According to the Organisation for Economic Co-operation and Development, the rate of natural increase represents the difference between the crude birth rate and crude death rate. This statistic excludes effects of migration.
The rate of natural increase measures the difference between live births and deaths in a year, divided by the mid-year population and multiplied by a particular factor. It measures the difference between the crude birth rate, or number of live births per year per 1000 population, and the crude death rate, or number of deaths per year per 1000 population. It is commonly expressed as a percent. As of 2013, the rate of natural increase in the United States is 0.5 percent as per the Population Reference Bureau.