Compound Interest Calculator

Compound interest is the single most powerful force in personal finance. Understanding it completely changes how you think about saving, investing and debt.

The idea is simple. With simple interest, you earn interest only on your original principal. With compound interest, you earn interest on your principal plus all the interest you have previously earned. Your money makes money on the money it already made. This recursive growth creates exponential curves.

A Concrete Example

Two people — Priya starts investing ₹5,000 per month at age 25. Rahul waits until 35. Both invest until age 60 at 12% annual returns. Priya ends up with approximately ₹3.2 crore. Rahul ends up with approximately ₹1.7 crore. Priya invested for 10 more years and nearly doubled Rahul's wealth. Those 10 early years of compound growth make an enormous difference. This is why "start early" is the most repeated and most ignored financial advice.

Compounding Frequency

More frequent compounding always means higher returns. Annual compounding calculates interest once per year. Monthly calculates 12 times. Daily calculates 365 times. For a ₹1 lakh investment at 10% over 10 years — annual compounding gives ₹2.59 lakhs, monthly gives ₹2.71 lakhs. The ₹12,000 difference matters at scale.

Compound Interest Works Both Ways

This is the part people ignore about credit card debt. A credit card charging 42% annual interest on ₹50,000 — paying only minimums for 3 years — could leave you owing over ₹1.5 lakhs. High-interest debt is the mathematical inverse of compound investment. Pay it off before investing.

The Rule of 72

Divide 72 by the annual interest rate to estimate years to double your money. At 8%, 72 ÷ 8 = 9 years to double. At 12%, 72 ÷ 12 = 6 years. Quick mental math for comparing investment options.