Compound Interest Calculator
Estimate how your investment grows with compound interest.
What is it?
Compound interest is interest calculated on both the original principal and the interest already accumulated. Unlike simple interest, this creates exponential rather than linear growth — the more often interest compounds, the faster your money grows.
Formula
A = P × (1 + r/n)^(n × t)
- P = Principal amount
- r = Annual interest rate (as a decimal)
- n = Number of times interest compounds per year
- t = Time in years
Formula Explanation
Dividing the annual rate by the compounding frequency (n) gives the rate applied each period, and raising it to the power of total periods (n × t) captures how interest earns interest at every compounding step. More frequent compounding (monthly vs. yearly) results in a slightly higher final amount at the same nominal annual rate.
Example Calculation
$100,000 at 10% annual interest compounded yearly for 10 years grows to about $259,374. Compounded monthly instead, it grows slightly more, to about $270,704.
How to Use
- Enter the principal amount you plan to invest.
- Enter the annual interest rate.
- Enter the time period in years.
- Choose how often interest compounds (yearly or monthly).
- View the final amount and total interest earned.
Benefits
- Shows the exact impact of compounding frequency on your final returns.
- Illustrates why "interest on interest" accelerates growth over time.
- Useful for comparing fixed deposits, bonds, or savings accounts with different compounding terms.
Use Cases
- Comparing fixed deposit or savings account offers with different compounding frequencies.
- Understanding how a lumpsum grows under compound interest over time.
- Illustrating the long-term power of compounding for financial literacy.
What Your Result Means
The final amount is your principal plus all accumulated compound interest. The gap between principal and final amount grows disproportionately larger the longer the money stays invested, since later years compound on an already-larger base.
Tips
- More frequent compounding (monthly vs. yearly) results in modestly higher returns at the same nominal rate.
- The biggest gains from compounding come from time, not just rate — starting early matters most.
- Compare offers by their effective annual rate, not just the nominal rate, when compounding frequency differs.
Common Mistakes
- Confusing nominal interest rate with effective annual rate when compounding is more frequent than yearly.
- Assuming compound interest calculations account for taxes on interest income — they typically don't unless you adjust the rate.
- Underestimating how much compounding frequency and duration change the final result over long periods.
FAQs
Does compounding frequency really make a difference?
Yes. Monthly compounding grows your money faster than yearly compounding at the same nominal rate, since interest is added to the principal more often.
How is compound interest different from simple interest?
Simple interest is calculated only on the original principal, while compound interest is calculated on the principal plus all previously accumulated interest.
Why does starting early matter so much?
Compounding accelerates over time — money invested early has more compounding cycles to grow, often outperforming larger amounts invested later.
Is interest earned on a savings account taxable?
Generally yes, in most tax jurisdictions interest income is taxable — consult a tax professional for rules specific to your situation.
What compounding frequency do banks typically use?
It varies — savings accounts often compound quarterly or monthly, while fixed deposits may compound quarterly or annually depending on the bank and product.
This calculator provides estimates for informational purposes only. Actual returns depend on the specific investment or account terms.
Last updated: July 25, 2026