Doubling Time Calculator: Predict Investment Growth with Continuous Compounding
Enter your annual return, press calculate, and the tool shows the exact years, months and days until your money doubles with continuous compounding. Example: at the long-term 7 % average U.S. equity return, an investment doubles in about 10.3 years (Damodaran, 2023).
Doubling Time Calculator
Doubling Time:
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How to use the tool
Step 1 – Rate of Return (%): Type your expected annual return, e.g., 3.8 or 15.
Step 2 – Calculate: Click “Calculate” to run the formula instantly.
Step 3 – Read the result: The answer appears in years, months, and days.
Step 4 – Compare scenarios: Change the rate to see how faster returns shorten doubling time.
The formula the calculator uses
$$T = rac{\ln(2)}{r}$$
T – doubling time in years.
r – annual rate of return expressed as a decimal.
Example calculations
3.8 % return: r = 0.038 ⇒ T = 0.6931 / 0.038 ≈ 18.24 years → 18 years 2 months 25 days.
15 % return: r = 0.15 ⇒ T = 0.6931 / 0.15 ≈ 4.62 years → 4 years 7 months 14 days.
Continuous compounding is the theoretical maximum growth rate (Hull, 2022).
Rule of 72 gives only an approximation, accuracy drops below 6 % returns (Bodie et al., 2021).
FAQ
What is doubling time?
Doubling time is the period an investment needs to grow 100 % under a given compound interest rate (Investopedia, investopedia.com).
How does the calculator compute it?
It divides the natural log of 2 by your decimal return, assuming continuous reinvestment (Hull, 2022).
Why choose continuous compounding over annual or monthly?
Continuous compounding yields the shortest possible doubling time and sets a best-case benchmark (CFA Institute, 2021).
Are returns of 15 % realistic?
Historic S&P 500 annualised return is roughly 10 % before inflation (Damodaran, 2023); 15 % implies higher risk.
How does this differ from the Rule of 72?
The Rule of 72 divides 72 by the interest rate for a quick estimate but can err by 12 % at low rates (Bodie et al., 2021).
Can I shorten doubling time without extra risk?
Increase contributions, choose tax-advantaged accounts, and minimise fees; each adds effective return (SEC, investor.gov).
Does inflation change the result?
Inflation erodes real purchasing power; subtract expected inflation from return before calculating doubling time (BLS CPI FAQ).
What if the return is negative?
Negative returns make the formula undefined; the calculator flags values ≤ 0 % because capital cannot double while shrinking.
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