Infant mortality rate is the probability of a child born in a specific year or period dying before reaching the age of one, if subject to age-specific mortality rates of that period. It is an important indicator of the overall physical health of a society and reflects the social, economic, and environmental conditions in which children live, including their health care. The infant mortality rate is calculated by dividing the number of infant deaths by the number of live births and multiplying the result by 1000. The formula for calculating the infant mortality rate is as follows:

Infant Mortality Rate (IMR) = (Number of Infant Deaths / Number of Live Births) x 1000

The IMR is expressed as the number of deaths of children under one year of age per 1000 live births. High IMR indicates poor health conditions in the country along with other requirements that play a vital role in developing the good health of the child. The infant mortality rate is one of the three factors of physical quality of life to measure economic development and indicates population health. In 2021, the infant mortality rate in the United States was 5.4 deaths per 1,000 live births.