Investment Calculator
Calculate how much your investments will grow over time, compute return on investment (ROI), and find the compound annual growth rate (CAGR) of any investment. Discover the dramatic impact of regular monthly contributions and the cost of starting late.
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How It Works
FV = P(1+r/n)^(nt) + PMT x [(1+r/n)^(nt) - 1] / (r/n). The first term covers lump sum growth. The second covers regular contribution growth. Together they model the compounding power of consistent long-term investing.
FV = P(1+r)^t + PMT x [(1+r)^t - 1] / r$10K + $500/mo at 7% for 30yr = $612,285ROI shows the total percentage gain: (Return minus Investment) / Investment x 100%. Annualizing it gives CAGR, which lets you compare investments held for different lengths of time on an equal basis.
ROI% = (Gain / Invested) x 100$10K invested returns $18K total = 80% ROI overallCAGR = (End / Start)^(1/years) minus 1. This single annualized rate would produce the same result as the actual investment path. Use CAGR to compare any two investments regardless of how long they were held.
CAGR = (End/Start)^(1/n) - 1$10K grows to $18K in 5 years = 12.5% CAGR per yearEven small regular contributions compound dramatically over time. $200 per month at 7% for 30 years accumulates $234,000 from contributions alone, on top of any lump sum invested. Starting early and staying consistent matters most.
Contribution FV = PMT x [(1+r)^n - 1] / r$200/month at 7% for 30 years = $234,000 from contributionsDivide 72 by the annual return rate to estimate years to double your money. At 7% annual return: 72 / 7 = approximately 10.3 years to double. The exact formula uses natural logarithm but the Rule of 72 is accurate within a few months.
Doubling time approximately 72 / annual return %$50K at 9% annual return doubles in approximately 8 yearsSubtract the inflation rate from your nominal return to find the real return in purchasing power. At 7% nominal return and 3% inflation, your real return is approximately 4%. For long-term planning always think in real terms.
Real return approximately = nominal - inflation rate7% nominal minus 3% inflation = about 4% real annual returnQuick Reference
Common examples — verify instantly above.
7% for 30 years
$10,000 lump sum only
$76,123 final value
With contributions
$10K + $500/mo, 7%, 30yr
$612,285 final value
ROI example
$10K invested, $18K returned
80% ROI total
CAGR example
$10K to $18K in 5 years
12.5% CAGR per year
Rule of 72 at 7%
Doubling time estimate
Approximately 10.3 years
Rule of 72 at 10%
Doubling time estimate
Approximately 7.2 years
Fee impact
$100K at 7% with 1% fee
$130K+ in lost returns
Start at 25 vs 35
$5,000 at 7% to age 65
$75K vs $38K — huge gap
Tips & Shortcuts
Start investing as early as possible. The gap between starting at 25 versus 35 can mean hundreds of thousands of dollars by retirement due to compounding.
Low-cost index funds with expense ratios below 0.1% consistently outperform most actively managed funds over 15-year periods or longer.
Max out tax-advantaged accounts first — 401k up to the employer match, then IRA — before investing in taxable brokerage accounts.
Dollar-cost averaging by investing a fixed amount each month removes emotional timing decisions and reduces the risk of investing at a peak.
Rebalance your portfolio annually by selling outperformed assets and buying underperformed ones to maintain your target allocation.
Use CAGR when evaluating any investment claim. A good long-term investment should consistently beat inflation and approach historical market returns.
Common Mistakes to Avoid
Trying to time the market
Research consistently shows staying fully invested outperforms trying to buy low and sell high. Missing just the 10 best market days in a decade dramatically reduces overall returns.
Ignoring expense ratios and investment fees
A 1% annual fee seems small but costs over $130,000 on a $100K investment at 7% over 30 years due to compound effects. Choose low-cost index funds.
Planning in nominal returns without accounting for inflation
A 7% nominal return with 3% inflation gives only 4% real purchasing power growth. Always use inflation-adjusted real returns for long-term financial projections.
Leaving significant cash uninvested for extended periods
Cash earning 1% to 5% loses real purchasing power when inflation runs at 3%. Money not deployed in growth assets loses real value over time.
Stopping contributions during market downturns
Market drops mean asset prices are lower. Stopping contributions during downturns means buying fewer shares at the best prices and missing the subsequent recovery.
Concentrating in single stocks or sectors
Even excellent companies can fail or stagnate for years. Broad diversification across sectors, countries, and asset classes reduces risk without proportionally reducing expected returns.
Frequently Asked Questions
The S&P 500 has historically returned approximately 10% per year on average, or about 7% after inflation. A diversified portfolio of stocks and bonds might return 6% to 8% long-term. Past performance does not guarantee future results and any specific year can vary dramatically.
ROI (Return on Investment) shows the total percentage return regardless of how long the investment was held: (Gain / Investment) x 100%. CAGR (Compound Annual Growth Rate) shows the equivalent annualized return: (End / Start)^(1/years) minus 1. Use CAGR to compare investments held for different periods.
A common guideline is to invest 15% of gross income for retirement. If saving for a specific goal, use the Future Value calculator to work backwards — enter your target amount, expected rate, and years to find the required monthly contribution.
Start as early as possible. Due to compound growth, $5,000 invested at age 25 grows to approximately $75,000 by age 65 at 7% annually. The same amount invested at age 35 grows to only $38,000. Starting 10 years earlier nearly doubles the final result.
Fees compound against your wealth just as returns compound for it. A 1% annual fee on a $100,000 investment growing at 7% for 30 years costs over $130,000 in lost returns. Always seek low-cost index funds with expense ratios below 0.1%.
Dollar-cost averaging means investing a fixed amount at regular intervals regardless of market conditions. When prices are high you buy fewer shares. When prices are low you buy more shares. Over time this reduces the risk of investing a large sum at a market peak.
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