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Free Investment Calculator

Watch Your Money
Compound Over Time

See exactly how your savings grow with the power of compound interest. Adjust your inputs and watch the chart update in real time.

Future Value
$0
Total balance at end of period
—
Total Interest Earned
$0
Growth on top of contributions
Total Contributions
$0
Principal + all deposits made
Calculator Inputs
Initial Investment $5,000
$0$100k
$
Monthly Contribution $200
$0$5k/mo
$
Annual Interest Rate 7.00%
0.1%25%
%
Time Period 20 yrs
1 yr50 yrs
yrs
Adjust for Inflation
Show real purchasing power (3% avg inflation)
Growth Over Time
Total Value
Contributions
Interest
Year-by-Year Breakdown
Year Opening Balance Contributions Interest Earned Closing Balance Total Growth

What is Compound Interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, it causes wealth to grow exponentially — the longer you wait, the faster it accelerates.

The Rule of 72

Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 7% returns, your money doubles roughly every 10.3 years. At 10%, every 7.2 years. It's a powerful mental shortcut.

Why Monthly Contributions Matter

Even small regular contributions dramatically accelerate growth. Adding $200/month to a $5,000 investment at 7% over 20 years adds over $100,000 compared to investing the lump sum alone. Time and consistency beat timing the market.

Compounding Frequency

The more frequently interest compounds, the more you earn. Daily compounding earns slightly more than monthly, which earns more than annually — though the difference shrinks at typical savings rates. Most investment accounts compound monthly or daily.

Frequently Asked Questions
What interest rate should I use? ▾
It depends on where your money is invested. High-yield savings accounts currently offer 4–5% APY. The US stock market (S&P 500) has historically averaged about 10% annually, or roughly 7% after adjusting for inflation. Bonds average 3–5%. For long-term retirement planning, most financial advisors suggest using 6–8% as a conservative stock market estimate.
What is the compound interest formula? ▾
The formula is: A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)] — where A is the final amount, P is the principal, r is the annual interest rate (as a decimal), n is the number of compounding periods per year, t is time in years, and PMT is the periodic contribution amount.
How does inflation affect my investment? ▾
Inflation erodes purchasing power over time. $100,000 in 20 years won't buy what $100,000 buys today. Toggle "Adjust for Inflation" to see results in today's dollars using a 3% average inflation rate. This gives you a more realistic picture of your actual future wealth. The "real" return on an investment is roughly the nominal rate minus inflation.
What's the difference between APY and APR? ▾
APR (Annual Percentage Rate) is the simple annual interest rate without compounding. APY (Annual Percentage Yield) accounts for compounding and shows what you actually earn in a year. A savings account with 5% APR compounding monthly has an APY of about 5.12%. Always compare APY when evaluating savings accounts.
Is this calculator accurate for stocks or ETFs? ▾
This calculator assumes a fixed, consistent rate of return — which is a simplification. Stock markets fluctuate year to year, and real returns vary significantly. Use it for general projections and planning, not as a guarantee. For tax-advantaged accounts (401k, IRA, 401(k)/IRA), actual returns may differ due to tax treatment of gains and contributions.
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How to Use the Compound Interest Calculator

See exactly how your money grows over time with the power of compounding.

01
Enter your starting amount
This is the money you have today — your initial deposit or current investment balance.
02
Set your annual interest rate
Use your account's APY (Annual Percentage Yield) or your expected investment return. Stock market historical average is ~7% inflation-adjusted.
03
Choose your compounding frequency
Daily compounding earns slightly more than monthly, which earns more than annual. Most savings accounts compound daily. Most investment accounts are modelled annually.
04
Set your time period
Enter the number of years you plan to let the money grow. Notice how dramatically longer timeframes affect the result — this is the 'miracle of compounding'.
05
Add monthly contributions
Even small regular contributions have an enormous impact. Try adding $100/month and watch the final balance multiply.
06
Read the growth chart
The curved line is the key insight — money doesn't grow linearly, it accelerates. The longer you wait, the steeper the curve.
💡
💡 Try the Rule of 72: divide 72 by your interest rate to find how many years it takes to double your money. At 7%, money doubles every ~10.3 years.