function calculateRetention() {
var startEmp = document.getElementById('startEmployees').value;
var endEmp = document.getElementById('endEmployees').value;
var newHires = document.getElementById('newHires').value;
var errorDiv = document.getElementById('errorMsg');
var resultDiv = document.getElementById('resultBox');
// Reset UI
errorDiv.style.display = 'none';
resultDiv.style.display = 'none';
errorDiv.innerText = ";
// Validation
if (startEmp === " || endEmp === " || newHires === ") {
errorDiv.innerText = 'Please fill in all fields.';
errorDiv.style.display = 'block';
return;
}
var S = parseFloat(startEmp);
var E = parseFloat(endEmp);
var N = parseFloat(newHires);
if (S <= 0) {
errorDiv.innerText = 'Employees at start must be greater than 0.';
errorDiv.style.display = 'block';
return;
}
if (N < 0 || E < 0) {
errorDiv.innerText = 'Values cannot be negative.';
errorDiv.style.display = 'block';
return;
}
// Calculation Logic
// Retention Formula: ((End Count – New Hires) / Start Count) * 100
// 1. Calculate how many from the original start group remain
var retained = E – N;
// Logic Check: Retained cannot be more than start (unless data error)
// Logic Check: Retained cannot be negative (implies more new hires than total end count)
if (retained S) {
errorDiv.innerText = 'Error: Retained employees cannot exceed starting employees. Check your inputs.';
errorDiv.style.display = 'block';
return;
}
// 2. Calculate separated (Start – Retained)
var separated = S – retained;
// 3. Calculate Rate
var rate = (retained / S) * 100;
// Output Results
document.getElementById('resRetained').innerText = retained;
document.getElementById('resSeparated').innerText = separated;
document.getElementById('resRate').innerText = rate.toFixed(2) + '%';
resultDiv.style.display = 'block';
}
How is Employee Retention Rate Calculated?
Employee retention rate is a critical human resources metric that measures the percentage of employees who remain with an organization over a specific period. It helps companies understand their ability to keep talent and maintain stability within the workforce. A high retention rate generally indicates a positive work environment, while a low rate may signal underlying issues with management, compensation, or company culture.
The Retention Rate Formula
To calculate the retention rate accurately, you must exclude new hires who joined during the period. The goal is to track the retention of the staff that existed on the first day of that period.
Retention Rate = ( ( Total Employees at End – New Hires ) / Total Employees at Start ) × 100
Here is a breakdown of the variables:
Total Employees at Start: The headcount on the very first day of the measurement period (e.g., January 1st).
Total Employees at End: The headcount on the last day of the measurement period (e.g., December 31st).
New Hires: The number of employees hired specifically between the start and end dates.
Calculation Example
Let's assume you want to calculate the annual retention rate for your department based on the following data:
Employees on January 1st: 50
Employees on December 31st: 48
New employees hired during the year: 4
Step 1: Determine Retained Employees
Subtract new hires from the end count to see how many original employees stayed. 48 (End) – 4 (New) = 44 (Retained)
Step 2: Apply the Formula
Divide the retained employees by the starting count and multiply by 100. (44 / 50) × 100 = 88%
In this example, the employee retention rate is 88%.
Retention vs. Turnover
While retention rate measures those who stay, turnover rate measures those who leave. They are two sides of the same coin but are calculated differently. Turnover often uses the average number of employees during the period as the denominator, whereas retention strictly uses the starting headcount.
Why Monitor This Metric?
Tracking retention helps businesses estimate recruitment costs, assess the impact of culture initiatives, and identify trends in workforce stability. Consistently monitoring this rate on a quarterly or annual basis allows HR leadership to intervene early if retention begins to drop.