Compound Interest Calculator
See how your money grows over time with the power of compound interest.
Final Balance
$300,851
Total Contributed
$130,000
Interest Earned
$170,851
Growth Over Time
Advertisement
The Complete Guide to Compound Interest
How to Use This Calculator
Enter your starting amount
This is the initial lump sum you're investing today. It could be money in a savings account, an inheritance, or the balance in a brokerage account. If you're starting from zero, set this to $0 — the calculator works just as well with monthly contributions alone.
Set your monthly contribution
This is the amount you plan to add every month going forward. Consistency matters more than the amount. Even $100 per month invested at a 7% average annual return grows to over $120,000 in 20 years. The key is picking a number you can stick with and automating it so you don't have to think about it.
Choose your expected return rate
The S&P 500 has historically returned about 10% per year before inflation, or roughly 7% after inflation, based on data going back to 1926 (source: NYU Stern). A 7% rate is a reasonable starting point for a diversified stock portfolio over a long time horizon. For a more conservative mix with bonds, try 5-6%. For a high-yield savings account, use 4-5%.
Set your time horizon
This is how long you plan to let the money grow. Compound interest accelerates over time — the last 10 years of a 30-year investment typically generate more growth than the first 20 years combined. If you're in your 20s or 30s, even a modest monthly contribution has decades to compound.
Understanding Your Results
Final balance
This is the projected total value of your investment at the end of your chosen time period. It includes both your contributions and all the interest earned along the way. Keep in mind this is a projection based on a constant rate of return — actual market returns will vary year to year, but the long-term average tends to smooth out.
Total contributed vs. interest earned
These two numbers show you the power of compounding. The gap between what you put in and what you end up with is the interest your money earned on its own. Over long periods, the interest earned often exceeds the total amount you personally contributed. That's the whole point — your money starts working harder than you do.
The growth chart
The green area shows your total balance over time, while the dashed gray line shows just your contributions. The widening gap between the two lines is compound interest in action. Notice how the curve gets steeper toward the end — that's exponential growth. The earlier you start, the more dramatic that curve becomes.
Investment Starter Guide
A beginner-friendly guide to compound interest, account types, asset allocation, and common investing mistakes to avoid.
Instant download. You'll also receive our free weekly financial tips newsletter. Unsubscribe anytime.
Frequently Asked Questions
Related Articles
Recession Investing: Build Wealth When Markets Are Down
Discover how to strategically invest during a recession, turning market downturns into opportunities for long-term wealth growth. Learn actionable steps and avoid common pitfalls.
Read article
Target Date Funds: Are They Right for Your Retirement?
Target date funds offer a 'set it and forget it' approach to retirement investing, but are they the best choice for your unique financial goals? Discover their pros and cons.
Read article
Roth IRA vs. Traditional IRA: Which One Should You Open?
Unsure whether a Roth or Traditional IRA is right for you? This guide breaks down the tax benefits, contribution rules, and flexibility of each to help you decide.
Read articleLike this calculator?
Get weekly money tips and strategies delivered to your inbox. Free, practical, and actionable.
Free forever. Unsubscribe anytime. No spam.