Compound Interest Calculator
A compound interest calculator shows you how your money grows when interest is added back to the principal at regular intervals, so that you earn interest on your interest. This is what Albert Einstein reportedly called the eighth wonder of the world, and it is the single most powerful force in long-term investing. Unlike simple interest, which only pays interest on the original amount, compound interest pays interest on the original amount plus all the interest that has accumulated so far. The more frequently the interest is compounded, the faster your money grows. This calculator takes four inputs: the principal amount you start with, the annual interest rate, the time period in years, and the compounding frequency (annually, semi-annually, quarterly, monthly, or daily). It then shows the total amount you will have at the end and the total interest earned. Compound interest is the foundation of long-term wealth building. Whether you are investing in fixed deposits, bonds, or mutual funds, understanding how compounding works helps you make smarter financial decisions and see why starting early matters so much.
Formula
A = P x (1 + r/n)^(n x t) Where: A = Final amount (principal + interest) P = Principal (initial investment) r = Annual interest rate (as a decimal, e.g. 8% = 0.08) n = Compounding frequency per year t = Time in years
Example
Example: Invest Rs 1,00,000 at 8% annual interest for 5 years, compounded monthly. Step 1: Identify the values P = 1,00,000 r = 8 / 100 = 0.08 n = 12 (monthly compounding) t = 5 years Step 2: Apply the formula A = 1,00,000 x (1 + 0.08/12)^(12x5) A = 1,00,000 x (1.00667)^60 A = Rs 1,48,985 (approx) Step 3: Interest earned = 1,48,985 - 1,00,000 = Rs 48,985 Result: Your Rs 1 lakh grows to about Rs 1.49 lakh in 5 years. With simple interest you would have earned only Rs 40,000, so compounding adds an extra Rs 8,985.
How to Use
- Enter the principal amount you want to invest.
- Enter the annual interest rate as a percentage.
- Enter the time period in years.
- Select the compounding frequency (annually, monthly, daily, etc.).
- Click Calculate to see the final amount and total interest earned.
Frequently Asked Questions
What is compound interest?
Compound interest is interest calculated on the initial principal plus all the accumulated interest from previous periods. In other words, you earn interest on your interest. This causes your money to grow at an accelerating rate over time, which is why compound interest is so powerful for long-term investing.
How is compound interest different from simple interest?
Simple interest is calculated only on the original principal amount, so the interest earned is the same every year. Compound interest is calculated on the principal plus accumulated interest, so the interest earned grows larger each year. Over long periods, compound interest produces significantly higher returns than simple interest.
What is the best compounding frequency?
More frequent compounding produces slightly higher returns. Daily compounding earns more than monthly, which earns more than quarterly, which earns more than annual. However, the difference is small for moderate rates. For example, at 8% annual interest over 5 years, daily compounding earns only about 0.1% more than monthly compounding.
Does the Rule of 72 work for compound interest?
Yes. The Rule of 72 is a quick way to estimate how long it takes for an investment to double at a given compound interest rate. Divide 72 by the annual interest rate to get the approximate number of years. For example, at 8% annual interest, your money doubles in about 72 / 8 = 9 years.
What is continuous compounding?
Continuous compounding is the theoretical limit of compounding frequency, where interest is compounded infinitely often. The formula becomes A = P x e^(r x t), where e is Euler's number (approximately 2.71828). In practice, daily compounding is very close to continuous compounding.
Why does starting early matter so much with compound interest?
Because compound interest grows exponentially, time is the most important factor. Someone who invests Rs 5,000 per month from age 25 to 35 (10 years) and then stops will often have more money at age 60 than someone who invests Rs 5,000 per month from age 35 to 60 (25 years), because the early investor's money has 25 extra years to compound.