The "Rule of 70" is a simple formula used to estimate the time it takes for an investment or population to double in size. By dividing 70 by the annual growth rate (expressed as a percentage), you can quickly find the approximate number of years needed for doubling. For example, if an investment grows at a rate of 5% per year, it will take about 14 years to double (70 ÷ 5 = 14). This rule is commonly applied in finance and economics, particularly when analyzing the growth of investments, savings, or population. While it provides a useful estimate, it is important to remember that actual growth rates can fluctuate, affecting the time required for doubling.