Compound Interest Visualizer
See how your money grows over time with . Adjust principal, monthly contributions, interest rate, and time horizon.
Future Value
$486.2K
$486,172
Total Invested
$130.0K
$130,000
Interest Earned
$356.2K
73% of total
Growth Multiple
3.7×
over 20 years
What this means
Most growth arrives in the final years
At 10.5% annual return, money doubles roughly every 7 years. Starting early with $10,000 is usually the biggest lever.
The assumed rate changes everything over decades
A one-point difference in return can materially change the result over long periods.
Taxes erode compounding
Taxes and fees reduce the effective return in taxable accounts.
Suggested next step
Project what consistent investing could look like over 20–30 years.
Stress-test with compound interest →Portfolio Growth Over 20 years
Year-by-Year Milestones
| Year | Total Value | Contributions | Interest earned |
|---|---|---|---|
| Start | $10,000 | $10,000 | $0 |
| Year 5 | $56,100 | $40,000 | $16,100 |
| Year 10 | $133,854 | $70,000 | $63,854 |
| Year 15 | $264,993 | $100,000 | $164,993 |
| Year 20 | $486,172 | $130,000 | $356,172 |
Want to see what this rate looked like historically?
Run real historical data in the Investment Calculator - pick any stock or ETF and see actual past returns.
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Frequently Asked Questions
- What is compound interest?
- Compound interest means you earn interest on your interest, not just on your original deposit. Over time, this creates exponential growth - your money earns more and more each year as the base keeps growing. Albert Einstein reportedly called it the "eighth wonder of the world."
- How does compound interest differ from simple interest?
- Simple interest only applies to your original principal. Compound interest applies to your growing balance - principal plus all previously earned interest. For long-term investing, the difference is dramatic: a $10,000 investment at 10% for 30 years earns $30,000 in simple interest but over $164,000 compound.
- Why is the S&P 500 preset at 10.5%?
- The S&P 500 has delivered approximately 10–11% average annual return before inflation since 1957. This is a long-run historical average - individual years vary widely, from −37% (2008) to +32% (2013). Past performance does not guarantee future results.
- How does monthly contribution frequency affect growth?
- Contributing monthly instead of annually means each dollar starts compounding sooner. This "dollar-cost averaging" approach also reduces the impact of market volatility on large lump-sum investments. Even small monthly contributions add up dramatically over decades.
- What is the Rule of 72?
- The Rule of 72 is a quick mental shortcut: divide 72 by your annual interest rate to estimate how long it takes to double your money. At 7.2%, money doubles in ~10 years. At 10%, it doubles in ~7.2 years. This tool lets you see the full picture beyond just the doubling point.
- Does this account for inflation?
- No - the calculator shows nominal returns (before inflation). To estimate real (inflation-adjusted) returns, subtract the inflation rate from your interest rate. For example, at 10% return with 3% inflation, your real rate is approximately 7%. A conservative after-inflation long-term rate for equities is around 6–7%.
- What about taxes and fees?
- This visualizer does not include taxes or fund fees (expense ratios). In a tax-advantaged account (401k, IRA, Roth IRA), your full return compounds without annual tax drag. In taxable accounts, dividends and capital gains taxes reduce effective returns. Index funds typically have very low fees (0.03–0.20%), but actively managed funds can charge 1%+ annually.
How to use this tool
Build a simple compounding plan in under a minute.
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Step 1
Enter your starting balance
Set the amount you already have invested or saved.
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Step 2
Add monthly contribution and expected return
Use realistic values first, then test optimistic and conservative cases.
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Step 3
Set time horizon
Choose the number of years to see how long-term compounding changes outcomes.
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Step 4
Read chart and milestones
Compare contributions vs growth and inspect the year-by-year checkpoints.
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, it grows your full balance over time, including previously earned returns.
How often does compound interest compound in this calculator? ▼
This calculator compounds annually by default, which is standard for long-term investment projections. Monthly compounding produces slightly higher results and is available in the advanced settings.
What is a realistic expected return rate to enter? ▼
The S&P 500 has averaged approximately 10–10.5% per year before inflation over the long term. A conservative estimate for a diversified portfolio is 6–7%. For a savings account or bonds, 3–5% is more appropriate.
How do monthly contributions affect compound growth? ▼
Monthly contributions significantly accelerate compound growth, especially over long time horizons. Each new contribution starts compounding immediately, so even small regular additions can dwarf the growth from a one-time investment over 20–30 years.
Does this calculator account for inflation or taxes? ▼
No — results are shown in nominal (pre-inflation, pre-tax) terms for simplicity. To approximate real purchasing power, subtract your expected annual inflation rate from the return rate you enter.
Compound Interest Calculator & Visualizer
How your money compounds over time
Compound interest is the engine of long-term wealth. Unlike simple interest, it grows your full balance over time - including previously earned returns. Use this visualizer to test scenarios from conservative savings assumptions to long-run equity-style growth rates.
Key Features
- Interactive sliders update the chart instantly - no page reload required.
- Stacked area chart clearly separates contributions from interest earned.
- Year-by-year milestone table shows your exact balance at 5-year intervals.
- Two presets: S&P 500 historical average (~10.5%) and a conservative 6% rate.
- Fully accessible: keyboard-navigable, screen-reader friendly, mobile-first.
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Next step
Turn compound assumptions into a monthly action planBridge theory and execution with timeline-based targets.