How do federal income tax brackets work?

The U.S. uses a progressive tax system, meaning income is taxed in segments (brackets) at different rates. Your first dollars of income are taxed at the lowest rate, and only the portion of income within each higher bracket is taxed at that higher rate. For example, if you're in the 22% bracket, only the income above the 22% threshold is taxed at 22% — not your entire income. This is why knowing your marginal rate differs from your effective rate.

Should I take the standard deduction or itemize?

In 2026, the standard deduction is approximately $15,000 for single filers and $30,000 for married filing jointly. You should itemize if your deductible expenses (mortgage interest, state/local taxes, charitable donations, medical expenses exceeding 7.5% of AGI) exceed the standard deduction. Itemizing makes more sense for homeowners with large mortgages, high state/local tax payments, or significant charitable giving.

What is the difference between marginal and effective tax rates?

Your marginal rate is the tax rate applied to your last dollar of income — the highest bracket you fall into. Your effective tax rate is your total tax divided by your total income, giving you the actual percentage you paid overall. For most people, the effective rate is 5–10 percentage points lower than their marginal rate because income is spread across multiple brackets.

Do I need to pay estimated taxes?

If you have income not subject to withholding (freelance, self-employment, investments, rental income), you generally owe estimated taxes quarterly to avoid penalties. The safe harbor rule is to owe at least 100% of last year's tax liability (110% if your AGI was over $150,000) to avoid underpayment penalties. Use our self-employment tax calculator to estimate your quarterly payments.

What are tax credits and how do they differ from deductions?

Tax deductions reduce your taxable income (saving you $1 for every dollar in your marginal tax bracket). A $1,000 deduction saves $220 for someone in the 22% bracket. Tax credits reduce your actual tax bill dollar-for-dollar — a $1,000 credit saves you $1,000 in taxes owed. Credits are more valuable than deductions of the same amount.

Free Illinois Income Tax Calculator 2026

Free Illinois (IL) income tax calculator with 2026-specific rates. Calculate your exact income tax using real Illinois data.

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Frequently Asked Questions

What is the Illinois state income tax rate?

Illinois has a top marginal income tax rate of 4.95%. The state uses a flat tax rate on all taxable income.

Does Illinois have a flat or progressive income tax?

Illinois uses a flat income tax rate of 4.95% on all taxable income.

How do I file my Illinois state income tax return?

Illinois residents must file a state income tax return with the Illinois Department of Revenue (or equivalent agency). Most taxpayers can file electronically. The deadline typically aligns with the federal tax deadline of April 15.

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