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.
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.
Things to watch out for
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.
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.
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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