How to Calculate Rate of Natural Increase in Population

Use this demography calculator to determine the Rate of Natural Increase (RNI) of a population based on birth and death statistics. This tool calculates the percentage growth, net increase, and doubling time.

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How to Calculate Rate of Natural Increase

The Rate of Natural Increase (RNI) is a key demographic statistic that measures how quickly a population is growing or shrinking based solely on births and deaths, excluding the effects of migration. It is typically expressed as a percentage.

The RNI Formula

There are two common ways to calculate RNI, depending on the data you have available.

Method 1: Using Raw Numbers

RNI = [(Births – Deaths) / Total Population] × 100

This method calculates the net change (Births minus Deaths), divides it by the total population to get a decimal, and multiplies by 100 to convert it to a percentage.

Method 2: Using Crude Rates

If you already have the Crude Birth Rate (CBR) and Crude Death Rate (CDR) per 1,000 people:

RNI = (CBR – CDR) / 10

Since crude rates are "per 1,000" and RNI is a percentage ("per 100"), dividing by 10 adjusts the scale correctly.

Example Calculation

Let's look at a realistic demographic example:

• Total Population: 5,000,000
• Live Births: 120,000
• Deaths: 80,000

Step 1: Calculate Net Natural Increase
120,000 – 80,000 = 40,000 (Net Increase)

Step 2: Divide by Population
40,000 / 5,000,000 = 0.008

Step 3: Convert to Percentage
0.008 × 100 = 0.8%

So, the Rate of Natural Increase is 0.8%.

Understanding the Metrics

What is the difference between RNI and Population Growth Rate?

RNI only accounts for biology (births and deaths). Population Growth Rate includes RNI plus Net Migration (Immigration minus Emigration). A country can have a negative RNI (more deaths than births) but still grow if immigration is high.

Doubling Time (Rule of 70)

The "Rule of 70" is a way to estimate the number of years it takes for a population to double if the growth rate remains constant. You calculate it by dividing 70 by the RNI percentage.

Example: If RNI is 2.0%, the doubling time is roughly 70 / 2 = 35 years.

Note: If the RNI is negative, the population is shrinking, and the concept changes to "halving time."

High vs. Low RNI

• High RNI (> 2.0%): Often found in developing nations with high fertility rates and declining mortality rates.
• Low RNI (0% – 1.0%): Typical of industrialized nations where birth rates have stabilized near death rates.
• Negative RNI: Occurs when the death rate exceeds the birth rate, seen in some Eastern European and East Asian countries.