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How many years does it take beforeyour investment doubles in value? If we assume the investmentis compounding continuously, then we can start with the followingformula:A= P e rtwhereA is theaccumulated value, Pis principal, ris the annual interest rate and tis time in years.

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A doubling of the principal means thatA = 2 Pand the formula would become:2 P= P e rt2 = e rt, ln 2 = rt,t = ln 2/ rIf wemultiply the top and bottom by 100, the previous equation can bere-written as:t= 100 ln 2 / 100 r= 70 / 100 r= 70 / annual interest ratesince100 ln 2 70 and ris the annual interest as a decimal, 100 ris the annual inflation as a percent. The above formula is oftencalled the Rule of 70. Let's consider some examples.Example 1Assume that the annual rate of inflation is 2.5%. Estimate thenumber of years it takes for prices to double.t= 70 / 2.5 = 28 yearsIttakes roughly 28 years for prices to double at an annual inflationrate of 2.5%.Example 2You invest your savings account at 8% annual interest. Howlong does it take before that original investment will double invalue using the Rule of 70?t= 70 / 8.0 = 8.75 9 yearsThe online calculator below determines thetime (in years) that it takes before your investment will double invalue.

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Change the annualinterest rate to the right and then click Calculate.Rule of 70Annual Interest Rate%YearsWe ask that if you like this software,that you add one of the following links to your website:Generate fixed, variable orinterest-only amortization schedules.Trackloans with ease. Add, edit, or delete to manage irregular payments.RELATED LINKS.