How Federal + State Income Tax Calculator Works
The Federal + State Income Tax Calculator estimates your total tax liability across all 50 states plus DC, replacing tools like TurboTax TaxCaster with a transparent, free alternative. It computes federal income tax, state income tax, FICA (Social Security and Medicare), and shows your effective and marginal tax rates.
Enter your filing status (single, married filing jointly, married filing separately, head of household, or qualifying widow/er), gross income, and state of residence. The calculator applies the current year's federal tax brackets and standard deduction automatically. You can optionally switch to itemized deductions by entering mortgage interest, state/local taxes (capped at $10,000 SALT), charitable contributions, and medical expenses above the 7.5% AGI threshold.
For state taxes, the tool applies your state's specific bracket structure, from flat-tax states like Illinois (4.95%) to highly progressive states like California (up to 13.3%). It accounts for state-specific deductions and credits including earned income credits, property tax credits, and dependent exemptions. States with no income tax (TX, FL, NV, WA, WY, SD, AK, TN, NH) show $0 state liability.
The results dashboard breaks down your tax by category: federal, state, Social Security (6.2% up to the wage base), and Medicare (1.45% plus 0.9% Additional Medicare Tax above $200K/$250K). A visual bracket breakdown shows exactly how much of your income falls in each federal bracket, demystifying the progressive tax system.
Advanced options support self-employment tax calculations, capital gains (short and long-term at preferential rates), and common above-the-line deductions like HSA contributions, student loan interest, and traditional IRA deductions.
Key Terms Explained
- Marginal Tax Rate
- The tax rate applied to your last dollar of income—the highest bracket you reach. This is NOT the rate on all your income, only on income above the bracket threshold.
- Effective Tax Rate
- Your total tax divided by total income, representing the true average percentage you pay. Always lower than your marginal rate due to progressive brackets.
- Standard Deduction
- A flat amount subtracted from gross income before applying tax brackets. Most taxpayers use this instead of itemizing individual deductions.
- SALT Cap
- The $10,000 limit on state and local tax deductions (income, sales, and property taxes combined) enacted by the 2017 Tax Cuts and Jobs Act.
- FICA
- Federal Insurance Contributions Act taxes funding Social Security (6.2%) and Medicare (1.45%). Employers match these amounts; self-employed pay both halves.
- Progressive Tax
- A system where higher income is taxed at increasingly higher rates. Only the income within each bracket is taxed at that bracket's rate, not all income.
Who Needs This Tool
Wants to verify their paycheck withholdings are on track to avoid a surprise tax bill or an excessively large refund at filing time.
Earning $95K in self-employment income and needs to calculate quarterly estimated payments including self-employment tax to avoid underpayment penalties.
Considering a move from New York to Texas and wants to quantify exactly how much state income tax they'd save on a $120K salary.
Has income from Social Security, a pension, and IRA withdrawals, and needs to understand how much is taxable and at what rates.
Earns $50K at a W-2 job plus $25K from a side business and wants to see the combined tax impact including self-employment tax on the side income.
Methodology & Formulas
Federal tax uses the current year's IRS bracket tables applied progressively. Standard deduction is $15,000 (single) / $30,000 (MFJ) for 2026. State calculations use each state's published rate tables. FICA applies 6.2% Social Security on wages up to the wage base ($168,600 for 2025, indexed) and 1.45% Medicare on all wages. Self-employment tax applies both halves (12.4% + 2.9%) with the 50% above-the-line deduction. Capital gains rates are 0%/15%/20% based on taxable income thresholds.
Pro Tips
- Compare your marginal rate to your effective rate—many people overestimate their tax burden because they confuse the two.
- If your effective rate seems high, run the calculation with itemized deductions to see if they exceed your standard deduction.
- Use the state comparison to quantify relocation savings—high earners can save $10,000-$50,000+ annually by moving from CA/NY to a no-income-tax state.
- Self-employed users: set aside 25-30% of net income for taxes (not gross). The self-employment tax alone is 15.3% before income tax.
- Max out pre-tax deductions (401k, HSA, traditional IRA) before comparing results—these can drop you into a lower bracket.