Find the most recent population of your specific group. Split this number into the sexes of the group. For example, if your group is 20- to 24-year-old people and there are 10,000 in your area, find the number of men and women and write them down separately.
Find the information on the projected births for the women in your group on your census reports. Multiply the expected births by the years that will pass during your projection period and multiple this by the projected survival rate.
Calculate the surviving number of people that will be alive in each of your groups after the period of time has passed. Multiply the number of people of that age group by the projected survival rate. Perform this for males and females because their survival rates vary. Add them up to find the total surviving people in that group.
Find the net migration rate of your area for your specific group. Subtract the people who have moved to the area on your census by the people who have moved out. Divide this result by the total population of your group and multiple it by 100. Multiple this by the number of years that pass during your projected period.
Add up your new births, your surviving population and the net migration to find the projected population of your group.