Sources and methodology

No figure on Actualsum is written from memory. Each one is transcribed from a primary publication, the publication is linked from the page that uses it, and the date a person last opened it is recorded. This page lists them.

Federal withholding and payroll tax

Federal income tax withholding uses the percentage-method tables in IRS Publication 15-T, Social Security and Medicare rates from Publication 15, and the Additional Medicare Tax threshold from Form 8959. Read August 20, 2026. The calculator assumes the current Form W-4 with no extra withholding unless you enter it.

State income tax

Each of the 50 state pages carries its own source list — the state's withholding guide or rate schedule from its department of revenue — with the read date beside each link. Across all states the sources were read between August 20, 2026 and September 5, 2026. County and local income tax is modelled only where the state publishes a single table: Indiana (read August 28, 2026) and Maryland (read August 28, 2026).

Sales tax

State rates for the 18 states with a sales tax come from each state's department of revenue or comptroller — 23 source documents in all, the oldest read August 20, 2026. Where a state publishes a combined local table, the county and city rates on its page are transcribed from it:

• CDTFA — California City & County Sales & Use Tax Rates (effective 2026-07-01) — effective July 1, 2026, read August 26, 2026. For one exact address the state's own lookup is the final word.
• Texas Comptroller — City Sales and Use Tax rates (effective 2026-07-01) — effective July 1, 2026, read September 2, 2026. For one exact address the state's own lookup is the final word.
• Arizona Department of Revenue — TPT rate table (effective 2026-09-01) — effective September 1, 2026, read September 2, 2026. For one exact address the state's own lookup is the final word.

Special district taxes that apply to part of a city, and rates that changed after the effective date above, are not modelled; the page for each state says what its table does and does not include.

Other calculators

• No tax on tips — the occupation list is Occupations That Customarily and Regularly Received Tips; Definition of Qualified Tips — final rule, 91 FR 19026, Table 1 to § 1.224-1(h), effective June 12, 2026, read September 5, 2026.
• Work days — federal holidays from U.S. Office of Personnel Management — Federal Holidays (2026 and 2027 schedules, observed dates), read August 28, 2026.
• Lottery, mileage, bonus, 1099, PTO — each page lists its own IRS notice or publication with the read date in its sources block.

What “estimate” means here

The calculators reproduce the published method with the inputs you give them. They do not know your pre-tax benefits, a second job, year-to-date wages that cross a wage base, or a local tax the state does not publish in one table, so the figure is a planning number. Your pay stub and your return are the record.

Corrections

A wrong number is fixed fastest with the page URL and the published figure you expected: hello@actualsum.com.