Data sources and update policy
Last updated
Every number on this site traces back to a primary source and carries the date we last verified it. This page explains the sources, the refresh schedule, and how to report an error.
Sources by dataset
| Dataset | Primary source | Refresh |
|---|---|---|
| Federal income tax brackets, standard deduction | IRS annual inflation-adjustment revenue procedure (Rev. Proc. 2025-32 for 2026) | Each autumn when the IRS publishes; retroactive law changes as enacted |
| Social Security wage base | Social Security Administration, Contribution and Benefit Base | Each October |
| 401(k) and HSA limits | IRS notices (Notice 2025-67; Rev. Proc. 2025-19) | Annually |
| State income tax rates, brackets, deductions, exemptions | Tax Foundation compilation of state statutes, cross-checked against each state revenue department; agency sources used directly where a state changed law mid-year | January, then on every enacted change we learn of; full recheck quarterly |
| State payroll deductions (SDI, PFML, WA Cares, etc.) | Each state program's published contribution rates | Annually, typically December/January |
| Local income taxes | Comptroller of Maryland withholding memo; NYS Department of Taxation and Finance; City of Philadelphia Department of Revenue | Annually plus mid-year Philadelphia change each July |
| Sales tax rates | Tax Foundation midyear compilation (state revenue departments, Sales Tax Clearinghouse) | January and July |
| Effective property tax rates | Tax Foundation analysis of Census Bureau American Community Survey (2024 data) | Annually when new ACS data is published |
| Typical home values | Zillow Home Value Index, all homes, state level (currently July 31, 2026) | Monthly |
| Mortgage rates | Freddie Mac Primary Mortgage Market Survey via FRED (currently week of September 3, 2026) | Weekly |
How dates work
Each "Data sources & last verified" block shows two dates where relevant: retrieved, the day we last confirmed the figure against the source, and effective, the date the figure took legal effect. A recent retrieval date on an older effective date means we rechecked and nothing had changed.
What we do when a state changes its law
State legislatures frequently pass retroactive tax cuts in spring sessions. When we learn of one, we update the data file from the state agency's own publication, cite it directly, and add a note on the state's pages describing the change. In 2026 this applied to Georgia (HB 463), South Carolina (H. 4216), West Virginia (SB 392), Arkansas, and Utah (SB 60).
Known limitations
- Local income taxes are modeled only for Maryland counties, New York City, Yonkers, and Philadelphia. Ohio, Pennsylvania (outside Philadelphia), Indiana, Kentucky, Michigan, Missouri, Oregon, and Alabama local taxes are noted but not calculated.
- Some state rules (income-based phase-outs of deductions, alternate lower-income tables, tax benefit recapture) are simplified; each state page lists what is left out.
- Homeowners insurance defaults are a national rule of thumb, not state data. States with high catastrophe exposure carry a caution note.
- Property tax rates are statewide averages; county rates within a state can differ by a factor of three or more.
Corrections
If you find a figure that disagrees with an official source, contact us with the page URL and a link to the official figure. Confirmed errors are fixed in the data file, covered by a new automated test where possible, and republished. We note material corrections on the affected page.