State Tax Diff: 2026 Changes We Track Publicly

Every payroll app, paystub generator and take-home calculator that touches US state taxes runs on the same fragile input: a hardcoded table of 50 states plus DC that silently rots every January, and sometimes mid-year. This page is our answer to that, applied to ourselves first. It is the complete public changelog of every change to the 2026 state tax parameters in the Kultranz take-home engine: what changed, the before and after values, what it affected, and the official source each change was verified against.

The log starts with our own corrections, because a diff log that begins empty is marketing, not a record. On October 9, 2026 we shipped three schedule corrections (Missouri, Mississippi, Ohio) after finding our engine carrying the same wrong schedules several competitor calculators were carrying at the time. Those entries are below, with citations. Everything the weekly sweep finds from here on lands here too.

The log

Newest first. Each entry is append-only: once published it is never edited, only superseded by a newer entry. The same JSON this page renders from is served verbatim, no key required, at GET https://api.kultranz.com/tax-diff/log.

  1. Missouri (MO): state income tax schedule

    October 9, 2026 · correction · verified · 2026-10-09-mo-graduated-schedule

    FieldValue
    Before{"as_modeled":"flat 2% on all taxable income","rate":0.02,"type":"flat"}
    After{"brackets":"graduated 0% to 4.7% in 1348-dollar steps (8 brackets)","standard_deduction":{"mfj":32200,"single":16100},"type":"progressive"}
    ImpactState tax was overstated for typical earners. Nine recomputed salary values in the published take-home table, the Missouri paycheck page, three Kansas City (MO) salary-page FAQs, and both state-tax-burden comparison tables, which re-ranked Missouri to #22.
    CitationsMissouri Department of Revenue (2026 withholding formula); Tax Foundation, 2026 State Individual Income Tax Rates and Brackets; verification: Engine outputs were checked against the official state schedule to the cent before publication.

    Full entry in the data corrections log

  2. Mississippi (MS): state income tax zero bracket

    October 9, 2026 · correction · verified · 2026-10-09-ms-zero-bracket

    FieldValue
    Before{"as_modeled":"4% applied from the first dollar of taxable income"}
    After{"brackets":"0% on the first 10,000 dollars (zero bracket), 4% above it","standard_deduction":{"mfj":4600,"single":2300},"type":"progressive"}
    ImpactState tax was overstated for typical earners. The Mississippi paycheck page and the Mississippi rows of the published take-home table were recomputed.
    CitationsMississippi Department of Revenue; Tax Foundation, 2026 State Individual Income Tax Rates and Brackets; verification: Engine outputs were checked against the official state schedule to the cent before publication.

    Full entry in the data corrections log

  3. Ohio (OH): state income tax floor

    October 9, 2026 · correction · verified · 2026-10-09-oh-tax-floor

    FieldValue
    Before{"as_modeled":"2.75% applied to all taxable income"}
    After{"brackets":"0% below the 26,050-dollar floor, 2.75% above it (HB 96)","type":"progressive"}
    ImpactState tax was overstated for typical earners. The Ohio paycheck page and the Ohio rows of the published take-home table were recomputed, and the state-tax-burden comparison re-ranked Ohio to #11, with Rhode Island entering the ranking at #18.
    CitationsOhio General Assembly, HB 96 (operating budget that set the 26,050-dollar floor); Tax Foundation, 2026 State Individual Income Tax Rates and Brackets; verification: Engine outputs were checked against the official state schedule to the cent before publication.

    Full entry in the data corrections log

Current data vintage

Tax year
2026
Data verified
October 9, 2026 (every schedule checked to the cent against the official source)
Engine version
1.1.0 (versions the parameters in tax_2026.json, not the code)
Scope
State income tax withholding parameters for all 50 states plus DC: tax type, flat rates, graduated brackets and state standard deductions. Federal brackets and standard deduction, FICA rates and the SSA wage base, and the 401(k) elective-deferral limit are re-verified in the same pass.
Last sweep
October 13, 2026, result: no parameter changes detected

Sources named per entry. Primary references: State departments of revenue (for example https://dor.mo.gov/ and https://www.dor.ms.gov/), Ohio General Assembly, HB 96 (https://legislature.ohio.gov/), Tax Foundation, 2026 State Individual Income Tax Rates and Brackets (https://taxfoundation.org/data/all/state/state-income-tax-rates-2026/), IRS Rev. Proc. 2025-32 (TY2026 federal figures) and SSA 2026 wage base ($184,500).

The vintage block is the honest headline: it says when every schedule was last verified to the cent and which engine version carries them. It updates with every sweep, including the ones that find nothing, because “checked and unchanged” is a claim worth timestamping.

State Tax Diff, the product

Reading this page is free and stays free forever; it is the record and the proof of work. The product is for teams who need the log to arrive at their doorstep, verified, the day it happens, instead of someone remembering to check a website.

State Tax Diff Monitor, $9/mo (launch pricing) includes:

  • Weekly verified sweep of the state income tax withholding parameters for all 50 states plus DC: tax type, flat rates, graduated brackets and state standard deductions, plus the TY2026 federal figures, FICA constants and the 401(k) deferral limit the engine consumes.
  • The JSON changelog feed: every entry with before and after values, impact and citations, identical to this page’s data, delivered via the public API endpoints (/tax-diff/log, /tax-diff/vintage) with priority API access across the calculator and diff endpoints
  • Email alerts (ships with the first paid seat; the weekly sweep already runs), the day a change is verified, not the day the sweep notices it: pending entries only alert after a human has checked the official source.
  • A named contact who answers what the entry means for your numbers.

State Tax Diff Pro, $19/mo (launch pricing) adds:

  • Everything in Monitor.
  • Webhooks: verified diff entries POSTed as JSON to your endpoint within an hour of verification, so your pipeline consumes the change without polling.
  • SLA: parameter changes published by a state are verified and logged within five business days, the log and vintage endpoints are served at 99.9% monthly availability, and support gets a one-business-day response.

What we explicitly do not cover

No tier adds these, because honest scope beats a checkbox:

  • Local jurisdictions. City and county income taxes (New York City resident tax, Philadelphia, Ohio school district taxes and the rest) are not modeled or monitored.
  • Employer-side payroll taxes. SUI wage bases and rates, state disability insurance mechanics and similar employer-borne tables are out of scope.
  • Filing, of any kind. This is a parameter feed, not a filing product: no returns, no W-2s, no e-file, no advice. The numbers here make your estimator honest; they do not make it a tax authority.

Who this is for

Four kinds of buyer told us the same thing in different words: keeping state tables current is unpaid, invisible work that only gets noticed when it breaks.

Source-available accounting with payroll. SlowBooks-Pro 2026 is a free, source-available desktop accounting app with US payroll, and its state withholding doc states the maintenance burden exactly: “Rates change every January”, states move mid-year (Utah went to 4.45% on 2026-06-01), local rules are simplified away (“Local jurisdictions are not modelled individually”), and the standing instruction is to “update tables.py and regenerate this file together”, under a bolded “Verify before filing.” That is a weekly monitoring subscription wearing a different hat: the feed replaces the January scramble and the mid-year surprise.

npm payroll-tax packages. @molecule/api-payroll-tax-us (repo molecule-dev/molecule) is the honest version of this problem on a package manager: it ships federal withholding via IRS Pub 15-T and a state registry with six built-in state calculators (CA, NY, TX, FL, IL, MA), supports tax years 2024 and 2025 only, and throws on an unsupported year rather than silently using stale tables. Its own README draws the line: “Local/city taxes, SDI/SUI, and W-4 step-level adjustments are not modeled”, with outputs described as “preview/planning figures, not filed-payroll-grade numbers”. A verified 50-state diff feed is the missing input between that package and the states it does not cover.

Paystub generators. The GitHub paystub-generator search returns dozens of actively shipped apps (for example Frostbite1536/Paystub-Generator, whose README advertises a “Real-time paystub preview” and PDF styling). What their READMEs do not advertise is a state schedule engine, because almost none has one: the operator types deductions by hand or hardcodes a flat rate, so every state change lands on the customer’s document silently wrong. A diff feed plus the free Kultranz paycheck API is the cheapest honest upgrade in that market.

2026 take-home calculator sites. Our own corrections log records that when Missouri, Mississippi and Ohio shipped their 2026 schedules, “Several other 2026 take-home calculators were carrying the same wrong schedules at the time” (data corrections log). If you run one of those calculators, this feed is how you learn about the next Missouri before your users do, with the before and after values and the citations ready to paste into your own changelog.

Start

Email [email protected] with the subject “State Tax Diff” and one line about what you build. You get the current feed, the verification workflow behind it and a launch-price invoice. The $9 tier can also be evaluated against this page for as long as you like, free, because the page is the product’s proof of work.

Frequently Asked Questions

Yes, byte for byte. The page, the API endpoint and the alert feeds are all driven by one canonical changelog file (alert delivery activates with the first paid seat). The log is free and stays free. What you pay for on top of it is the weekly verification labor, the email alerting and the feed formats - and, on the Pro tier, the webhooks and the SLA - not access to the record.

The full 50-state plus DC parameter set is swept weekly by scheduled automation. When a sweep detects a difference, the entry lands in this log marked pending, then a human verifies it against the official state publication, fills in the citations and marks it verified. Mid-year rate moves (states do them; Utah moved to 4.45% on June 1, 2026) are exactly why the cadence is weekly and not annual.

Because the three seed entries in it are our own corrections, shipped 2026-10-09 and verified to the cent against the official Missouri, Mississippi and Ohio schedules. A vendor with an empty changelog is not showing you zero changes, it is showing you zero visibility. The full record, including what we got wrong, is on the data corrections log page.

No, and no tier adds them. We monitor state-level income tax withholding parameters: type, flat rates, graduated brackets, state standard deductions, plus the federal figures and FICA constants the engine uses. Local and city jurisdictions, employer-side taxes like SUI, and anything to do with filing are explicitly out of scope.