Compound Interest Calculator

What this tool does

The Compound Interest Calculator grows a starting amount at any compounding frequency, including continuous, and can add a regular monthly contribution. It shows the future value, interest earned, effective annual rate and a year-by-year growth table.

Compound interest means interest is added to the balance and then earns interest itself. Over long periods this snowball effect dominates: ₹1,00,000 at 8% compounded yearly becomes about ₹2,15,892 in 10 years, while simple interest at the same rate gives only ₹1,80,000. How often interest is credited also matters, because more frequent compounding lifts the effective yield slightly.

This calculator applies A = P × (1 + r/n)^(n·t) for a chosen frequency n, or A = P × e^(r·t) for continuous compounding. Monthly contributions are treated as end-of-month deposits that grow at the equivalent monthly rate, so you can model a savings plan on top of a lump sum. Everything is calculated in your browser.

How to use Compound Interest Calculator

1. Pick the currency for formatting.
2. Enter the principal (initial amount); it can be zero if you only make monthly contributions.
3. Enter the annual interest rate and the time period in years (decimals such as 2.5 are allowed).
4. Choose the compounding frequency, from yearly to continuous.
5. Optionally add a monthly contribution.
6. Read the future value and effective annual rate, then check the stacked chart and the year-wise table, which you can download as CSV.

Tips for better results

• Compare products using the effective annual rate (EAR): 7.9% compounded quarterly yields 8.14% a year, more than 8.1% compounded yearly.
• Use the rule of 72 as a sanity check: divide 72 by the rate to estimate the years needed to double, about 9 years at 8%.
• Time matters more than frequency; starting five years earlier usually adds far more than switching from yearly to monthly compounding.
• Enter a negative rate to see how a loss or a fee drag compounds over time.

Common use cases

• Estimating the future value of savings or a deposit at a known rate.
• Showing students how compounding frequency changes the final amount.
• Comparing two deposit offers quoted with different compounding periods.
• Projecting a lump sum plus regular monthly additions towards a goal.

Common mistakes to avoid

• Mixing up the nominal rate and the effective rate when comparing accounts.
• Expecting market investments to compound at a fixed rate every year; real returns fluctuate.
• Ignoring tax on interest, which lowers the rate that actually compounds.