What is Compound Interest?
Compound interest is the interest on a deposit calculated based on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which only earns interest on the principal, compound interest earns interest on interest — creating exponential growth over time.
The compound interest formula is: A = P(1 + r/n)nt, where P is the principal, r is the annual rate, n is compounding frequency, and t is time in years.
Three Key Principles
- Start Early — Time is your greatest asset. The earlier you start investing, the more time compound interest has to grow your wealth.
- Stay Consistent — Regular contributions multiply your returns. Even small monthly investments compound significantly over decades.
- Be Patient — Growth accelerates over time. Compound interest shows its true power in the later years of an investment.
Investment Basics
Understanding fundamental investment concepts is essential for building long-term wealth.
- Principal
- The initial amount of money you invest. This is your starting point and the foundation of your investment.
- Interest Rate
- The percentage at which your money grows. Higher rates mean faster growth, but often come with higher risk.
- Compounding Frequency
- How often interest is calculated and added to your balance. More frequent compounding leads to higher returns.
- Regular Contributions
- Periodic additions to your investment. Consistent contributions dramatically accelerate wealth building.
- Time Horizon
- The length of time you plan to hold your investment. Longer horizons allow for more compound growth.
- Risk vs. Return
- Higher potential returns typically come with higher risk. Diversification helps manage this balance.
Rule of 72
A quick mental math shortcut to estimate how long it takes for your money to double: 72 ÷ Rate = Years to Double.
| Interest Rate | Years to Double |
|---|---|
| 3% | 24 years |
| 6% | 12 years |
| 8% | 9 years |
| 10% | 7.2 years |
| 12% | 6 years |
Financial Glossary
- APY (Annual Percentage Yield)
- The real rate of return on an investment, taking into account the effect of compounding interest.
- APR (Annual Percentage Rate)
- The annual rate charged for borrowing or earned through an investment, without accounting for compounding.
- Compound Interest
- Interest calculated on both the initial principal and the accumulated interest from previous periods.
- Diversification
- Spreading investments across various assets to reduce risk.
- ROI (Return on Investment)
- A measure of the profitability of an investment, calculated as (gain - cost) / cost × 100.
Frequently Asked Questions
What is compound interest?
Compound interest is interest calculated on the initial principal and also on the accumulated interest of previous periods. It makes your money grow faster than simple interest.
How does the Rule of 72 work?
Divide 72 by your annual interest rate to estimate how many years it will take for your investment to double. For example, at 8% interest, it takes approximately 9 years.
What is the difference between APR and APY?
APR (Annual Percentage Rate) does not account for compounding, while APY (Annual Percentage Yield) does. APY is typically higher because it includes the effect of interest on interest.
How often should I contribute to my investment?
The more frequently you contribute, the more you benefit from compound interest. Monthly contributions are a popular choice as they align with most income schedules.
Is this calculator free to use?
Yes, this compound interest calculator is completely free. All calculations run locally in your browser with no data collection.
How to Use This Calculator
- Set Your Currency — Choose from USD, EUR, GBP, JPY, KRW, or CNY.
- Enter Initial Investment — Input the amount you're starting with.
- Add Regular Contributions — Set how much you'll add regularly (daily, monthly, or yearly).
- Set Interest Rate — Enter your expected rate of return.
- Choose Duration — Select how long you plan to invest.
- Explore Results — View your projected growth in charts, tables, and summary cards.
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