In demographics, the rate of natural increase (RNI) is the crude birth rate minus the crude death rate of a population. If we neglect the migration, then a positive RNI number means that the population increases and a negative number means that the population decreases.
When looking at countries, it gives an idea of what position in the Demographic Transition Model, but to find out how much a country is growing, the population growth rate should be observed.
Usually developing countries have a positive or high natural increase rate. Developed countries have a negative/neutral or low natural increase rate [1], but many developed countries have their population increasing due to immigration despite their negative RNI.
The formula for the rate of natural increase is:
The result is the rate of natural increase in percentage form.
For example, Madagascar's crude birth rate (37.89) minus the crude death rate (7.97) is 29.92; divide that by 10 and the result is 2.992%, Madagascar's rate of natural increase.
List of current RNI in world states http://hdrstats.undp.org/en/indicators/138.html