.pop-calc-wrapper {
max-width: 700px;
margin: 20px auto;
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
background: #ffffff;
border: 1px solid #e0e0e0;
border-radius: 8px;
box-shadow: 0 4px 12px rgba(0,0,0,0.05);
padding: 30px;
}
.pop-calc-header {
text-align: center;
margin-bottom: 25px;
border-bottom: 2px solid #f0f0f0;
padding-bottom: 15px;
}
.pop-calc-header h2 {
color: #2c3e50;
margin: 0;
font-size: 24px;
}
.pop-input-group {
margin-bottom: 20px;
}
.pop-input-group label {
display: block;
font-weight: 600;
color: #555;
margin-bottom: 8px;
}
.pop-input-group input {
width: 100%;
padding: 12px;
border: 1px solid #ddd;
border-radius: 4px;
font-size: 16px;
transition: border-color 0.3s;
box-sizing: border-box;
}
.pop-input-group input:focus {
border-color: #3498db;
outline: none;
}
.pop-calc-btn {
width: 100%;
padding: 14px;
background-color: #3498db;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.pop-calc-btn:hover {
background-color: #2980b9;
}
.pop-results {
margin-top: 30px;
background-color: #f8f9fa;
padding: 20px;
border-radius: 6px;
display: none;
border-left: 5px solid #27ae60;
}
.pop-result-row {
display: flex;
justify-content: space-between;
margin-bottom: 12px;
border-bottom: 1px solid #eee;
padding-bottom: 8px;
}
.pop-result-row:last-child {
border-bottom: none;
margin-bottom: 0;
padding-bottom: 0;
}
.pop-result-label {
color: #666;
font-size: 15px;
}
.pop-result-value {
font-weight: bold;
color: #2c3e50;
font-size: 18px;
}
.pop-error {
color: #e74c3c;
text-align: center;
margin-top: 10px;
display: none;
}
.pop-article {
max-width: 700px;
margin: 40px auto;
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
line-height: 1.6;
color: #333;
}
.pop-article h2 {
color: #2c3e50;
border-bottom: 1px solid #eee;
padding-bottom: 10px;
margin-top: 30px;
}
.pop-article h3 {
color: #34495e;
margin-top: 25px;
}
.pop-article p {
margin-bottom: 15px;
}
.pop-article ul {
margin-bottom: 15px;
padding-left: 20px;
}
.pop-article li {
margin-bottom: 8px;
}
.formula-box {
background: #f1f8ff;
padding: 15px;
border-radius: 4px;
font-family: monospace;
text-align: center;
margin: 20px 0;
border: 1px dashed #3498db;
}
function calculatePopulation() {
// Input Retrieval
var initialPopInput = document.getElementById('initialPop');
var growthRateInput = document.getElementById('growthRate');
var timePeriodInput = document.getElementById('timePeriod');
var errorDiv = document.getElementById('popError');
var resultsDiv = document.getElementById('popResults');
// Parse Values
var P0 = parseFloat(initialPopInput.value);
var r = parseFloat(growthRateInput.value);
var t = parseFloat(timePeriodInput.value);
// Reset Display
errorDiv.style.display = 'none';
resultsDiv.style.display = 'none';
// Validation
if (isNaN(P0) || isNaN(r) || isNaN(t) || P0 < 0 || t 0) {
totalPercentChange = ((finalPopulation – P0) / P0) * 100;
}
// Output Formatting
document.getElementById('futurePopVal').innerText = finalPopulation.toLocaleString();
var changeSign = totalChange >= 0 ? "+" : "";
document.getElementById('popChangeVal').innerText = changeSign + totalChange.toLocaleString();
document.getElementById('percentChangeVal').innerText = changeSign + totalPercentChange.toFixed(2) + "%";
// Show Results
resultsDiv.style.display = 'block';
}
How to Calculate Population Size with Growth Rate
Understanding how populations change over time is essential for urban planning, biology, ecology, and resource management. Whether you are projecting the growth of a city, a colony of bacteria, or a specific demographic group, the fundamental mathematics remains consistent.
The Exponential Growth Formula
To calculate the future size of a population assuming a constant growth rate, we use the Exponential Growth Model. This model assumes that the growth rate is proportional to the current population size, leading to compounding growth (or decay).
P(t) = P₀ × (1 + r)ᵗ
Where:
- P(t): The Future Population at time t.
- P₀: The Initial (Current) Population size.
- r: The growth rate expressed as a decimal (e.g., 2% becomes 0.02).
- t: The time period (usually in years) over which the population grows.
Example Calculation
Let's look at a realistic scenario using the formula above.
Imagine a small town with a current population of 10,000 people. The town is growing at an annual rate of 3%. We want to know the population size in 5 years.
- Initial Population (P₀) = 10,000
- Rate (r) = 3% = 0.03
- Time (t) = 5 years
Step 1: Add 1 to the rate: 1 + 0.03 = 1.03.
Step 2: Raise this to the power of the time period: 1.03⁵ ≈ 1.1593.
Step 3: Multiply by the initial population: 10,000 × 1.1593 ≈ 11,593.
After 5 years, the town's population would be approximately 11,593.
Interpreting the Growth Rate
The input variable for "Growth Rate" dictates the trajectory of the population:
- Positive Rate (r > 0): The population is increasing.
- Zero Rate (r = 0): The population remains stable (Zero Population Growth).
- Negative Rate (r < 0): The population is shrinking. In the calculator above, you can enter a negative value (e.g., -1.5) to simulate population decline.
Limitations of the Model
While this calculator provides a mathematical projection based on exponential growth, real-world populations often face constraints. In biology, this is known as the "carrying capacity"—the maximum population size an environment can sustain. As populations approach this limit, growth often slows, following a logistic growth curve rather than a purely exponential one. However, for short-term human demographic projections or initial biological estimates, the exponential formula is the standard tool.