See how your money grows over time with the power of compound interest.
Our free compound interest calculator helps you understand how your investments can grow over time through the power of compounding. Whether you're saving for retirement, a major purchase, or simply building wealth, this calculator gives you a clear picture of your financial future.
Compound interest is often called "interest on interest" - it's when your investment earnings are added to your principal, forming a larger base for future interest calculations. Over time, this creates a powerful snowball effect that can dramatically increase your wealth.
As Albert Einstein allegedly said, "Compound interest is the eighth wonder of the world. He who understands it, earns it; he who doesn't, pays it."
To calculate your potential investment growth, follow these steps:
Our calculator uses these standard compound interest formulas:
For a one-time investment:
A = P(1 + r/n)^(nt)
For regular contributions (end of period):
A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)]
For regular contributions (beginning of period):
A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)] × (1 + r/n)
Where:
For continuous compounding, the formula is:
A = P × e^(rt)
Where e is the mathematical constant approximately equal to 2.71828.
The earlier you start investing, the more powerful compounding becomes. For example, if you invest $10,000 at age 25 with an 7% annual return, by age 65 it would grow to approximately $149,744. If you wait until age 35 to make the same investment, it would only grow to $76,122 by age 65.
This demonstrates why financial experts often say that time in the market is more important than timing the market.
A quick way to estimate how long it will take your money to double is to use the "Rule of 72." Simply divide 72 by your expected annual rate of return. For example, at 8% interest, your money would double in approximately 72 ÷ 8 = 9 years.
Even a seemingly small difference in interest rates can dramatically affect your final balance over long periods. For example, $10,000 invested for 30 years at 6% will grow to about $57,434. The same investment at 8% will grow to $100,626 – a difference of $43,192 from just a 2% higher return.
Savings accounts typically offer the lowest returns but with virtually no risk. They're FDIC-insured up to $250,000, making them safe places for emergency funds or short-term savings. Interest on these accounts usually compounds daily or monthly.
CDs usually offer higher interest rates than savings accounts in exchange for locking in your money for a set period (typically 3 months to 5 years). They're also FDIC-insured and generally compound daily. Early withdrawal penalties make them best for money you won't need for a known period.
Bonds can offer higher returns than bank products, with varying levels of risk depending on the issuer. Treasury bonds (very safe) typically yield less than corporate bonds (higher risk). Interest from bonds may be paid periodically rather than being automatically reinvested, but you can create a compounding effect by reinvesting the interest payments.
Individual stocks and ETFs (Exchange-Traded Funds) can provide higher potential returns over the long term, though with more short-term volatility. Compounding occurs through price appreciation and reinvested dividends. The S&P 500 has historically returned an average of about 10% annually before inflation (around 7% after inflation).
REITs allow you to invest in real estate without directly buying property. They typically pay higher dividends than many stocks and can be part of a compound growth strategy when those dividends are reinvested. They may offer both income and potential appreciation.
401(k)s, IRAs, and other retirement accounts aren't investments themselves but are tax-advantaged containers for your investments. The tax benefits allow more of your money to stay invested and compound over time, making them powerful wealth-building tools.
Simple interest is calculated only on the initial principal. If you invest $1,000 at 5% simple interest, you'll earn $50 each year regardless of the accumulated interest. With compound interest, you earn interest on both the principal and previously earned interest. The same $1,000 at 5% compounded annually would earn $50 in the first year, but in the second year, you'd earn 5% on $1,050, which is $52.50, and so on, with the interest amount growing each year.
More frequent compounding results in higher returns. For example, $10,000 invested at 8% for 10 years would grow to $21,589 with annual compounding, but to $22,196 with monthly compounding. The difference becomes more significant with higher interest rates and longer time periods. Continuous compounding represents the mathematical limit of compounding frequency and provides the highest possible return for a given interest rate.
The effective annual rate (EAR) is the actual annual interest rate when accounting for compounding frequency. If an investment offers 8% compounded monthly, the EAR is about 8.3%, meaning you effectively earn 8.3% annually due to the compounding effect. This allows for more accurate comparisons between investments with different compounding frequencies.
A common guideline is to have 25 times your annual expenses saved for retirement (the "4% rule"). To reach this goal, consistency is key. For example, investing $500 monthly for 30 years at a 7% average annual return would grow to about $567,000. Your specific needs may vary based on your desired lifestyle, expected retirement age, other income sources, health considerations, and inflation expectations. Use our calculator to test different scenarios and consult with a financial advisor for personalized guidance.
Taxes can significantly impact your compound growth. In taxable accounts, you may pay taxes annually on interest, dividends, or realized capital gains, reducing the amount that compounds. Tax-advantaged accounts like 401(k)s and IRAs allow your investments to grow tax-deferred or tax-free (in the case of Roth accounts), maximizing the compounding effect. Our calculator includes an optional tax rate input to help you see the potential impact of taxes on your investment growth.
A 7% inflation-adjusted annual return is considered a reasonable long-term expectation for a diversified stock portfolio based on historical performance of the S&P 500. However, actual returns will vary year to year, sometimes dramatically. More conservative investments like bonds and CDs will likely return less, while more aggressive investments might potentially return more but with higher risk. Your personal return will depend on your asset allocation, investment selection, market conditions, and time horizon.
Inflation reduces the purchasing power of money over time. If your investments grow at 7% annually but inflation is 3%, your real (inflation-adjusted) return is only about 4%. For long-term planning, it's important to consider returns in real terms. Bond yields and bank interest rates are often quoted in nominal terms (before inflation), while long-term stock market return estimates are sometimes quoted in real terms (after inflation). Our calculator uses nominal rates, so you may want to subtract your expected inflation rate from your projected returns to see the future value in today's dollars.
Contributing at the beginning of each period (whether monthly, quarterly, or annually) will result in slightly higher returns because your money has more time to compound. This approach is sometimes called "beginning of period" or "advance" contributions. For example, $1,000 invested monthly at 8% for 30 years would grow to about $1,447,000 with beginning-of-period contributions, versus about $1,397,000 with end-of-period contributions - a difference of about $50,000. Our calculator allows you to select either option to match your actual contribution pattern.