Doubling Time

Pronunciation: /ˈdʌ blɪŋ taɪm/ ?

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Manipulative 1: Doubling Time. Created with GeoGebra.

Doubling time is the amount of time it takes for an exponential function to double. If an exponential function goes from 1 to 2 in 10 seconds, it will go from 2 to 4 in 10 seconds and 4 to 8 in 10 seconds. An exponential function always doubles in the same amount of time.

Manipulative 1 illustrates doubling time for an exponential function of the form
Click on the blue points on the sliders and drag them to change the equation for the graph.


  1. How does the doubling time change when a changes? Why?
  2. How does the doubling time change when b changes? Why?

Rule of 72

The rule of 72 can be used to approximate doubling time of investments at a given interest rate. The rule of 72 states:
where r is the interest rate.


  1. Rule of 72. Investopedia. Forbes Digital. (Accessed: 2010-01-05).
  2. Lodge, Sir Oliver. Easy Mathematics; or, Arithmetic and Algebra for General Readers, pp 353-356. Macmillan and Company, 1910. (Accessed: 2010-01-24).
  3. Math 120 Book, pp 698-699. (Accessed: 2010-01-24).

Cite this article as:

Doubling Time. 2010-01-24. All Math Words Encyclopedia. Life is a Story Problem LLC.


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Revision History

2008-12-16: Initial version (McAdams, David.)

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