Compound Interest Calculator
Calculate how much your investment will grow over time with compound interest. Supports regular contributions, multiple currencies, and 11 compounding frequencies.
Enter your principal amount, interest rate, and duration to calculate interest earnings and visualize investment growth over time.
Click "Calculate" to view results.
Principal + Total Interest
Total interest earned
| Year | Deposits | Interest | Total Deposits | Total Interest | Balance |
|---|---|---|---|---|---|
Calculation Summary
Formula Used
Where P = principal, r = annual interest rate (as decimal), t = time in years, n = compounding frequency
What Is the Compound Interest Calculator?
The Compound Interest Calculator computes how an initial deposit (principal) grows over time when interest is periodically calculated on both the original principal and all previously accumulated interest. This "interest on interest" effect is what separates compound interest from simple interest and is the primary driver of long-term wealth accumulation.
Albert Einstein reportedly called compound interest "the eighth wonder of the world." Whether you're saving for retirement, evaluating a certificate of deposit (CD), or comparing high-yield savings accounts, understanding compound interest is essential for making informed financial decisions.
The Compound Interest Formula
A = P × (1 + r/n)^(n×t)
where P = principal, r = annual interest rate (decimal), n = compounding frequency per year, and t = time in years. The result A is the future value including all accumulated interest.
Compounding Frequencies Compared
- Annually (n=1): Interest calculated once per year — simplest but lowest effective yield.
- Monthly (n=12): Most common for savings accounts and CDs.
- Daily (n=365): Used by many high-yield savings accounts and money market funds.
- Continuously: Theoretical limit where compounding happens infinitely often, using the formula A = P × e^(r×t).
How to Use the Compound Interest Calculator
Using this calculator is straightforward. Enter your known values into the fields below, and the solver will compute the result immediately. Here is what each input represents:
Worked Example: 5-Year Monthly Compounding Savings Plan
Problem: You deposit $5,000 into a savings account earning 5% annual interest, compounded monthly (12 times per year), for 5 years. What is the future value and total interest earned?
1. Identify the Given Variables
Principal (P) = $5,000, Annual Rate (r) = 5% = 0.05, Compounds per year (n) = 12, Time (t) = 5 years.
2. Calculate the Periodic Interest Rate
Divide the annual rate by the number of compounding periods: 0.05 / 12 = 0.0041667 per month.
3. Compute Total Number of Periods
Multiply compounds per year by time: 12 × 5 = 60 total compounding periods.
4. Apply the Compound Interest Formula
A = $5,000 × (1 + 0.0041667)^60 = $5,000 × 1.283359 = $6,416.79.
How to Calculate Compound Interest Step-by-Step
Understanding the underlying solution workflow helps build mathematical intuition:
Real-World Applications of Compound Interest Calculator
Retirement Savings (401k, IRA, Pension)
Compound interest is the engine behind long-term retirement accounts. Starting early allows decades of compounding to turn modest monthly contributions into substantial nest eggs.
Certificate of Deposit (CD) Comparison
Banks offer CDs with different rates, terms, and compounding frequencies. This calculator lets you compare the actual dollar return across competing CD offers.
Student Loan & Credit Card Debt Analysis
Compound interest also works against borrowers. Understanding how credit card APRs compound monthly helps you see the true cost of carrying a balance.
Common Pitfalls & Mistakes to Avoid
Confusing APR with APY
APR (Annual Percentage Rate) does not account for compounding. APY (Annual Percentage Yield) does. A 5% APR compounded monthly yields an APY of approximately 5.116%. Always compare APY to APY.
Ignoring Inflation's Erosion of Real Returns
A 5% nominal return with 3% inflation yields only ~2% real purchasing power growth. Subtract inflation from your interest rate for a more realistic projection.
Forgetting Taxes on Interest Income
Interest income is typically taxed as ordinary income. Factor in your marginal tax rate when projecting net returns from savings accounts and CDs.
Key Terminology Glossary
Expert Tips for Compound Interest Calculator
- The frequency of compounding (e.g., daily, monthly, quarterly) determines how quickly interest accumulates; daily compounding yields the highest return, but the difference from monthly is usually small.
- Use the Rule of 72 to estimate how long it will take your investment to double: divide 72 by your annual interest rate. At 6%, your money doubles in roughly 12 years.
- Regular contributions (even small ones) can dramatically increase your final balance over long time periods — consistency matters more than the amount.
- Be mindful of the difference between nominal interest rate and annual percentage yield (APY), which accounts for compounding. APY is the 'real' rate you earn.
- Starting early is the most powerful factor in compound interest — 10 years of compounding beats a larger initial investment over 5 years in most cases.
About the Compound Interest Calculator
The Compound Interest Calculator is maintained by Basic Math Tools, an educational platform committed to providing accurate STEM and financial computing tools. Every tool processes calculations transparently in your browser for privacy and speed.
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