Compound Interest Calculator
See how your money grows with compound interest.
How to Use Compound Interest Calculator
- 1Enter the principal amount
- 2Enter the annual interest rate
- 3Choose the compounding frequency
- 4Enter the investment period in years
- 5Click Calculate to see growth
About Compound Interest Calculator
Compound interest is one of the most powerful forces in personal finance: it is the interest earned on both the original principal and the interest that has already accumulated. This calculator uses the formula A = P(1 + r/n)^(nt) to show how your investment grows over time.
Choose from five compounding frequencies — daily, weekly, monthly, quarterly, or annually — to see how often interest is added to the principal. The tool also shows the comparison against simple interest so you can see exactly how much extra you earn through compounding.
All processing runs in your browser with no server communication, making it ideal for modeling investment scenarios, savings goals, and loan costs privately. The results include final balance, total interest earned, and an effective annual rate (EAR).
Key Features of Compound Interest Calculator
- Compound interest formula: A = P(1 + r/n)^(nt)
- Choose from daily, weekly, monthly, quarterly, or annual compounding
- Shows final balance, total interest, and effective annual rate
- Compares result against simple interest for the same inputs
- Works with any principal and any positive interest rate
- Time period input in years with support for fractional years
- Instant calculation with no page reload
- Useful for investment projections, savings modeling, and loan analysis
Examples
Investment growth with monthly compounding
Calculate how $10,000 grows over 10 years at 5% compounded monthly.
Input
Principal: 10000, Rate: 5%, Time: 10 years, Monthly compounding
Output
Final balance: $16,470.09 | Interest earned: $6,470.09
Compare compounding frequencies
See how daily compounding beats annual compounding for the same inputs.
Input
Principal: 1000, Rate: 10%, Time: 5 years
Output
Annual: $1,610.51 | Monthly: $1,645.31 | Daily: $1,648.61
Common Use Cases
- Projecting long-term investment growth in a savings account
- Modeling retirement savings with different interest rate assumptions
- Comparing savings accounts with different compounding frequencies
- Understanding how quickly debt grows when interest compounds
- Teaching students the concept of exponential financial growth
- Estimating the future value of a lump-sum investment
Troubleshooting
Entering the annual rate as a decimal
Solution
Enter the rate as a percentage. For a 5% annual rate, enter 5, not 0.05. The calculator handles the conversion internally.
Expecting daily and monthly compounding to give very different results
Solution
The difference between daily and monthly compounding is very small in practice. For a $10,000 investment at 5% over 10 years, monthly compounding gives $16,470 while daily gives $16,487 — a difference of only $17.
Confusing nominal rate with effective annual rate
Solution
The nominal rate is the stated annual rate. The effective annual rate (EAR) is higher when compounding is more frequent than annual. The calculator shows the EAR so you can compare products with different compounding schedules.
Frequently Asked Questions
What is compound interest?
Compound interest means interest is calculated on the accumulated balance (principal plus previous interest), not just on the original principal. This causes the balance to grow exponentially over time.
What is the compound interest formula?
A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal, n is compounding periods per year, and t is time in years.
Which compounding frequency gives the most interest?
More frequent compounding gives more interest, with daily compounding being the maximum in practice. However, the difference between daily and monthly compounding is very small for typical interest rates.
What is the effective annual rate (EAR)?
The EAR is the actual annual return accounting for compounding frequency. For a 12% nominal rate compounded monthly, the EAR is approximately 12.68%. It lets you compare products with different compounding schedules on equal terms.
How does compound interest compare to simple interest?
For the same principal and rate, compound interest always produces a higher total than simple interest over more than one compounding period. The gap widens significantly over long time horizons.
Does this calculator include additional contributions?
No, this calculator models a single lump-sum investment. For regular monthly contributions, use the Savings Calculator which handles both initial deposits and ongoing contributions.
Can I model debt growth using this calculator?
Yes. Enter your outstanding debt balance as the principal and your annual interest rate. The result shows how much the balance will grow if no payments are made, illustrating why compound interest on debt is dangerous.
Is my data private?
Yes. All calculations run entirely in your browser. No financial data is transmitted to any server.