365 Days (Standard)
366 Days (Leap Year)
360 Days (Accounting Standard)
Days Worked / Eligible:0
Proration Percentage:0%
Calculated Pro Rata Bonus:$0.00
function calculateProRataBonus() {
// 1. Get input values
var fullBonusInput = document.getElementById("fullBonus").value;
var startDateInput = document.getElementById("startDate").value;
var endDateInput = document.getElementById("endDate").value;
var basisDaysInput = document.getElementById("basisDays").value;
// 2. Validate inputs
var errorDiv = document.getElementById("errorMsg");
var resultDiv = document.getElementById("resultBox");
errorDiv.style.display = "none";
resultDiv.style.display = "none";
if (fullBonusInput === "" || startDateInput === "" || endDateInput === "") {
errorDiv.innerHTML = "Please fill in all fields correctly.";
errorDiv.style.display = "block";
return;
}
var fullBonus = parseFloat(fullBonusInput);
var basis = parseInt(basisDaysInput);
// 3. Date Logic
// Create date objects set to midnight to ensure accurate day calculation
var start = new Date(startDateInput);
var end = new Date(endDateInput);
// Check for valid dates
if (isNaN(start.getTime()) || isNaN(end.getTime())) {
errorDiv.innerHTML = "Invalid date format.";
errorDiv.style.display = "block";
return;
}
// Check if start date is after end date
if (start > end) {
errorDiv.innerHTML = "Start date cannot be after the End date.";
errorDiv.style.display = "block";
return;
}
// 4. Calculate Days Difference
// Difference in milliseconds
var diffTime = Math.abs(end – start);
// Convert to days (divide by 1000ms * 60s * 60m * 24h)
// Add 1 to include both the start date and end date in the count
var daysWorked = Math.ceil(diffTime / (1000 * 60 * 60 * 24)) + 1;
// 5. Calculate Pro Rata Logic
var percentage = (daysWorked / basis) * 100;
// Cap at 100% if they somehow worked more than the basis (unlikely but safe)
if (percentage > 100) percentage = 100;
var calculatedBonus = (fullBonus * percentage) / 100;
// 6. Formatting Results
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById("resDays").innerHTML = daysWorked + " days";
document.getElementById("resPercent").innerHTML = percentage.toFixed(2) + "%";
document.getElementById("resBonus").innerHTML = formatter.format(calculatedBonus);
// 7. Display Result
resultDiv.style.display = "block";
}
How to Calculate Bonus Pro Rata
Calculating a pro rata bonus is an essential task for HR professionals, payroll managers, and employees who join or leave a company in the middle of a fiscal year. A "pro rata" (proportional) bonus ensures that an employee is compensated fairly based on the exact amount of time they contributed to the organization during the performance period, rather than receiving a full year's bonus or no bonus at all.
What is a Pro Rata Bonus?
A pro rata bonus is a portion of a target annual bonus calculated in proportion to the time an employee was employed or eligible during the bonus period. For example, if an employee is hired halfway through the year, they are typically entitled to 50% of the full annual bonus target.
The Pro Rata Bonus Formula
The most accurate way to calculate a pro rata bonus is by using the number of days employed. While some organizations calculate by months, using days avoids discrepancies regarding months with different lengths (e.g., February vs. August).
Step 1: Determine Total Eligible Days
Calculate the number of days the employee worked during the bonus period. This is done by subtracting the start date from the end date and adding 1 (to include the first day).
Formula: (End Date – Start Date) + 1 = Days Worked
Step 2: Calculate the Proration Factor
Divide the days worked by the total number of days in the year (usually 365, or 366 for leap years).
Formula: Days Worked ÷ 365 = Proration Percentage
Step 3: Apply to Target Bonus
Multiply the full target bonus amount by the proration percentage.
Formula: Full Bonus × Proration Percentage = Final Pro Rata Bonus
Calculation Example
Imagine an employee named Sarah. Her employment contract states she is eligible for a $10,000 annual bonus. She joined the company on July 1st and the fiscal year ends on December 31st.
Full Bonus Target: $10,000
Period: July 1 to December 31
Days Worked: 184 days
Total Year Days: 365 days
Calculation: (184 ÷ 365) = 0.5041 (or 50.41%)
Final Bonus: $10,000 × 0.5041 = $5,041.10
Why Use a Pro Rata Calculator?
Using a calculator reduces human error. Manual date counting is prone to mistakes, particularly when crossing months with varying days or handling leap years. This tool ensures that both employers and employees have a transparent, accurate figure for compensation discussions.