Compound Interest Calculator
Compound interest is interest earned on both your original amount and the interest already added — it is why savings and investments grow faster over time. This calculator shows the future value of a lump sum, the total interest earned, and how often your money doubles, for any currency.
- Principal
- Interest
- Starting amount
- $10,000.00
- Interest earned
- $12,196.40
- Total growth
- 121.96%
At 8% compounded monthly, your money doubles roughly every 8.7 years. Over 10 years it grows to 2.22× your starting amount.
Ways to optimize
Real what-if scenarios calculated from your numbers.
Scenarios use the exact same math as the calculator — no estimates.
Returns must exceed ~7% inflation to grow real purchasing power
What this calculator tells you
Surfaces the exact doubling time and final growth multiple, plus the nominal-vs-effective rate caveat — turning a commodity formula into actionable insight.
Frequently asked questions
What is the difference between simple and compound interest?+
Simple interest is calculated only on your original amount. Compound interest is calculated on the original amount plus all previously earned interest, so it grows faster over time.
Does compounding frequency really matter?+
Yes, but with diminishing returns. Monthly compounding beats annual, and daily beats monthly, but the gap shrinks as frequency rises. The rate and the time horizon matter much more.
How long until my money doubles?+
The calculator shows the exact doubling time for your rate. As a quick estimate, the rule of 72 says years-to-double ≈ 72 ÷ interest rate.
Can I use this for any currency?+
Yes — the math is identical everywhere. Use the currency switcher at the top of the page.
How does compound interest work in Indian fixed deposits?+
Most Indian bank FDs compound interest quarterly, even if the payout is monthly or at maturity. The interest rate advertised is the nominal annual rate; the effective annual yield (EAR) is slightly higher due to quarterly compounding. TDS of 10% is deducted on FD interest above ₹40,000 per year (₹50,000 for senior citizens) under Section 194A, which reduces your net compounded return.
What is the difference between nominal rate and effective annual rate (EAR)?+
The nominal rate is the stated annual rate before compounding frequency is applied. The effective annual rate (EAR) is the actual annual return after accounting for compounding: EAR = (1 + r/m)^m − 1, where m is the number of compounding periods per year. A 12% nominal rate compounded monthly has an EAR of about 12.68%, making it meaningfully higher than a 12% rate compounded annually.
Compound interest vs SIP — which grows wealth faster?+
A lump sum earning compound interest and a SIP both use compounding, but the mechanism differs. A lump sum compounds the full amount from day one, so it wins over a SIP of equivalent total contributions if markets stay flat and returns are constant. A SIP averages the entry price across market cycles, reducing timing risk — in volatile equity markets this often leads to better risk-adjusted outcomes for regular investors than putting a lump sum in at the wrong time.
Does the PPF account in India use compound interest?+
Yes. The Public Provident Fund (PPF) compounds annually at a rate set by the government each quarter (currently 7.1% as of 2025). Interest is calculated on the minimum balance between the 5th and the last day of each month, so depositing before the 5th of a month ensures that month's balance earns interest. The interest is tax-free under Section 10(11) of the Income Tax Act, making the effective post-tax yield attractive compared to FDs for those in higher tax brackets.
How it works
With compound interest, each period’s interest is added to the balance, so the next period earns interest on a larger amount. The more frequently interest compounds (daily versus annually), the faster it grows, though the difference narrows at higher frequencies. Time is the biggest lever: because growth is exponential, the final years add far more than the early ones.
The formula is currency-agnostic — switch the currency at the top to view your numbers in your own.
A = P · (1 + r/m)^(m·t), where P = starting amount, r = annual rate (as a decimal), m = compounding periods per year, and t = years. Interest earned = A − P.
Worked example
Put 10,000 in at 8% per year compounded monthly for 10 years. Using A = 10,000 · (1 + 0.08/12)^(12·10), the balance grows to about 22,196 — you earn roughly 12,196 in interest, more than doubling your money. At 8% compounded monthly, money doubles about every 8.7 years.
Edge cases & caveats
Continuous compounding (the theoretical limit) uses A = P · e^(r·t) and is only marginally higher than daily. Beware quotes that mix nominal and effective rates: a 12% rate compounded monthly has an effective annual rate of about 12.68%. For regular contributions rather than a single lump sum, use a SIP or investment calculator instead.
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Disclaimer: This calculator is for educational and informational purposes only and provides estimates, not financial advice. Interest rates, taxes, fees, and local rules vary and change over time. Confirm figures with a qualified professional before making any financial decision.
Last reviewed: 2026-06-22