Compound Interest Calculator
Find out how much your money will grow when interest earns interest. Enter your starting amount, annual rate, time period and how often interest compounds — you'll see the final amount and total interest earned instantly.
How to use this calculator
- Enter your principal — the amount you invest or deposit today.
- Enter the annual interest rate as a percentage (e.g. 8 for 8%).
- Enter the time period in years (use 0.5 for 6 months).
- Choose how often interest compounds — monthly is most common for savings and deposits — then press Calculate.
Formula used
Where A is the maturity amount, P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the time in years. Compound interest earned = A − P.
Example calculation
Invest 100,000 at 8% per year, compounded monthly, for 10 years:
A = 100,000 × (1 + 0.08/12)120 = 221,964. Total compound interest = 221,964 − 100,000 = 121,964 — more than doubling your money without adding another rupee, dollar or euro.
What is compound interest?
Compound interest is interest calculated on both your original principal and the interest already earned. Unlike simple interest, where you earn on the principal only, compounding means each period's interest joins the base for the next period — which is why growth accelerates over time.
The compounding frequency matters: the same 8% annual rate produces slightly more when compounded monthly than yearly, because interest is added to the base twelve times a year instead of once. Over long periods this snowball effect is powerful, which is why starting early is the single biggest advantage in long-term investing.
Why use this calculator?
- Compare how different rates, durations and compounding frequencies change your final amount before you commit money.
- See the real growth of fixed deposits, savings accounts, bonds and reinvested returns.
- Understand the true cost of compound-interest debt, like credit card balances, by running the same math in reverse.
Frequently asked questions
How do I calculate compound interest monthly?
Use the formula A = P(1 + r/12)^(12×t): divide the annual rate by 12, multiply the years by 12, and raise (1 + monthly rate) to that power. Or simply select "Monthly" in the calculator above and it does this for you.
What is the difference between simple and compound interest?
Simple interest is always calculated on the original principal only, so it grows in a straight line. Compound interest is calculated on principal plus accumulated interest, so it grows exponentially. Over 10 years at 8%, 100,000 earns 80,000 with simple interest but about 121,964 with monthly compounding.
Does more frequent compounding always mean more money?
Yes, but with diminishing returns. Moving from yearly to monthly compounding makes a noticeable difference; moving from monthly to daily adds very little. The rate and the time period matter far more than the frequency.
What is the Rule of 72?
A quick mental shortcut: divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 8%, money doubles in roughly 72 ÷ 8 = 9 years.
Can I use this calculator for any currency?
Yes. The compound interest formula is currency-independent — enter amounts in dollars, euros, rupees, pounds or any currency and the result is in the same currency.