Compound Interest Planner
Harness the power of exponential growth. Plan your path to financial freedom by visualizing how small, consistent contributions build massive wealth over time.
The Architect of Wealth
Albert Einstein famously called compound interest the "eighth wonder of the world." He said, "He who understands it, earns it... he who doesn't... pays it." Our Compound Interest Planner is designed to help you understand (and earn) it. Whether you are saving for retirement, a child's education, or just a rainy day, seeing the long-term impact of your savings habits is the best motivation to start today.
The Snowball Effect
Compounding is like rolling a snowball down a hill. At first, it's small and grows slowly. But as it rolls, the surface area gets bigger, picking up more snow with every rotation.
Linear Growth (Simple Interest)
You earn $100 every year. After 10 years, you have $1,000 profit. A straight line.
Exponential Growth (Compound)
You earn 10% on your balance. Each year the balance is bigger, so the 10% payout is bigger. The curve shoots upward.
Key Inputs Explained
To get the most accurate projection:
- Principal: The lump sum you have invested right now.
- Monthly Addition: The new money you save from your paycheck every month.
- Years to Grow: The duration of the investment. Time is the most powerful variable in compounding.
- Interest Rate: Your expected Rate of Return. Use 7-10% for stocks, 4-5% for bonds, 0-1% for savings accounts.
Retirement (FIRE)
Want to retire early? Use this tool to calculate your "Coast FIRE" number—the point where you can stop contributing and let compounding finish the job.
College Fund
Start a 529 plan when your child is born. Even $200/month can grow into a substantial tuition fund over 18 years.
Millionaire Math
Find out exactly how much you need to save per month to have $1,000,000 by age 65. The answer might surprise you (it's less than you think).
Frequently Asked Questions
Does compounding work for debt too?
Unfortunately, yes. Credit card debt compounds against you. This is why high-interest debt spirals out of control so quickly. You pay interest on your interest.
How often is interest compounded?
In the stock market, growth isn't guaranteed daily, but generally follows an annual trend. Savings accounts usually compound daily or monthly. Our calculator assumes monthly compounding for realistic results.
What is the Rule of 72?
The Rule of 72 is a mental math shortcut. Divide 72 by your interest rate to see how many years it takes to double your money. At 8% returns, your money doubles every 9 years (72/8 = 9).
Projection Disclaimer
Market returns are never guaranteed. Past performance data (like the S&P 500 average) does not predict future results. Inflation may reduce the purchasing power of future simulations.
Data Privacy
We do not store your financial data. This calculator runs entirely in your browser.