Compound interest calculator
See how your money grows over time. Adjust your initial investment, monthly contributions and interest rate to plan ahead.
Investment parameters
Key insights
Understanding the principles behind compound interest.
- The Rule of 72
Divide 72 by your annual interest rate to estimate how many years it takes to double your money.
At 7% annual return, your money doubles in approximately 10.3 years
- Power of starting early
Time is your greatest ally. Starting just 5 years earlier can make a dramatic difference in your final balance.
Starting 5 years earlier would grow to approximately $433,769
- Compounding frequency
More frequent compounding means your interest earns interest sooner, resulting in slightly higher returns over time.
- monthlySelected
- $300,851
- quarterly
- $297,755
- annually
- $284,670
Frequently asked questions
Common questions about compound interest and this calculator.
- What is compound interest and how does it work?
- Compound interest is the interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which only earns on the original amount, compound interest allows your money to grow exponentially over time. For example, if you invest $1,000 at 7% annual interest, after one year you have $1,070. In the second year, you earn 7% on $1,070 (not just $1,000), giving you $1,144.90. This snowball effect is what makes compound interest so powerful for long-term wealth building.
- How does compounding frequency affect my returns?
- The more frequently interest is compounded, the more you earn. Monthly compounding produces slightly higher returns than quarterly, which beats annual compounding. For example, $10,000 at 7% for 20 years yields approximately $38,697 with annual compounding, $39,365 with quarterly, and $40,387 with monthly compounding. While the difference may seem small per year, it adds up significantly over decades.
- What is the Rule of 72?
- The Rule of 72 is a quick way to estimate how long it takes for an investment to double. Simply divide 72 by your annual interest rate. For example, at 7% annual return, your money doubles in approximately 72 / 7 = 10.3 years. At 10%, it doubles in about 7.2 years. This rule is a useful mental shortcut for evaluating investment opportunities and understanding the power of different return rates.
- How important are regular monthly contributions?
- Regular monthly contributions can dramatically increase your final wealth thanks to dollar-cost averaging and compounding. For instance, investing $10,000 once at 7% for 20 years grows to about $40,000. But adding just $500 per month transforms that into over $270,000. The consistent additions give compound interest more principal to work with each month, creating a powerful wealth-building engine.
- What annual return rate should I use in my calculations?
- The appropriate rate depends on your investment strategy. Historically, the S&P 500 has averaged about 10% annually before inflation, or roughly 7% after inflation. A diversified portfolio of stocks and bonds might target 6-8%. Conservative investments like high-yield savings or bonds typically return 2-5%. For planning purposes, using 7% is a reasonable middle ground for a balanced portfolio. Always remember that past performance does not guarantee future results.
Disclaimer
This calculator is provided for informational and educational purposes only. The results are estimates based on the inputs you provide and assume a constant rate of return. Actual investment performance will vary due to market fluctuations, fees, taxes, and other factors. This tool does not constitute financial advice. Please consult a qualified financial advisor before making investment decisions.
By the numbers
What the data says
- Year-end 2024
$38,176
Median 401(k) balance among Vanguard plan participants
The average is $148,153, skewed by large accounts
Source: Vanguard, How America Saves 2025 - July 2025
14%
US adults who own cryptocurrency
Source: Gallup - 2022 survey
$192,900
Median net worth of US families
The mean is about $1.06 million, pulled up by the wealthiest households
Source: Federal Reserve, Survey of Consumer Finances
National figures from the sources shown, as of the period on each card. They are context, not a forecast or advice for your situation.
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