365 Days (Standard Year)
366 Days (Leap Year)
260 Days (Working Days Only)
Calculated Days: 0
Percentage of Year: 0%
Pro Rata Amount: 0.00
What is a "Per Annum Pro Rata" Calculation?
The term "pro rata" is a Latin phrase meaning "in proportion." When applied to a "per annum" (yearly) figure, it refers to calculating the specific portion of that yearly total that corresponds to a shorter timeframe. This is a critical calculation in human resources, real estate, and financial accounting.
The Pro Rata Formula
The standard formula for calculating a pro-rated annual amount based on days is:
Pro Rata Amount = (Annual Total / Days in Year) × Days in Period
Common Use Cases
New Hire Salaries: If an employee starts mid-year, their first year's pay is pro-rated from their start date to December 31st.
Service Terminations: Calculating final pay or unused benefit payouts.
Lease Agreements: Determining rent for a tenant who moves in on the 15th of the month.
Insurance Premiums: Refunding the "unearned" portion of a premium if a policy is canceled early.
Example Calculation
Imagine an employee with an annual salary of 60,000 who starts work on September 1st and works until the end of a standard 365-day year (December 31st).
Total Days: From Sept 1 to Dec 31 is 122 days.
Daily Rate: 60,000 / 365 = 164.3835 per day.
Pro Rata Total: 164.3835 × 122 = 20,034.79
Important Considerations
When performing these calculations, always verify if you should use a 365-day year or a 360-day year (often used in banking). Additionally, for payroll purposes, some organizations calculate pro rata based on "working days" (usually 260 days per year) rather than total calendar days. Our calculator allows you to select these variations to ensure accuracy for your specific contract or agreement.
function calculateProRata() {
var annualAmount = document.getElementById('annualAmount').value;
var startDateInput = document.getElementById('startDate').value;
var endDateInput = document.getElementById('endDate').value;
var daysInYear = document.getElementById('daysInYear').value;
if (!annualAmount || !startDateInput || !endDateInput) {
alert("Please fill in all fields (Amount, Start Date, and End Date).");
return;
}
var start = new Date(startDateInput);
var end = new Date(endDateInput);
// Calculate difference in milliseconds
var diffTime = end – start;
// Check if end date is before start date
if (diffTime < 0) {
alert("End date must be after start date.");
return;
}
// Convert to days (include the start day in calculation usually +1)
var diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24)) + 1;
var dailyRate = parseFloat(annualAmount) / parseFloat(daysInYear);
var proRataResult = dailyRate * diffDays;
var percentage = (diffDays / parseFloat(daysInYear)) * 100;
// Update Display
document.getElementById('daysSpan').innerHTML = diffDays;
document.getElementById('percentSpan').innerHTML = percentage.toFixed(2);
document.getElementById('amountSpan').innerHTML = proRataResult.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('proRataResult').style.display = 'block';
}