What does Rule of 70 or Doubling time mean and the formula used in it?


How you can calculate the time that will be taken by something to duplicate its size? This calculation is called the rule of 70 or Doubling time. It is simply the calculation done for the time that will be taken for something to double itself. To calculate this time you have to apply or use the rule of 70. What is the rule of 70? Rule of 70 is calculated by dividing the growth rate by 70. 

Yes, you are right, the rule of 70 is similar to the rule of 72 where the annual rate of return with 72. Bothe rules have one thing common, both formulas are the result of the very complex logarithm that is highly difficult to calculate by hand, so to simplify these rules are used. Now you must be thinking what is the difference in both, as the name of the rule says “Rule of 70 ” uses the number 70 whereas “Rule of 72” used the number 72,  both rules are completely different and are used for a different type of calculations. Rule of 70 is used only to calculate the growth that is specifically growth, it is specially used to calculate population growth whereas rule no 72 is used in finance to calculate the investments return, like how long it will take for an investment to double with fixed interest rate. Here lets only discuss the rule of 70.

The formula of Rule no 70 or doubling formula

Years to double = 7/interest rate

This is very simple to see and understand now what you have to keep in mind is that the interest rate should never be written in decimal, like if the growth rate is 18% then you must write it as 18 and not as 0.18.

You must take care that the rate matches the time frame properly as the time-frequency in which you wish to see the doubling time is relative to the growth rate frequency. For example, you want to see that how many years it would take something to double then you must use annual growth rate but if you wish to see the growths in months then use the monthly growth rate.


This formula should only be used when the specific thing or population is having an exponential growth that means that the growth of something is increasing at a rapid constant rate compared to a current quantity like take the example of the population if the growth of population was experiencing very less or sporadic growth rate then you should not use this formula there. If the growth rate increases then, as a result, it is obvious that the doubling time will be fast and it will take lesser time to reach the doubled quantity. Now, for example, it is obvious that if you increase the number of seeds to be plated and plan accordingly then you will definitely see more plants grown. Now the knowledge is different from everything and depends on the outside influences, organisms larger in size have slow growth as because of more cells the have for example giraffe will take more time then rabbits. So the growth rate of the rabbit is higher than the giraffe’s growth rate.  What is logistic growth? it is when a group reaches its capacity you will see a decline in population that’s logistic growth, doubling time will not be applicable here but still, you can include them in estimation.



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