In demography and population dynamics, the rate of natural increase (RNI), also known as natural population change, is defined as the birth rate minus the death rate of a particular population, over a particular time period. It is typically expressed either as a number per 1,000 individuals in the population or as a percentage. RNI can be either positive or negative. It contrasts to total population change by ignoring net migration.

This RNI gives demographers an insight into how a region's population is evolving, and these analyses can inform government attempts to shape RNI.

Suppose a population of 5,000 individuals experiences 1,150 live births and 900 deaths over the course of one year.

To show the RNI over that year as a percentage, the equation would be

           (1,150 – 900) ÷ 5,000 = 0.05 = +5%

To show the RNI as a number per 1,000 individuals in the population, the equation would be

           (1,150 – 900) ÷ (5,000/1,000) = 250 ÷ 5 = +50

It can also be shown as natural births per 1,000 minus deaths per 1,000