Compound Interest Calculator
See exactly how your money grows with the power of compound interest.
What is it?
Compound interest is the process by which interest is earned not only on the original principal but also on the accumulated interest from previous periods. Albert Einstein reportedly called it the "eighth wonder of the world" — and for good reason. Over long periods, compound interest can turn modest savings into substantial wealth, or turn a manageable debt into an overwhelming one. This free compound interest calculator shows you the future value of any investment or loan, given an initial amount (principal), an annual interest rate, a compounding frequency, and a time horizon. You can also add a regular contribution — monthly or annual deposits — to model a savings plan or retirement account. The calculator handles all standard compounding frequencies: daily (365×/year), weekly (52×/year), monthly (12×/year), quarterly (4×/year), semi-annually (2×/year), and annually (1×/year). More frequent compounding slightly increases the effective annual rate, which is why a "6% annual rate compounded daily" actually yields a little more than a "6% annual rate compounded annually." The tool shows both the nominal rate you enter and the effective annual rate (EAR) so you can compare offers accurately.
How to use it
- Enter your starting amount (principal) — this is the initial deposit or loan balance.
- Enter the annual interest rate as a percentage.
- Choose the compounding frequency: daily, monthly, quarterly or annually.
- Set the time period in years.
- Optionally, add a regular contribution (monthly or annual) to model ongoing deposits.
- The result shows total value, total interest earned, and a year-by-year growth breakdown.
Why use this tool
Understanding compound interest is one of the most important financial skills anyone can develop. This calculator makes the math transparent and intuitive — you can instantly see how changing the interest rate, time horizon, or contribution amount affects the final result. The interactive year-by-year table and growth chart reveal something that surprises many people: the growth is slow at first, then accelerates dramatically in later years. This is the "compounding curve" — and it explains why starting to save early, even with small amounts, matters so much. A 25-year-old who saves $200/month at 7% will retire with far more than a 35-year-old saving $400/month at the same rate. The tool also works for loans and credit cards — enter a debt balance and the interest rate to see how much you will owe in five years if you make no payments. Everything runs privately in your browser, with no data sent to any server.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus any interest already earned. Over time, this difference is enormous — a $10,000 investment at 5% for 30 years earns $15,000 in simple interest but over $33,000 in compound interest.
How does compounding frequency affect the result?
More frequent compounding means interest is applied to a growing balance more often, resulting in slightly more growth. Daily compounding at 6% per year produces an effective annual rate of about 6.18%, compared to 6.00% for annual compounding. The difference is small over short periods but significant over decades.
What is the Rule of 72?
The Rule of 72 is a quick mental shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6%, your money doubles in about 12 years (72 ÷ 6 = 12). At 9%, it doubles in roughly 8 years.
Can I use this for loan calculations?
This calculator shows how a balance grows with compound interest — useful for understanding credit card debt, payday loans, or any interest-bearing balance. For mortgage and loan repayment schedules with regular payments reducing the balance, use our Mortgage Calculator instead.
What is the effective annual rate (EAR)?
The EAR is the actual return you earn in a year when compounding is taken into account, as opposed to the stated nominal rate. For example, a 6% nominal rate compounded monthly has an EAR of about 6.17%. Comparing EARs lets you accurately compare investment or loan offers with different compounding frequencies.