Estimate your adjusted take-home pay based on part-time hours or a partial working year.
Annual Total
Monthly Average
Weekly Average
Please enter valid positive numbers for all fields.
Pro Rata Factor (Hours):100%
Pro Rata Factor (Weeks):100%
Adjusted Gross Pay:–
Estimated Tax Deduction:–
Estimated Take Home Pay:–
function calculateProRata() {
// 1. Get DOM elements
var fullSalaryInput = document.getElementById("fullAnnualSalary");
var taxRateInput = document.getElementById("taxRate");
var standardHoursInput = document.getElementById("standardHours");
var actualHoursInput = document.getElementById("actualHours");
var weeksWorkedInput = document.getElementById("weeksWorked");
var payPeriodSelect = document.getElementById("payPeriod");
var resultsArea = document.getElementById("resultsArea");
var errorMsg = document.getElementById("errorMessage");
// 2. Parse values
var fullSalary = parseFloat(fullSalaryInput.value);
var taxRate = parseFloat(taxRateInput.value);
var stdHours = parseFloat(standardHoursInput.value);
var myHours = parseFloat(actualHoursInput.value);
var weeks = parseFloat(weeksWorkedInput.value);
var period = payPeriodSelect.value;
// 3. Validation
if (isNaN(fullSalary) || isNaN(taxRate) || isNaN(stdHours) || isNaN(myHours) || isNaN(weeks) ||
fullSalary < 0 || stdHours <= 0 || weeks standard, cap at standard? Usually pro-rata implies reduction, but overtime is possible.
// We will allow > 100% if someone enters higher hours, but mathematically pro-rata usually implies a fraction.
var hoursRatio = myHours / stdHours;
// Calculate Weeks Ratio (Part-year factor)
var weeksRatio = weeks / 52;
// Total Adjustment Factor
var totalFactor = hoursRatio * weeksRatio;
// Adjusted Gross Salary (Total for the period defined by weeks worked)
var adjustedGrossTotal = fullSalary * totalFactor;
// Calculate Tax Amount
var totalTax = adjustedGrossTotal * (taxRate / 100);
// Net Pay
var totalNet = adjustedGrossTotal – totalTax;
// 5. Adjust output based on "Result Display Frequency"
// The adjustedGrossTotal is essentially the earnings for the *entire duration* specified in 'weeksWorked'.
// If the user selects "Monthly", we need to normalize this.
// However, usually Pro Rata calculators show: "If I work these hours/weeks, what do I get?"
// If Frequency is Annual: Show the total amount earned over those specific weeks.
// If Frequency is Monthly: Show the amount earned per month *during the working period*.
// If Frequency is Weekly: Show the amount earned per week *during the working period*.
var displayGross = 0;
var displayTax = 0;
var displayNet = 0;
if (period === "annual") {
// Total earned in the "Year" (or rather, the period worked within that year)
displayGross = adjustedGrossTotal;
displayTax = totalTax;
displayNet = totalNet;
} else if (period === "monthly") {
// To get monthly average during the working period:
// Divide total earned by (Weeks Worked / 4.333) or simply calculate normalized monthly pay
// Standard approach: (Adjusted Annual / 52) * 4.333 is roughly monthly.
// Better: Adjusted Gross / (Weeks / 4.333) if we want "per month worked".
// Simpler math for display: (Adjusted Gross / Weeks) * 4.333
if (weeks > 0) {
displayGross = (adjustedGrossTotal / weeks) * 4.333333;
displayTax = (totalTax / weeks) * 4.333333;
displayNet = (totalNet / weeks) * 4.333333;
}
} else if (period === "weekly") {
if (weeks > 0) {
displayGross = adjustedGrossTotal / weeks;
displayTax = totalTax / weeks;
displayNet = totalNet / weeks;
}
}
// 6. Formatter
var currencyFormatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// 7. Update DOM
document.getElementById("hoursFactor").innerText = (hoursRatio * 100).toFixed(2) + "%";
document.getElementById("weeksFactor").innerText = (weeksRatio * 100).toFixed(2) + "%";
document.getElementById("adjustedGross").innerText = currencyFormatter.format(displayGross);
document.getElementById("taxDeduction").innerText = currencyFormatter.format(displayTax);
document.getElementById("finalNetPay").innerText = currencyFormatter.format(displayNet);
// Update Label dynamically based on selection
var labelSuffix = "";
if(period === "monthly") labelSuffix = " (Monthly Avg)";
if(period === "weekly") labelSuffix = " (Weekly Avg)";
if(period === "annual") labelSuffix = " (Total for Period)";
// Find the label in the highlight row and append suffix
// (Simple text replacement for clarity)
// Note: This is optional polish.
resultsArea.style.display = "block";
}
Understanding Pro Rata Pay Calculation
Calculating pro rata pay is essential for employees who work part-time hours or join a company midway through the financial year. The term "pro rata" simply means "in proportion." It ensures that your salary is calculated fairly based on the actual amount of work you perform relative to a full-time equivalent (FTE) role.
Unlike standard salary calculators that assume a 40-hour work week for 52 weeks a year, a pro rata take-home pay calculator adjusts the gross figure downward to match your specific situation. This helps in budgeting accurately when negotiating a part-time contract or estimating earnings for a short-term contract.
How the Calculation Works
To determine your adjusted salary, two primary factors are usually applied to the full-time annual salary:
The Hours Factor: This is the ratio of your contracted hours to the company's standard full-time hours. For example, if you work 20 hours a week and the standard is 40, your factor is 0.5 (50%).
The Time Factor: This accounts for the duration of employment within the year. If you only work for 26 weeks out of the 52-week year, your salary for that year is halved.
The mathematical formula generally looks like this:
Adjusted Pay = Full Annual Salary × (Your Hours / Standard Hours) × (Weeks Worked / 52)
Estimating Take Home Pay
Once the "Adjusted Gross Pay" is determined, taxes and deductions must be subtracted to find your actual take-home pay. Since tax systems vary significantly by region and often involve progressive tax brackets (where higher earnings are taxed at higher rates), this calculator uses an estimated "effective tax rate" to provide a quick snapshot.
To get the most accurate result, check your previous payslips to find your effective tax percentage (Total Tax / Total Gross Pay) and enter that figure into the "Estimated Tax & Deductions Rate" field above.
Common Use Cases
Maternity/Paternity Return: Parents returning to work often reduce their hours from 5 days to 3 or 4 days a week.
Mid-Year Starters: If you start a new job in October, you will only receive a portion of the quoted annual salary before the year ends.
Job Sharing: Two employees splitting one full-time role will split the full-time salary pro rata based on their respective hours.