See exactly how your money grows over time with principal, regular contributions, and the power of compounding — with interactive charts and a full year-by-year growth schedule.
Results update live as you type.
Final Balance
Starting Amount
$10,000
initial investment
Total Contributions
$48,000
over 20 years
Interest Earned
$0
compound growth
Total Return
0%
on total invested
| Year | Contributions | Interest | Balance |
|---|
The Formula
The calculator applies the standard compound interest formula to your principal and then compounds each monthly contribution individually from the date it is made. The result is your true projected balance — not an approximation.
With regular contributions, each deposit earns interest for the remaining time in the period. The more frequent the compounding, the slightly higher the final balance — though the rate and time horizon are far more impactful than compounding frequency.
Formula
About This Tool
A compound interest calculator — sometimes called an investment growth calculator or savings growth calculator — is a free online tool that instantly shows how money grows when earnings are reinvested. Unlike simple interest, where only the original principal earns interest, compound interest earns interest on interest, creating exponential growth over time.
Our calculator handles both lump-sum investments and regular monthly contributions. Enter your starting amount, annual return rate, investment horizon, monthly deposits, and how often interest compounds — and the tool shows your projected final balance, total interest earned, and a full year-by-year growth schedule in real time.
Whether you're planning for retirement, building an emergency fund, growing a stock portfolio, or evaluating a savings account, this free compound interest calculator gives you an accurate picture of where consistent saving and smart investing can take you. All calculations happen in your browser — no sign-up required.
Albert Einstein reportedly called compound interest the "eighth wonder of the world." Start the calculator today and see why: even modest monthly contributions, given enough time and a reasonable rate, can grow into extraordinary wealth.
Live Growth Projection
Balance updates in real time as you adjust any input — no button needed.
Contribution Modelling
Includes regular monthly deposits on top of your initial principal.
Year-by-Year Schedule
Annual breakdown of contributions, interest, and balance for every year.
100% Free & Private
No account needed. All calculations run locally in your browser.
4 Compounding Options
Compare annual, quarterly, monthly, and daily compounding in one click.
Interactive Charts
Visualise growth over time and see the breakdown of principal vs. interest.
Five simple inputs reveal exactly how your money grows — including contributions and compounding frequency.
Type the lump sum you're starting with, or drag the slider to explore different starting amounts. This is your principal — the foundation on which all future compounding is built.
Enter the annual percentage yield (APY) for your investment or savings account. Use a conservative rate for planning — the long-term stock market average is roughly 7% after inflation. Even small changes in rate have a massive impact over time.
Drag the slider or type in the number of years you plan to invest. Time is the most powerful variable in compound interest — doubling your investment period can more than quadruple your final balance at the same rate.
Enter how much you plan to add each month. Regular contributions often matter more than the starting amount over long periods — $200/month at 7% for 30 years grows to over $230k in contributions alone.
Choose how often interest compounds — Annual, Quarterly, Monthly, or Daily. More frequent compounding yields slightly more. Tap each option to compare. Then review the charts and schedule to see your full growth picture.
Everything you need to know about compound interest, how to use this calculator, and how to grow your money smarter.
Compound interest is interest calculated on both the initial principal and all previously accumulated interest. Unlike simple interest (which only applies to the original principal), compounding causes balances to grow exponentially. A $10,000 investment at 7% earns $700 in year one — but in year two it earns interest on $10,700, producing $749. This "interest on interest" effect accelerates over time and is the fundamental engine behind long-term wealth building. Our compound interest calculator shows this growth year by year so you can see the compounding curve first-hand.
The standard formula is A = P(1 + r/n)^(nt), where P is your principal, r is the annual interest rate as a decimal, n is how many times per year interest compounds, and t is the number of years. When you also make regular monthly contributions (PMT), each deposit is compounded from the date it is made using a future-value-of-annuity formula layered on top. Our compound interest calculator handles both parts simultaneously so your results reflect the full picture — not just a lump sum estimate.
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%, money doubles in about 12 years; at 8%, roughly 9 years; at 4%, around 18 years. The rule works because 72 ÷ r ≈ ln(2) / ln(1+r) for rates between 1% and 20%. It is useful for comparing investment accounts, retirement projections, and debt scenarios without a calculator. Use our compound interest growth calculator for precise figures across any time horizon.
More frequent compounding produces slightly higher returns because interest is added to the balance more often — giving each increment a longer time to earn more interest. Going from annual to monthly compounding on $10,000 at 7% over 20 years adds approximately $1,400 to the final balance. Going from monthly to daily adds only about $50 more. In practice, the difference between monthly and daily compounding is negligible. What matters far more is your interest rate and how long you stay invested. Use the frequency toggle in our calculator to compare each option instantly.
Regular contributions dramatically amplify the compounding effect because each new deposit starts earning interest immediately. A $200/month contribution at 7% for 30 years generates roughly $228,000 in cumulative contributions — which, with compounding, grows to over $243,000 in interest alone. The habit of consistent saving is arguably more important than starting with a large lump sum. Many people successfully build retirement portfolios entirely through monthly contributions without a significant initial investment. Use the monthly contribution slider in our calculator to see the impact of adding — or increasing — your deposits.
Use the actual APY (Annual Percentage Yield) for your specific account or investment. Common benchmarks: HYSA / money market accounts: 4–5% (as of 2024–2025); US stock market (S&P 500): ~10% nominal, ~7% real (inflation-adjusted) long-term average; bonds / fixed income: 3–5%; savings accounts: 0.5–2%. For long-term retirement projections, many financial planners recommend using 6–7% as a conservative real-return estimate. Our compound interest investment calculator lets you test multiple rates instantly — simply drag the slider to see how different assumptions change your outcome.
Inflation erodes the purchasing power of your future balance. To account for it, use a real return rate instead of the nominal rate: subtract the expected inflation rate from your investment return. If your investment earns 9% and inflation averages 3%, your real return is approximately 6%. For a true wealth-building picture, enter the real rate in the annual rate field. The final balance the calculator shows will then represent today's purchasing power, not nominal future dollars. Use our Inflation Calculator to convert nominal values to real values.
Our free compound interest calculator is mathematically precise for the inputs provided. It applies the standard compound interest formula to the principal and the future-value-of-annuity formula to each month's contribution, compounding each at the selected frequency. Results assume a fixed, constant rate throughout the investment period. In reality, investment returns fluctuate year to year. Use the calculator as a planning tool to understand the potential of compounding, and consult a qualified financial advisor before making investment decisions. All calculations run entirely in your browser — no data is stored or shared.