Compound Interest Calculator
See how your investments grow over time with compound interest.
Investment Summary
Final Balance
$302,370.09
Total Contributions
$130,000.00
Interest Earned
$172,370.09
132.6% return
Effective Rate
7.23%
How Does Compound Interest Work?
Compound interest is one of the most powerful concepts in finance. Unlike simple interest, which is calculated only on the principal amount, compound interest is calculated on the principal plus all previously accumulated interest. This creates a snowball effect where your money grows faster and faster over time.
The compound interest formula is:
A = P(1 + r/n)nt
Where:
- A = Final amount (principal + interest)
- P = Principal (initial investment)
- r = Annual interest rate (as a decimal)
- n = Number of times interest compounds per year
- t = Number of years
For example, if you invest $10,000 at 7% annual interest compounded monthly for 20 years, your investment would grow to approximately $40,387.39 without any additional contributions. Adding regular monthly contributions accelerates this growth even further, which is why consistent investing is so important.
The key takeaway is that time is your greatest ally. The earlier you start investing, the more time compound interest has to work in your favor. Even small monthly contributions can grow into substantial wealth over decades.
Interest Compounded Monthly vs. Annually
At your current rate and compounding frequency, each dollar grows at an effective annual rate of 7.23%. Compounding monthly beats annually because interest is added 12 times a year instead of once, so you begin earning interest on your interest sooner.
$10,000 Growth Over Time
How a one-time $10,000 deposit grows at 7% compounded annually with no extra contributions. Over 10 years it reaches about $19,671.51.
| Years | Future Value | Interest Earned |
|---|---|---|
| 5 years | $14,025.52 | $4,025.52 |
| 10 years | $19,671.51 | $9,671.51 |
| 20 years | $38,696.84 | $28,696.84 |
| 30 years | $76,122.55 | $66,122.55 |
Frequently Asked Questions
What is compound interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is calculated only on the principal, compound interest allows your money to grow exponentially over time as you earn "interest on interest."
How does compound frequency affect my returns?
The more frequently interest compounds, the more you earn. Daily compounding yields slightly more than monthly, which yields more than quarterly or annually. However, the difference between monthly and daily compounding is relatively small. The biggest jump is from annual to quarterly or monthly compounding.
What is the Rule of 72?
The Rule of 72 is a simple way to estimate how long it takes for an investment to double. Divide 72 by your annual interest rate to get the approximate number of years. For example, at 8% interest, your money doubles in approximately 72 / 8 = 9 years.
How much should I invest monthly to reach my goal?
The amount depends on your target balance, time horizon, and expected return. Use this calculator to experiment with different monthly contribution amounts. Generally, starting early with consistent contributions, even small ones, is more effective than investing larger amounts later due to the power of compounding.
Is interest compounded monthly better?
Yes — for the same annual rate, monthly compounding earns slightly more than annual compounding because interest is added to your balance 12 times a year instead of once, so you begin earning interest on that interest sooner. At 7%, monthly compounding gives an effective annual rate of about 7.23% versus 7.00% for annual compounding, and the gap widens over long time horizons.
How much is compound interest on $10,000 over 10 years?
A one-time $10,000 deposit at 7% compounded annually grows to about $19,672 after 10 years — roughly $9,672 of that is compound interest. At 5% it would reach about $16,289, and at 10% about $25,937. Adding regular monthly contributions increases the total substantially.