How We Calculate: Data Sources & Methodology
Every US calculator on this site is built from primary government sources, reviewed when official figures change, and labeled with the tax year and last-updated date it reflects. This page explains where the numbers come from and how we keep them accurate.
Primary data sources
We only use official, primary sources for tax and benefit figures — never third-party summaries. The 2025 figures in our calculators come from:
- Internal Revenue Service (IRS)
Federal income tax brackets, standard deductions, contribution limits (401(k), IRA, HSA), and FICA rules. Annual inflation adjustments are taken from the IRS revenue procedures published each fall.
- Social Security Administration (SSA)
Social Security wage base, benefit formulas, bend points, and cost-of-living adjustments.
- State departments of revenue
State income tax brackets, standard deductions, and state-specific payroll taxes (for example SDI and family-leave contributions) for all 50 states and DC, sourced from each state's own revenue agency.
- U.S. Bureau of Labor Statistics (BLS)
Consumer Price Index data used by the inflation calculator.
When and how figures are updated
Federal tax figures are updated when the IRS publishes its annual inflation adjustments (typically October–November for the following tax year). State figures are reviewed against each state revenue agency's published tables at the same time, and again whenever a state passes mid-year rate changes.
Each calculator shows its own "Last updated" date and the tax year its figures reflect, in the "How We Calculate" section on the page. If those two labels ever disagree with an official source, treat the official source as correct and tell us so we can fix it.
How results are verified
Every calculator's formula is documented on its page, so you can check the math yourself. When a calculator is built or its figures are updated, results are cross-checked against worked examples from official publications (for example, IRS withholding examples and state tax tables).
All calculations run in your browser. We don't store the numbers you enter, and no sign-up is required to use any calculator.
What our calculators are — and aren't
These tools produce estimates for planning and comparison. They are not tax, legal, or investment advice, and they can't capture every personal circumstance — local city taxes in some jurisdictions, unusual filing situations, or employer-specific benefit rules may change your real numbers. For decisions with real money at stake, confirm with a CPA, CFP, or the relevant agency.
Corrections
Found a figure that doesn't match an official source? Email us via the contact page with the calculator URL and the source you checked. Verified corrections are deployed with priority and the page's last-updated date is bumped.