Compound interest is the eighth wonder of the world — it is interest earned on interest. Unlike simple interest, which only grows the principal, compounding accelerates growth exponentially. The compounding frequency matters: money compounded monthly grows faster than money compounded annually at the same rate. This calculator shows you the exact impact of compounding frequency on your investment.
Compound Interest Formula
A = P × (1 + r/n)^(n×t), where P is the principal, r is the annual interest rate (as a decimal), n is the number of compounding periods per year, and t is the time in years. The more frequent the compounding (higher n), the greater the final amount. This is why monthly compounding (n=12) always produces a higher maturity value than annual compounding (n=1) at the same nominal rate.
Effective Annual Rate (EAR) vs Nominal Rate
The nominal rate is the stated interest rate. The Effective Annual Rate (EAR) accounts for compounding frequency: EAR = (1 + r/n)^n − 1. For example, a 10% nominal rate compounded monthly gives an EAR of 10.47%. When comparing investment products, always compare EARs — not nominal rates — for an apples-to-apples comparison.
The Rule of 72
A quick mental math trick: divide 72 by your annual return to estimate how many years it takes to double your money. At 8%, your money doubles in ~9 years. At 12%, it doubles in ~6 years. At 6%, it takes 12 years. The Rule of 72 illustrates why even a 2% difference in return dramatically changes long-term wealth creation.
Frequently Asked Questions
Which compounding frequency is best?
Higher frequency is always better for the investor (more frequent compounding = more interest). Most bank FDs compound quarterly. Mutual fund NAVs effectively compound daily as markets move. Savings accounts typically compound monthly or quarterly.
What is the difference between compound and simple interest?
Simple interest = Principal × Rate × Time. Compound interest earns interest on both the principal and accumulated interest. For short periods (< 1 year), the difference is small. Over long periods, compound interest grows dramatically faster.
Does EPF use compound interest?
Yes. EPF interest is calculated monthly on the running balance and credited annually. The effective compounding is monthly-to-annual, which is why EPF builds a significant corpus over 30+ years of contributions.