Calculate blended overtime rates based on weighted averages.
The extra amount paid per hour for the shift (e.g., Night Shift Premium).
How many of the Total Hours were worked during the differential period?
Base Earnings (No Diff):–
Differential Pay (Premium):–
Total Straight-Time Pay:–
Regular Rate of Pay (Weighted):–
Overtime Hours (Over 40):–
Overtime Premium (0.5x Regular Rate):–
Total Gross Pay:–
function calculateShiftOvertime() {
// Clear previous errors
var errorDiv = document.getElementById('errorMessage');
errorDiv.style.display = 'none';
errorDiv.innerText = ";
document.getElementById('result-container').style.display = 'none';
// Get Inputs
var baseRate = parseFloat(document.getElementById('baseRate').value);
var diffRate = parseFloat(document.getElementById('diffRate').value);
var totalHours = parseFloat(document.getElementById('totalHours').value);
var diffHours = parseFloat(document.getElementById('diffHours').value);
// Validation
if (isNaN(baseRate) || isNaN(diffRate) || isNaN(totalHours) || isNaN(diffHours)) {
errorDiv.innerText = "Please fill in all fields with valid numbers.";
errorDiv.style.display = 'block';
return;
}
if (diffHours > totalHours) {
errorDiv.innerText = "Differential hours cannot exceed Total hours.";
errorDiv.style.display = 'block';
return;
}
if (totalHours < 0 || baseRate < 0 || diffHours 0) {
regularRate = totalStraightTime / totalHours;
}
// 3. Calculate Overtime
var overtimeThreshold = 40;
var otHours = 0;
var otPremiumPay = 0;
if (totalHours > overtimeThreshold) {
otHours = totalHours – overtimeThreshold;
// Under FLSA, because straight time is already calculated for all hours (including OT hours) in step 1,
// the OT premium is 0.5 * Regular Rate for the OT hours.
// Formula: (Total Straight Time) + (OT Hours * 0.5 * Regular Rate)
otPremiumPay = otHours * (regularRate * 0.5);
}
var totalPay = totalStraightTime + otPremiumPay;
// Display Results
document.getElementById('resBaseEarnings').innerText = "$" + baseEarnings.toFixed(2);
document.getElementById('resDiffEarnings').innerText = "$" + diffEarnings.toFixed(2);
document.getElementById('resStraightTime').innerText = "$" + totalStraightTime.toFixed(2);
document.getElementById('resRegularRate').innerText = "$" + regularRate.toFixed(2) + " /hr";
document.getElementById('resOTHours').innerText = otHours.toFixed(2);
document.getElementById('resOTPremium').innerText = "$" + otPremiumPay.toFixed(2);
document.getElementById('resTotalPay').innerText = "$" + totalPay.toFixed(2);
document.getElementById('result-container').style.display = 'block';
}
How to Calculate Overtime Rates for Shift Differentials
Calculating overtime pay becomes complex when an employee works different shifts with varying pay rates within a single workweek. This is common in healthcare, manufacturing, and security sectors where "shift differentials" are paid for nights, weekends, or undesirable shifts.
When a shift differential is involved, you cannot simply multiply the base hourly rate by 1.5. Instead, you must calculate the Regular Rate of Pay, which is a weighted average of all hourly rates earned during that week.
The "Regular Rate" Formula
According to FLSA (Fair Labor Standards Act) regulations, overtime must be paid at 1.5 times the "Regular Rate," not just the base rate. Here is the step-by-step logic used in the calculator above:
Calculate Total Straight-Time Pay: multiply all hours worked by the base rate, then add the total shift differential amount earned (Differential Rate × Differential Hours).
Determine the Regular Rate: Divide the Total Straight-Time Pay by the Total Hours worked. This gives you the "blended" hourly rate.
Calculate Overtime Premium: Since the straight-time pay (the "1" in 1.5) was already covered in step 1 for all hours, you owe the employee an extra 0.5 times the Regular Rate for every hour worked over 40.
Total Gross Pay: Add the Total Straight-Time Pay and the Overtime Premium.
Example Calculation
Let's look at a realistic scenario to illustrate how this works mathematically:
Employers sometimes mistakenly calculate overtime based on the rate in effect when the overtime hours occurred, or simply use the base rate. Using the base rate underpays the employee and violates labor laws. Using the weighted average method ensures fair compensation that reflects the actual earnings profile of the week.
Common Shift Differential Scenarios
Second/Third Shift: A flat dollar amount added per hour (e.g., $1.50/hr).
Weekend Pay: A higher base rate or differential for Saturday/Sunday work.
Hazard Pay: Additional hourly pay for dangerous working conditions.
In all these cases, the extra earnings must be included in the total straight-time pay before determining the overtime rate.