Compound Interest Calculator
Free compound interest calculator to see how your investments grow. Calculate daily, monthly, and annual compounding. See year-by-year growth projections and plan your FIRE journey.
Total Balance
$302,370
Total Contributions
$130,000
Total Interest Earned
$172,370
Year-by-Year Breakdown
| Year | Starting Balance | Contribution | Interest | Ending Balance |
|---|---|---|---|---|
| 1 | $10,000 | $6,000 | $955 | $16,955 |
| 2 | $16,955 | $6,000 | $1,458 | $24,413 |
| 3 | $24,413 | $6,000 | $1,997 | $32,411 |
| 4 | $32,411 | $6,000 | $2,575 | $40,986 |
| 5 | $40,986 | $6,000 | $3,195 | $50,182 |
| 6 | $50,182 | $6,000 | $3,860 | $60,042 |
| 7 | $60,042 | $6,000 | $4,573 | $70,614 |
| 8 | $70,614 | $6,000 | $5,337 | $81,952 |
| 9 | $81,952 | $6,000 | $6,157 | $94,108 |
| 10 | $94,108 | $6,000 | $7,036 | $107,144 |
| 11 | $107,144 | $6,000 | $7,978 | $121,122 |
| 12 | $121,122 | $6,000 | $8,988 | $136,110 |
| 13 | $136,110 | $6,000 | $10,072 | $152,182 |
| 14 | $152,182 | $6,000 | $11,234 | $169,416 |
| 15 | $169,416 | $6,000 | $12,480 | $187,895 |
| 16 | $187,895 | $6,000 | $13,815 | $207,710 |
| 17 | $207,710 | $6,000 | $15,248 | $228,958 |
| 18 | $228,958 | $6,000 | $16,784 | $251,742 |
| 19 | $251,742 | $6,000 | $18,431 | $276,173 |
| 20 | $276,173 | $6,000 | $20,197 | $302,370 |
What Is Compound Interest and Why Does It Matter for FIRE?
Albert Einstein reportedly called compound interest the "eighth wonder of the world." For FIRE (Financial Independence, Retire Early) seekers, it's the engine that makes early retirement possible. Unlike simple interest, which only earns returns on your principal, compound interest earns returns on both your principal and your accumulated interest — creating a snowball effect that accelerates your wealth building over time. The earlier you start investing, the more powerful compounding becomes. Use our free compound interest calculator above to see exactly how your money can grow with different starting amounts, monthly contributions, and return rates.
How to Use This Compound Interest Calculator
- Initial Investment — Enter your current savings or starting amount.
- Monthly Contribution — Set how much you plan to invest each month. Even $500/month can grow to over $1 million with enough time.
- Annual Return — Choose your expected annual return rate. The S&P 500 has historically returned ~10% before inflation (7% after inflation).
- Years — Set your investment time horizon. The longer, the better — time is the most powerful variable in compound interest.
- Compound Frequency — Choose daily, monthly, or annual compounding. More frequent compounding yields slightly higher returns.
The year-by-year breakdown table shows exactly how much comes from your contributions vs. investment returns, helping you understand the power of passive growth.
Frequently Asked Questions About Compound Interest
What is compound interest?
Compound interest is interest earned on both your original principal and on previously accumulated interest. For example, if you invest $10,000 at 7% annual return, after year 1 you have $10,700. In year 2, you earn 7% on $10,700 (not just $10,000), giving you $11,449. Over decades, this compounding effect creates exponential growth — which is why starting early is so important for FIRE.
How does compound frequency affect my returns?
Compound frequency determines how often interest is calculated and added to your balance. Daily compounding yields the highest returns, followed by monthly, then annual. For example, $10,000 at 7% for 10 years grows to about $19,672 with annual compounding, $20,097 with monthly compounding, and $20,136 with daily compounding. While the differences seem small year-to-year, they add up significantly over 20-30 year periods.
What is a realistic annual return rate to use in the calculator?
The S&P 500 has historically returned about 10% per year before inflation, or roughly 7% after inflation. For FIRE planning, many people use 7% as a conservative real return estimate. If you want to be more conservative, use 5-6%; if you're optimistic, use 8-9%. We recommend running multiple scenarios to see how different return rates affect your outcome.
How much should I invest monthly to reach FIRE early?
The FIRE movement encourages saving 50-70% of your income. The exact amount depends on your FIRE number and timeline. Use our compound interest calculator to model different monthly contributions — even small increases make a huge difference over decades. For example, investing an extra $200/month for 20 years at 7% adds over $100,000 to your final balance.
What is the difference between simple interest and compound interest?
Simple interest only earns returns on your original principal. For example, $10,000 at 7% simple interest for 10 years = $17,000 ($7,000 in interest). With compound interest (compounded annually), the same investment grows to $19,672 — an extra $2,672 from compounding. Over 30 years, the difference is even more dramatic: $31,000 with simple interest vs. $76,123 with compound interest.