Population momentum

Population momentum is when a group of people, like a city or country, keeps growing even after the number of births and deaths each year are equal. This happens because even when the number of babies born and the number of people dying are the same, the group will have more people. That's because there are usually more people in their teenage years and young adult years who can have babies than there are old people who have already had kids. So even when the same number of people are born and die each year, the group will get bigger because all the young people who can have babies are adding to the population.