Data sources
- Federal brackets: IRS Revenue Procedure releases (Rev. Proc.) for the current tax year, plus IRS Topic No. 559 and Publication 17.
- Standard deduction & filing statuses: IRS Publication 501 and the annual inflation-adjustment Rev. Proc.
- FICA (Social Security & Medicare): SSA Annual Statistical Supplement and IRS Publication 15 (Circular E).
- Self-employment tax: IRS Schedule SE instructions and Publication 334.
- Long-term capital gains: IRS Topic No. 409 and the annual Rev. Proc. thresholds.
- State income tax rates: Tax Foundation "State Individual Income Tax Rates" report and each state department of revenue.
- Property tax rates: Tax Foundation effective-rate data and county assessor publications.
Federal income tax formula
For every income-style calculator we follow the same pipeline:
- Gross income — wages, self-employment, investment, retirement.
- Subtract pre-tax adjustments — traditional 401(k), HSA, traditional IRA (when deductible), self-employment tax deduction.
- Subtract the larger of the standard deduction or your itemized total to get taxable income.
- Apply the 2026 marginal brackets for your filing status: each slice of income is taxed at its bracket rate, not your top rate.
- Subtract nonrefundable credits dollar-for-dollar (capped at tax owed).
State income tax
State tax engines differ in complexity (some are flat, some graduated, nine have no income tax at all). To keep the experience fast, we estimate using each state's average effective income tax rate. This is accurate within a few percentage points for most filers but does not model state-specific deductions, credits, or city taxes (NYC, San Francisco, etc.). For an exact filing number, see the relevant state department of revenue or a licensed CPA.
FICA
- Social Security: 6.2% on wages up to the annual wage base ($184,500 for 2026).
- Medicare: 1.45% on all wages.
- Additional Medicare: 0.9% on wages above the filing-status threshold.
Self-employment tax
Self-employment tax is computed on 92.35% of net SE earnings: 12.4% Social Security (subject to the wage base) plus 2.9% Medicare. Half of SE tax is deductible above the line when computing federal income tax.
Long-term capital gains
We layer your long-term gain on top of your ordinary taxable income and apply the 2026 LTCG brackets (0%, 15%, 20%) for your filing status. Net Investment Income Tax (NIIT) and state-specific treatment are noted in the relevant calculator but not always added by default.
Update schedule
We refresh the calculator engines on this cadence:
- Annually, immediately after the IRS publishes inflation-adjusted brackets and limits (typically late October).
- Quarterly for state effective-rate refreshes against Tax Foundation data.
- Ad hoc, within 14 days of any federal tax-law change that affects rates, credits, or limits (e.g., new tax legislation).
Limitations
Our calculators are estimation tools, not tax preparation software. They do not compute Alternative Minimum Tax (AMT), Net Investment Income Tax, state-specific credits, local income taxes, or filings for trusts and estates. For exact filing figures, use the recommended tax software on each calculator page or consult a licensed CPA.
Verifying our numbers
Every calculator shows a "How we calculated this" breakdown beneath your results — listing the brackets applied, the deduction used, credits subtracted, and the effective and marginal rates. Cross-check that breakdown against the source documents above. Spot a discrepancy? Let us know.