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In finance, the rule of 72, the rule of 70 [1] and the rule of 69.3 are methods for estimating an investment's doubling time. The rule number (e.g., 72) is divided by the interest percentage per period (usually years) to obtain the approximate number of periods required for doubling.
For continuous compounding interest, you’ll get more accurate results by using 69.3 instead of 72. The Rule of 72 is an estimate, and 69.3 is harder for mental math than 72, which divides easily ...
Using the Rule of 72, your money should double every 10.3 years. So, by age 45, you should have around $200,000 in retirement savings. By age 55, you should have around $400,000.
This "Rule of 70" gives accurate doubling times to within 10% for growth rates less than 25% and within 20% for rates less than 60%. Larger growth rates result in the rule underestimating the doubling time by a larger margin. Some doubling times calculated with this formula are shown in this table. Simple doubling time formula:
The Summa de arithmetica of Luca Pacioli (1494) gives the Rule of 72, stating that to find the number of years for an investment at compound interest to double, one should divide the interest rate into 72. Richard Witt's book Arithmeticall Questions, published in 1613, was a landmark in the history of compound interest.
Continue reading → The post What Is the Rule of 72? appeared first on SmartAsset Blog. For many, predicting how your investments will perform over the long term can be difficult. After all ...
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The assumption of constant investment opportunities can be relaxed. This requires a model for how ,, change over time. An interest rate model could be added and would lead to a portfolio containing bonds of different maturities. Some authors have added a stochastic volatility model of stock market returns.