G = (b - d) * N = r * N

We just learned how to calculate the per capita rate of increase of the population ("r"), but of course, the absolute number being added to the population per unit time ("G") depends on N, the number in the population, as well.

Recall, we already developed that the population growth rate (G) over a time interval is the number of births minus the number of deaths in that interval (= B - D). (Still ignoring migration.) We can also calculate G using per capita birth and death rates (b and d) or the rate of natural increase term "r" derived previously:


We multiply (b - d) (or r; they are the same thing) by N to convert from a per capita rate to the actual number added to (or subtracted from) the population. (Remember -- don't use "r" as a percentage in this equation!)

Check yourself #4: What was "G" for the US in 2013, using the data for "N" and the per capita birth and death rates that you calculated in the section on per capita rates? ? (Click on "Answers " here to check yourself.)

Check yourself #5: Is it true that the US population would not be growing any more if it weren't for immigration? Remember that there were estimated to be about about 632,000 immigrants (net) per year into the U.S in 2013. How does your population growth rate "G" compare with immigration? (Click on Answers to check yourself.)

(Click ">>" box at the bottom to move to the next section (on percentage rates of increase) now; "<<" box to move to preceding section, "Contents" box to return to master directory for the BI301 web site. "Navigate " gives general reminders on how to do that.)