Compound Interest Calculator
Calculate how your money grows with compound interest over time
What is Compound Interest?
Compound interest is the interest calculated on the initial principal, which also includes all of the accumulated interest from previous periods. Albert Einstein reportedly called it "the eighth wonder of the world."
Unlike simple interest where you only earn interest on your principal, compound interest allows your money to grow at an accelerating rate over time.
The Compound Interest Formula
A = P(1 + r/n)^(nt)
P = Principal
Your initial investment
r = Annual Rate
Expected return (decimal)
n = Frequency
Times compounded per year
t = Time
Years invested
How to Use This Calculator - Step by Step
Initial Investment
Enter the amount of money you have available to invest now.
Monthly Contribution
Amount you plan to add to your investment each month through regular investing.
Annual Return Rate
Your estimated annual return. Stock market historically averages 7-10%.
Investment Period
How long you plan to let your money grow. Minimum 5-10 years recommended.
Click "Calculate"
View detailed results including growth chart and investment breakdown.
Real-Life Example
Scenario: Start at age 25, invest $500/month, 8% annual return
After 10 years
~$91,000
Contributions: $60,000
After 20 years
~$298,000
Contributions: $120,000
After 30 years
~$750,000
Contributions: $180,000
Key Insight: By year 30, your interest earnings ($570,000+) far exceed your total contributions ($180,000)!
Expert Financial Tips
Start Early
The earlier you start, the more time compound interest has to work. A 10-year delay can double the required contribution.
Consistent Investing
Regular monthly contributions, regardless of market conditions, help smooth out volatility and build wealth over time.
Stay Invested
Time in the market beats timing the market. Don't interrupt the compounding process by frequent buying and selling.
Diversify
Spread investments across different asset classes to reduce risk while maintaining growth potential.
Frequently Asked Questions
Q: Does compounding frequency matter?βΌ
A: Yes, but the difference is small for long-term investing:
- Annual compounding (n=1): ~$21,589 after 10 years
- Monthly compounding (n=12): ~$22,080 after 10 years
- Daily compounding (n=365): ~$22,133 after 10 years
The difference is about 2.5% - choose the frequency that works best for your situation.
Q: What is a realistic expected return?βΌ
A: Different investments have different risk-return profiles:
- Savings accounts: 2%-4% (low risk)
- Bond funds: 4%-6% (low-medium risk)
- Stock index funds: 7-10% long-term average (higher risk)
- Individual stocks: Variable, higher volatility
Higher returns typically come with higher risk. Choose based on your risk tolerance.
Q: How much money do I need to start?βΌ
A: There is no minimum to start benefiting from compound interest:
- Even $100/month can grow significantly over time
- Starting early matters more than starting big
- Many brokerages offer zero-minimum accounts
The magic of compound interest is about time, not the size of your initial investment.
Q: Does inflation affect compound interest returns?βΌ
A: Yes. You need to subtract inflation from your nominal return to get the real return.
Example:
- Nominal return: 8%
- Inflation rate: 3%
- Real return: approximately 5%
Consider "real purchasing power growth" rather than just the nominal numbers.
Q: What's the difference between simple and compound interest?βΌ
A: The key difference is how interest is calculated:
- Simple Interest: Interest calculated only on principal. You earn the same amount each year.
- Compound Interest: Interest calculated on principal + accumulated interest. Growth accelerates over time.
Over long periods, compound interest can significantly outperform simple interest.