a rate declared annually by the government (currently around 8-8.5%). Both employer and employee contributions compound over the service period, creating a substantial retirement corpus.
Fixed Deposits
Most banks compound interest on fixed deposits quarterly or half-yearly. Senior citizens get slightly higher rates. The compounding frequency and tenure affect the effective yield.
Mutual Funds & Equity
Mutual funds and equity investments grow through capital appreciation and dividend reinvestment. While returns are not guaranteed, the long-term compounding effect of 10-12% annualised returns over 20-30 years is remarkable.
How to use this calculator
Using the compound interest calculator is simple:
The maturity amount, total interest earned, and effective annual rate are calculated instantly. The year-wise growth schedule shows exactly how your investment builds over time.