Compound Interest Calculator
See how your money grows over time with compound interest, regular contributions, and inflation adjustment. Includes the Rule of 72, EAR, and what-if comparisons.
Investment Details
Contributions & Inflation optional
Added at the start of each month
Leave at 0 to skip inflation adjustment
Rule of 72
At 7% annual return, your money doubles every 10.3 years.
Formula: 72 ÷ interest rate = years to double
Final Balance
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After -- of compounding
Total Contributions
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Total Interest Earned
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Real Value (Inflation-Adj.)
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Effective Annual Rate
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Balance Over Time
Contributions vs. interest grown — stacked area
Year-by-Year Breakdown
| Year | Balance | Interest (Yr) | Total Contrib. | Total Interest |
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Download Investment Report (PDF)
Get a detailed PDF with your growth projection, year-by-year breakdown, and scenario comparisons.
What-If Comparison
See how small changes compound dramatically over time.
Your Scenario
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Base
5 Yrs Earlier
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+1% Rate
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All scenarios use same compounding frequency and monthly contributions.
Understanding Compound Interest
Worked Example: $10,000 Investment
Invest $10,000 at 7% annual return, compounded monthly, with $200/month contributions for 20 years.
- Total contributions: $58,000 ($10k initial + $48k in monthly additions)
- Total interest earned: $62,200+
- Final balance: $120,200+
Your money more than doubles thanks to compound growth. The $48,000 you contributed monthly earned more in interest than the contributions themselves.
Frequently Asked Questions
What is compound interest vs simple interest?
Simple interest only earns on the original principal. Compound interest earns interest on both the principal and previously earned interest. Over long periods, the difference is dramatic -- a $10,000 investment at 7% for 30 years grows to $76,123 with compound interest vs $31,000 with simple interest.
Does compounding frequency matter?
Yes, but less than you might think. Daily compounding at 7% yields an EAR of 7.25%, while annual compounding stays at 7%. The difference is meaningful over decades but small compared to the impact of your contribution rate and time in the market.
Why should I care about inflation-adjusted returns?
A dollar today buys more than a dollar in 20 years. At 3% inflation, your purchasing power roughly halves every 24 years. The "real return" (nominal return minus inflation) tells you how much your wealth actually grows in terms of buying power. A 7% nominal return with 3% inflation is effectively a 4% real return.