function calculateIllinoisPayroll() {
var gross = parseFloat(document.getElementById('grossPay').value);
var freq = parseFloat(document.getElementById('frequency').value);
var status = document.getElementById('filingStatus').value;
var ilExempt = parseFloat(document.getElementById('ilExemptions').value) || 0;
var preTax = parseFloat(document.getElementById('preTax').value) || 0;
var postTax = parseFloat(document.getElementById('postTax').value) || 0;
if (isNaN(gross) || gross 0) {
if (status === 'single') {
if (adjustedAnnual <= 11600) fedTaxAnnual = adjustedAnnual * 0.10;
else if (adjustedAnnual <= 47150) fedTaxAnnual = 1160 + (adjustedAnnual – 11600) * 0.12;
else if (adjustedAnnual <= 100525) fedTaxAnnual = 5426 + (adjustedAnnual – 47150) * 0.22;
else fedTaxAnnual = 17168 + (adjustedAnnual – 100525) * 0.24;
} else {
if (adjustedAnnual <= 23200) fedTaxAnnual = adjustedAnnual * 0.10;
else if (adjustedAnnual <= 94300) fedTaxAnnual = 2320 + (adjustedAnnual – 23200) * 0.12;
else if (adjustedAnnual <= 201050) fedTaxAnnual = 10852 + (adjustedAnnual – 94300) * 0.22;
else fedTaxAnnual = 34337 + (adjustedAnnual – 201050) * 0.24;
}
}
var fedTaxPerPeriod = fedTaxAnnual / freq;
// FICA
var ssTax = taxableForFed * 0.062;
var medTax = taxableForFed * 0.0145;
// Illinois State Tax (Flat 4.95%)
// 2024 Illinois Personal Exemption is $2,775
var ilExemptionValue = (ilExempt * 2775) / freq;
var ilTaxable = taxableForFed – ilExemptionValue;
if (ilTaxable < 0) ilTaxable = 0;
var ilTax = ilTaxable * 0.0495;
var totalDeductions = fedTaxPerPeriod + ssTax + medTax + ilTax + preTax + postTax;
var netPay = gross – totalDeductions + preTax; // Adding back preTax because it was already removed from gross logic
document.getElementById('resGross').innerText = '$' + gross.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resFedTax').innerText = '- $' + fedTaxPerPeriod.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resSS').innerText = '- $' + ssTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resMed').innerText = '- $' + medTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resStateTax').innerText = '- $' + ilTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resDeductions').innerText = '- $' + (preTax + postTax).toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resNet').innerText = '$' + (gross – (fedTaxPerPeriod + ssTax + medTax + ilTax + postTax + preTax)).toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resultsArea').style.display = 'block';
}
How to Calculate Illinois Payroll Taxes
Calculating payroll in Illinois is unique compared to many other states because Illinois utilizes a flat income tax rate. Unlike the federal government which uses progressive brackets, every dollar earned in Illinois (above exemptions) is taxed at the same percentage.
1. Illinois State Income Tax Rate
As of 2024, the Illinois state income tax rate is 4.95%. This rate applies to your taxable income after taking into account personal exemptions. For the 2024 tax year, the base personal exemption amount is $2,775 per person. This means if you claim yourself, the first $2,775 you earn annually is generally not subject to state tax.
2. Federal Taxes and FICA
Regardless of which state you live in, you are subject to Federal taxes:
Federal Income Tax: Based on your filing status (Single, Married, etc.) and your earnings level.
Social Security: A fixed rate of 6.2% of your gross pay (up to the annual wage base limit).
Medicare: A fixed rate of 1.45% of your gross pay.
3. Pre-Tax vs. Post-Tax Deductions
Contributions to 401(k) plans, Health Savings Accounts (HSA), or employer-sponsored health insurance premiums are typically "pre-tax." This means these amounts are subtracted from your gross pay before taxes are calculated, effectively lowering your taxable income and the amount of tax you owe.
Example Calculation
If an employee in Illinois earns $2,500 bi-weekly ($65,000 annually) and is single with one exemption:
Gross Pay: $2,500.00
Illinois State Tax (4.95%): ~$118.49 (After exemption)
Social Security (6.2%): $155.00
Medicare (1.45%): $36.25
Federal Income Tax: ~$208.00 (Estimated)
Estimated Net Pay: ~$1,982.26
Illinois Minimum Wage 2024
When processing payroll, employers must also ensure compliance with the Illinois minimum wage. As of January 1, 2024, the minimum wage in Illinois is $14.00 per hour for workers aged 18 and older. This is scheduled to increase to $15.00 per hour on January 1, 2025.