*Note: This calculation excludes migration (immigration/emigration).
function calculateRNI() {
// Get input values
var births = document.getElementById('totalBirths').value;
var deaths = document.getElementById('totalDeaths').value;
var population = document.getElementById('totalPopulation').value;
// Convert to numbers
var b = parseFloat(births);
var d = parseFloat(deaths);
var p = parseFloat(population);
// Validation
if (isNaN(b) || isNaN(d) || isNaN(p) || p 0) {
var dt = 70 / rni;
doublingTimeText = dt.toFixed(1) + " Years";
} else if (rni === 0) {
doublingTimeText = "Infinite (Stable)";
}
// Display Results
document.getElementById('rniOutput').innerText = rni.toFixed(2) + "%";
document.getElementById('cbrOutput').innerText = cbr.toFixed(1) + " per 1,000″;
document.getElementById('cdrOutput').innerText = cdr.toFixed(1) + " per 1,000″;
document.getElementById('netChangeOutput').innerText = netChange.toLocaleString();
document.getElementById('doublingTimeOutput').innerText = doublingTimeText;
// Show result container
document.getElementById('rniResults').style.display = 'block';
}
How is Rate of Natural Increase Calculated?
The Rate of Natural Increase (RNI) is a critical demographic statistic used to understand how a population is changing based solely on births and deaths, excluding the effects of migration. It tells us whether a population is expanding or shrinking naturally.
The Formula
There are two common ways to calculate the Rate of Natural Increase, depending on the data you have available. Both methods yield the same percentage result.
Method 1: Using Raw Data
If you have the total number of live births, total deaths, and the total population size:
RNI (%) = [ (Births – Deaths) / Total Population ] × 100
Method 2: Using Demographic Rates
Demographers often use the Crude Birth Rate (CBR) and Crude Death Rate (CDR), which represent the number of births or deaths per 1,000 people.
RNI (%) = (CBR – CDR) / 10
Note: We divide by 10 because CBR and CDR are per 1,000, while RNI is expressed as a percentage (per 100).
Key Definitions
Crude Birth Rate (CBR): The number of live births per 1,000 people in the population per year.
Crude Death Rate (CDR): The number of deaths per 1,000 people in the population per year.
Zero Population Growth: Occurs when the RNI is 0% (Births = Deaths).
Doubling Time: An estimate of how many years it will take for the population to double in size at the current growth rate, calculated using the "Rule of 70" (70 divided by the RNI percentage).
RNI vs. Population Growth Rate
It is important to distinguish between RNI and the overall Population Growth Rate. The RNI only accounts for biological factors (births and deaths). The Population Growth Rate accounts for RNI plus Net Migration (Immigration minus Emigration).
For example, a country might have a negative RNI (more deaths than births) but still grow in population if it has high levels of immigration.
Interpreting the Results
High RNI (> 2%): Indicates a rapidly growing population, often seen in developing nations with high fertility rates and declining death rates.
Moderate RNI (1% – 2%): Indicates steady growth.
Low RNI (< 1%): Indicates slow growth, typical of developed industrialized nations.
Negative RNI: Indicates a natural population decline (more deaths than births).