Determine the initial population of the group you are studying.
Determine the population of the group one time period later. The unit of time can be any measure of time depending on what you are studying. For example, if you are studying bacteria that reproduce rapidly, you might be able to see change in an hour; if you are studying the population of the world, it would be better to use years
Calculate the percentage change in population from the start of the time period to one unit of time later by dividing ending population by the initial population. For example, if you were studying bacteria and started out with 1 and after one hour you had 2, you would get 2, or a 100 percent growth rate.
Calculate the change in population several time periods later. For example, if you were studying bacteria you might note the change from hour nine to hour 10 went from 512 to 1,024 bacteria. By dividing 1,024 by 512, you would get 2, or the same 100 percent growth rate.
Determine the change in the growth rate from the first time period to the second time period. If the growth rate remains the same, you have an exponential growth rate. If the growth rate decreases, you have a logistic growth rate. For example, since the population of the bacteria continued to grow at a 100 percent rate, the growth was exponential. However, if you had observed a change from 400 to 600 during the second time frame, the growth rate would have only been 1.5, or 50 percent, meaning that the growth rate was decreasing and the growth was logistic.