Net Reproduction Rate Calculation Formula

Calculate population replacement potential based on fertility and mortality rates.

Average number of children born to a woman over her lifetime.

Standard demographic estimate is approx. 48.8%.

Probability of a female newborn surviving to the mean age of childbearing.

What is Net Reproduction Rate (NRR)?

The Net Reproduction Rate (NRR) is a key demographic metric used to determine if a population can replace itself from one generation to the next. Unlike the Gross Reproduction Rate (GRR), which assumes all females survive to the end of their childbearing years, the NRR accounts for mortality.

It represents the average number of daughters a hypothetical cohort of newborn daughters would have during their lifetimes if they were subject to the current age-specific fertility and mortality rates.

The NRR Formula

While the precise calculation involves summing age-specific fertility rates multiplied by age-specific survival rates, a simplified formula for estimation is:

NRR ≈ TFR × (% Female Births) × (Survival Probability)

Where:

• TFR (Total Fertility Rate): The average number of children a woman would have in her lifetime.
• % Female Births: The proportion of births that are girls (usually around 48.8% or 0.488).
• Survival Probability: The likelihood of a female surviving from birth to the mean age of reproduction.

Interpreting the Results

The Net Reproduction Rate provides a clear snapshot of potential population growth:

NRR = 1 (Replacement Level)

If the NRR is exactly 1.0, each generation of mothers is having exactly enough daughters to replace themselves in the population. The population is considered stable in the long run.

NRR < 1 (Sub-Replacement Fertility)

If the NRR is less than 1.0, the population is not replacing itself. Each generation is smaller than the previous one, leading to an eventual population decline unless compensated by immigration.

NRR > 1 (Population Growth)

If the NRR is greater than 1.0, each mother is being replaced by more than one daughter on average. This indicates the population will grow over subsequent generations.

Why Mortality Matters

In developed countries with high healthcare standards, the NRR is often very close to the Gross Reproduction Rate (GRR) because almost all women survive to reproductive age. However, in regions with higher mortality rates, the gap between GRR and NRR widens significantly. A high fertility rate does not guarantee population growth if the survival rate to adulthood is low.