The total fertility rate (TFR) of a population is the average number of children that would be born to a female over their lifetime if: they were to experience the exact current age-specific fertility rates (ASFRs) through their lifetime they were to live from birth until the end of their reproductive life. It is obtained by summing the single-year age-specific rates at a given time. , the total fertility rate varied widely across the world, from 0.78 in South Korea to 6.73 in Niger. Fertility tends to be correlated with levels of economic development. Historically, developed countries have significantly lower fertility rates, generally correlated with greater wealth, education, urbanization, and other factors. Conversely, in least developed countries, fertility rates tend to be higher. Families desire children for their labor and as caregivers for their parents in old age. Fertility rates are also higher due to the lack of access to contraceptives, stricter adherence to religious beliefs, generally lower levels of female education, and lower rates of female employment. As of 2020, the total fertility rate for the world is 2.3. The global TFR has declined rapidly since the 1960s, and some forecasters like Sanjeev Sanyal argue that the effective global fertility rate will fall below global replacement rate, estimated to be 2.3, in the 2020s. This would stabilize world population sometime during the period 2050–2070. The United Nations predicts that global fertility will continue to decline for the remainder of this century and reach a below-replacement level of 1.8 by 2100, and that world population will peak during the period 2084-2088. Taken together, these projections indicate that the human population will achieve zero growth sometime in the second half of this century. The TFR is not based on the fertility of any real group of women since this would involve waiting until they had completed childbearing. Nor is it based on counting up the total number of children actually born over their lifetime.