Zero population growth, sometimes abbreviated ZPG, is a condition of demographic balance where the number of people in a specified population neither grows nor declines; that is, the number of births plus in-migrants equals the number of deaths plus out-migrants. The Zero Population Growth organization, founded by biologist Paul R. Ehrlich, induced a prominent political movement since the 1960s, aiming to reach zero population growth.

The movement considers zero population growth to be an objective towards which countries and the whole world should strive in the interests of accomplishing long-term optimal standards and conditions of living. It faces substantial support as well as criticism, involving different groups of people in society.

The growth rate of a population in a given year equals the number of births minus the number of deaths plus immigration minus emigration expressed as a percentage of the population at the beginning of the given year.

For example, suppose a country begins a year with one million people and during the year experiences one hundred thousand births, eighty thousand deaths, one thousand immigrants and two hundred emigrants.

          Change in population = 100,000 – 80,000 +1,000 – 200 = 20,800

          Population growth rate = (20,800 ÷ 1,000,000) x 100% = 2.1%

Zero population growth for a country occurs when the sum of these four numbers – births minus deaths plus immigration minus emigration - is zero.

To illustrate, suppose a country begins the year with one million people and during the year experiences 85,000 births, 86,000 deaths, 1,500 immigrants and 500 emigrants.