Compound Interest Calculator
See how a one-time principal grows under compound interest at any rate, tenure, and compounding frequency (daily, monthly, quarterly, yearly).
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Start with the formula
A = P(1 + r/n)^(nt). That one line drives almost every saving and investment product you'll ever use. P is what you start with, r is the annual rate as a decimal, n is how many times a year the interest compounds, and t is the number of years. The output A is what you end up with. Once you see how those four levers move the result, a lot of financial advice suddenly makes sense.
Compound versus simple, and why it matters
Simple interest only ever pays on your original principal. Park Rs 50,000 at simple interest and the interest each year stays flat. Compound interest is different. It pays on your principal plus all the interest already earned, so the base keeps growing. Year after year the gap widens. Over a decade or two, compound interest pulls so far ahead that it doesn't even look like the same starting amount.
Frequency adds a smaller second boost. The bigger n is, the more often interest folds back in, and the slightly higher your return. Annual compounding is fine. Quarterly is a touch better. Monthly, better still. The differences are modest, but they're real, and over long periods they're worth grabbing.
A worked case makes it concrete. A Hyderabad investor puts Rs 2,00,000 at 8 percent compounded annually for 10 years. Run A = 2,00,000 times (1.08)^10, and the money grows to about Rs 4,31,785. So Rs 2,31,785 earned on a single deposit, just by leaving it alone and letting each year build on the last.
A shortcut for doubling
There's a handy trick called the Rule of 72. Divide 72 by your annual rate and you get the rough number of years for your money to double. At 8 percent, that's 72 divided by 8, so about 9 years. At 12 percent, roughly 6 years. It's not exact, but it's close enough to do in your head, and it tells you something powerful. Rate and time, not luck, are what move the needle. Start early. Let it run. The math takes over.
Compound Interest Calculator — frequently asked questions
What is the compound interest formula?
The formula is A = P times (1 + r/n) raised to the power (n times t). Here P is the principal, r is the yearly rate as a decimal, n is how many times interest compounds per year, and t is the number of years. A is the final amount including interest. To find just the interest, subtract P from A. It works for FDs, loans, and most investments.
How is compound interest different from simple interest?
Simple interest is always calculated only on the original principal, so the yearly interest stays the same. Compound interest is calculated on the principal plus all the interest already earned, so the base keeps growing each period. Over a year or two the gap is small, but over ten or twenty years compound interest pulls far ahead and earns much more on the same starting amount.
Does compounding frequency really change my returns?
Yes, but the effect is modest. The more often interest compounds, the more often earned interest starts earning too, which lifts your final amount slightly. Monthly compounding beats quarterly, which beats annual, on the same rate. The difference grows with time and with larger sums. So between two equal-rate options, pick the one that compounds more often, but do not expect a dramatic jump from frequency alone.
What is the Rule of 72?
It is a quick mental shortcut to estimate how long money takes to double. Divide 72 by your annual interest rate, and the answer is roughly the number of years needed. At 9 percent, 72 divided by 9 gives about 8 years. It is not perfectly exact, but it is close enough for rough planning and helps you compare how rate affects doubling time without a calculator.
Why does starting early matter so much in compounding?
Because compound growth builds on itself, the extra years at the start are the most powerful ones. Money invested early has more time to earn interest on interest, and that snowball gets bigger near the end. Someone who starts at 25 can end up far ahead of someone who starts at 35 with the same monthly amount, simply because of those extra compounding years.
Can I use this formula for both savings and loans?
Yes, the same compound interest formula applies to both. On savings and FDs it shows how your money grows over time. On loans and credit cards it shows how much you owe as interest piles onto the balance. The maths is identical, only the direction differs. Understanding it helps you grow savings faster and avoid the trap of compounding debt working against you.
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Results from this calculator are estimates for informational use only — not financial, medical, or professional advice. Read our full disclaimer before acting on any number you see here.