The Net Reproduction Rate is defined as the average number of females born to a woman taking into consideration the mortality of the mothers.

The Net Reproduction Rate measures the extent to which mothers produce female infants who survive to replace them.

It measures the extent to which a generation of girl babies survive and in turn give birth as they pass through the child-bearing age group.

We need to include mortality because it might happen that a woman dies before her child-bearing age is completed.

If the net reproduction rate is 1 it means that a group of newborn girls will exactly replace itself in the new generation. Thus in this case the population has a tendency to more or less remain constant.

If the rate is greater than 1 then the population has a tendency to increase and if the rate is less than 1 the population has a tendency to decrease.

The Net Reproduction Rate usually ranges from 0 to 5 per annum.

**Formula:**

Suppose that the child-bearing age of a woman lies between the ages x and x+n. The probability of survival of a female between the age interval x and x+n is called the survival rate.

If we know the survival rate then the net reproduction rate can be calculated using the formula,

Net Reproduction Rate = ∑[n * Female Age-Specific Mortality at Age i * Survival Rate].

Here the sum over i is taken over all ages in the reproductive span, that is, from i=x to i=x+n.