function calculateProratedBonus() {
// Clear previous results and errors
document.getElementById('resultBox').style.display = 'none';
document.getElementById('errorMsg').style.display = 'none';
// Get Inputs
var totalBonus = parseFloat(document.getElementById('totalBonus').value);
var periodStartStr = document.getElementById('periodStart').value;
var periodEndStr = document.getElementById('periodEnd').value;
var workStartStr = document.getElementById('workStart').value;
var workEndStr = document.getElementById('workEnd').value;
// Validation
if (isNaN(totalBonus) || totalBonus < 0) {
showError("Please enter a valid bonus amount.");
return;
}
if (!periodStartStr || !periodEndStr || !workStartStr || !workEndStr) {
showError("Please select all date fields.");
return;
}
// Parse Dates (set time to noon to avoid timezone shift issues on day diff calculation)
var pStart = new Date(periodStartStr + 'T12:00:00');
var pEnd = new Date(periodEndStr + 'T12:00:00');
var wStart = new Date(workStartStr + 'T12:00:00');
var wEnd = new Date(workEndStr + 'T12:00:00');
// Logic Validation
if (pEnd < pStart) {
showError("Bonus Period End Date cannot be before Start Date.");
return;
}
if (wEnd < wStart) {
showError("Employment End Date cannot be before Start Date.");
return;
}
// Calculate Total Days in Bonus Period (Inclusive)
var oneDay = 24 * 60 * 60 * 1000;
var totalDays = Math.round((pEnd – pStart) / oneDay) + 1;
if (totalDays wStart) ? pStart : wStart;
var overlapEnd = (pEnd < wEnd) ? pEnd : wEnd;
var eligibleDays = 0;
// If there is an actual overlap
if (overlapStart <= overlapEnd) {
eligibleDays = Math.round((overlapEnd – overlapStart) / oneDay) + 1;
}
// Calculate Percentage and Amount
var percentage = (eligibleDays / totalDays) * 100;
var proratedAmount = totalBonus * (percentage / 100);
// Display Results
document.getElementById('totalDaysDisplay').innerText = totalDays;
document.getElementById('eligibleDaysDisplay').innerText = eligibleDays;
document.getElementById('percentDisplay').innerText = percentage.toFixed(2) + "%";
// Format Currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById('finalBonusDisplay').innerText = formatter.format(proratedAmount);
document.getElementById('resultBox').style.display = 'block';
}
function showError(msg) {
var errDiv = document.getElementById('errorMsg');
errDiv.innerText = msg;
errDiv.style.display = 'block';
}
Understanding Bonus Proration
A prorated bonus is a partial bonus payment calculated based on the specific amount of time an employee was active or eligible during a company's fiscal bonus period. This calculation is essential for HR professionals, payroll managers, and employees who join or leave a company in the middle of a financial year.
Why Prorate? Companies allocate bonuses based on annual performance. If you were only employed for a portion of that year, fairness dictates that you receive a percentage of the bonus corresponding to your tenure during that period.
How the Bonus Pro Rate Calculator Works
This calculator determines your payout using a precise day-count method. While some simple estimates use months (e.g., 6/12 months), using exact days is the standard for payroll accuracy to avoid underpayment or overpayment.
The formula used is:
Step 1: Calculate Total Days in the Bonus Period (e.g., Jan 1 to Dec 31 is 365 or 366 days).
Step 2: Determine the number of "Eligible Days." This is the overlap between the Bonus Period and your Active Employment dates.
Step 3: Divide Eligible Days by Total Days to get the Proration Percentage.
Step 4: Multiply the Total Target Bonus by this percentage.
Example Calculation
Let's say an employee has a target bonus of $10,000.
Bonus Period: January 1st to December 31st (365 days).
Hire Date: July 1st (The employee joined mid-year).
Eligible Days: From July 1st to Dec 31st is 184 days.
Calculation: (184 / 365) = 0.5041 or 50.41%.
Payout: $10,000 × 50.41% = $5,041.10.
Common Scenarios for Prorated Bonuses
New Hires: Employees who start after the beginning of the fiscal year usually receive a prorated amount for their first year.
Departures: Depending on company policy, employees leaving before the payout date might forfeit the bonus, or receive a pro-rata share if the separation is due to retirement or redundancy.
Leaves of Absence: Unpaid leaves (sabbaticals, unpaid medical leave) are often deducted from the eligible days count.
Part-Time Adjustments: If an employee switches from full-time to part-time, the bonus may be prorated based on FTE (Full-Time Equivalent) status, though this calculator focuses on calendar duration.
FAQ
Does this calculator account for leap years?
Yes, the logic calculates the exact difference in days between the dates selected, so a 366-day leap year is handled automatically.
Do weekends count?
In most standard bonus contracts, proration is based on calendar days, not business days. This calculator uses calendar days (including weekends and holidays) which is the industry standard for annual accruals.