The 13th month pay is a mandatory monetary benefit given to employees in certain countries, typically payable before the end of the year. While regular employees who have worked a full calendar year receive a full extra month's salary, employees who have worked for less than a year (due to resignation, termination, or being hired mid-year) are entitled to a pro-rated 13th month pay.
Use the calculator below to determine the exact amount based on your monthly basic salary and the duration of your service within the calendar year.
Pro-Rated 13th Month Pay Calculator
Enter your basic salary excluding allowances or bonuses.
Enter total months worked within the calendar year (1-12).
If you had leave without pay, enter the total monetary amount deducted.
Your Pro-Rated 13th Month Pay
0.00
function calculateProRatedPay() {
// Get input elements matching IDs exactly
var salaryEl = document.getElementById("basicSalary");
var monthsEl = document.getElementById("monthsWorked");
var deductionsEl = document.getElementById("unpaidLeaves");
var resultBox = document.getElementById("resultBox");
var finalResult = document.getElementById("finalResult");
var formulaDisplay = document.getElementById("formulaExplanation");
// Parse values
var salary = parseFloat(salaryEl.value);
var months = parseFloat(monthsEl.value);
var deductions = parseFloat(deductionsEl.value) || 0; // Default to 0 if empty
// Validation
if (isNaN(salary) || salary < 0) {
alert("Please enter a valid positive Monthly Basic Salary.");
return;
}
if (isNaN(months) || months 12) {
alert("Please enter a valid number of months worked (between 0.1 and 12).");
return;
}
if (deductions < 0) {
alert("Deductions cannot be negative.");
return;
}
// Calculation Logic
// Formula: (Total Basic Salary Earned during the year) / 12
// Total Earned = (Monthly Salary * Months Worked) – Unpaid Leave Deductions
var totalEarned = (salary * months) – deductions;
// Ensure total earned isn't negative
if (totalEarned < 0) {
totalEarned = 0;
}
var proRatedPay = totalEarned / 12;
// Display Logic
resultBox.style.display = "block";
// Formatting to currency style (using generic locale)
finalResult.innerHTML = proRatedPay.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Update explanation text
formulaDisplay.innerHTML =
"Calculation:" +
"((" + salary.toLocaleString() + " × " + months + ") – " + deductions.toLocaleString() + ") ÷ 12" +
"= Total Earned (" + totalEarned.toLocaleString() + ") ÷ 12";
}
The Formula for Pro-Rated 13th Month Pay
The standard formula to calculate the 13th month pay is straightforward. It is essentially one-twelfth (1/12) of the total basic salary earned by an employee within a calendar year.
13th Month Pay = Total Basic Salary Earned during the year ÷ 12
Step-by-Step Calculation
Determine the Monthly Basic Salary: Do not include allowances, overtime pay, or commissions unless company policy specifically includes them.
Count the Months Worked: Determine the number of months the employee was employed during the specific calendar year.
Subtract Unpaid Absences: If the employee had leaves without pay, the equivalent salary amount for those days must be subtracted from the total earnings.
Divide by 12: Divide the final total earnings by 12 to get the pro-rated amount.
Example Scenarios
Example 1: New Hire
Scenario: Employee A was hired on September 1st. Their monthly basic salary is 20,000. They worked until December 31st (4 months) with no unpaid absences.
Total Basic Salary Earned: 20,000 × 4 months = 80,000
Calculation: 80,000 ÷ 12
13th Month Pay: 6,666.67
Example 2: Resigned Employee
Scenario: Employee B resigned effective March 31st. Their monthly salary was 30,000. They had unpaid absences amounting to 5,000 during that period.
Gross Salary for 3 months: 30,000 × 3 = 90,000
Less Unpaid Absences: 90,000 – 5,000 = 85,000 (Total Earned)
Calculation: 85,000 ÷ 12
Pro-rated Pay: 7,083.33
Frequently Asked Questions
Does the calculation include overtime and allowances?
Generally, no. The 13th month pay is computed based on the basic salary only. It typically excludes overtime pay, night shift differentials, holiday pay, and cost of living allowances (COLA), unless these are integrated into the basic salary by contract or company practice.
Who is entitled to pro-rated pay?
Any rank-and-file employee who has worked for at least one (1) month during the calendar year is usually entitled to 13th month pay. This applies regardless of the nature of employment (regular, probationary, casual, or fixed-term) and the method of payment (monthly, daily, or piece-rate).
When should it be paid?
In most jurisdictions mandating this benefit, the 13th month pay must be released not later than December 24th of each year. For resigned employees, it is typically released as part of their final pay (back pay).