Methodology

The principle

Wrong tax numbers are the one failure this site cannot recover from. So the rule throughout is: a figure is either read from a primary source or it is not used. Where a number cannot be verified it is left null and the calculator declines to compute rather than guessing. Where a figure is carried forward from a prior year deliberately, the calculator still computes but emits a warning naming the year it came from.

Every line of every calculation carries the rule applied and the authority for it. Open Show your work on the calculator to read the full derivation.

Federal sources

Inflation-adjusted figures for tax year 2026 come from IRS Revenue Procedure 2025-32 (Internal Revenue Bulletin 2025-45). The 2026 adjusted items are in SECTION 4 of that document — not Section 3, which is taken up by modifications to the prior year’s Revenue Procedure. The widely repeated “§ 3.03” citation for the capital gains table is the previous year’s numbering and is wrong for 2026.

How the federal figures were checked

Rev. Proc. 2025-32 prints, for each bracket, a cumulative tax base — the $X plus 24% of the excess over $Y figure. That base is fully determined by the breakpoints beneath it, so recomputing it from the data file and comparing against the printed figure is a genuine independent check: one mistyped breakpoint changes the base. All four individual tables reconcile to the cent, and that check runs as a test on every build.

Three rules that are easy to get wrong

• MAGI for the net investment income tax is measured BEFORE the standard deduction. Using taxable income instead silently zeroes the tax for some taxpayers.
• The § 121 reduced exclusion prorates the maximum exclusion amount, not the gain (Treas. Reg. 1.121-3(g)). Prorating the gain overstates tax for anyone with a modest gain and a qualifying early sale.
• Unrecaptured § 1250 gain is the lesser of depreciation taken and total gain, and 25% is a maximum, not a flat rate — a taxpayer in the 22% bracket pays 22% on it.

State sources

State data is split into two halves with different verification calendars. The rate structure — the rate ladder, how gains are treated, exclusions, surtaxes, local add-ons — is statutory and verifiable at any time. The thresholds — bracket bounds and standard deductions — are indexed annually and mostly published in November and December.

39 of 51 jurisdictions have a rate structure read from a tax code or revenue department. The remaining 12 are shown in the calculator as not yet available rather than left out, so no user can mistake an unverified state for a state with no tax.

Where a figure turned out to be wrong, it is logged with its date and its primary source on the corrections page, permanently. The rules those cases produced are set out in the editorial policy; the six failure modes below are the ones that have actually occurred here.

When the published rate is not the operative rate

A rate that is written down is not always the rate in force. Three cases found while verifying states for 2026 are recorded here, because each one would have produced a wrong answer that looked entirely plausible.

Expired and superseded text

A different failure, and a subtler one. The text below is genuinely in the statute, from the statute’s own publisher. It has simply stopped applying — because it expired, because a later act replaced it, or because the copy retrieved was an old revision. A quotation carries no date with it, and nothing about these documents announces that they are out of date.

The rule this produces: a quotation is not evidence on its own. The years a provision applies to are part of the figure, and a rate quoted without them has not been verified — it has been read.

Aggregated research output

The fourth mechanism, and the one that looks most like a source. Summaries assembled from many documents arrive with citations attached, in the register of something authoritative, and are wrong in ways that are invisible without going back to the text they point at. The citation is often real; it simply does not say what the summary claims.

One such summary, checked line by line against sources already read for this site, contradicted the primary text on nine states — among them Louisiana at 6% against a flat 3%, Kansas at 2.75% against 5.2%/5.58%, Nebraska at 6.84% against a rate the statute scopes to 2026 at 4.55%, Montana as a seven-bracket state against a 4.7/5.65% ladder with separate capital gains rates, Virginia as flat against a graduated ladder, and Missouri as having no income tax at all. Two independent summaries also both gave the Arkansas top rate as 3.7%; the Department’s own 2026 formula says 3.90%.

Nothing on this site is taken from such a summary. They are useful only as a list of documents to go and read. No figure is used without verbatim text we have read ourselves — which is also why the errors above are listed here rather than sitting in the data.

When the source declares itself incomplete

The fifth shape is not an error in the document at all. The source is accurate, current and authoritative — and says on its own face that it is only part of the calculation.

Connecticut’s DRS Form CT-1040ES carries the 2026 rate ladder in Table B, under a note that it “does not include personal tax credits, the 2% phase-out or tax recapture”. The recapture in Table D reaches $3,400 for a single filer and $6,800 filing jointly. Reading the ladder and stopping would understate a large Connecticut gain by thousands of dollars, and nothing about the figure would look wrong.

So Connecticut’s rates are verified and Connecticut is still not computed. Where a document tells you what it leaves out, that sentence is part of the source.

When a repeal document names the tax but repeals its structure

The sixth shape is the most dangerous one found so far, because reading only the title of an authentic, correctly-named legislative document produces exactly the wrong answer.

Louisiana’s legislature publishes a document titled “Repeals the individual income tax”. Taken at its word, Louisiana has no income tax and no capital gains tax, and a calculator would confidently return zero. Louisiana in fact taxes a capital gain at a flat 3%.

The statute settles it in a way no summary, news report or aggregator could. La. R.S. 47:32 has two subsections. Subsection B — the graduated bracket schedule — carries “Repealed by Acts 2024, 3rd Ex. Sess., No. 11, s4, eff. Dec. 4, 2024”. Subsection A, which imposes the tax, stands unrepealed and reads: “The tax to be assessed, levied, collected, and paid upon the taxable income of an individual shall be computed at the rate of three percent on net income.” What was repealed was the structure — the ladder of brackets — and it was replaced by a single rate in the same act.

The same act reached further than the rate. Louisiana’s statutory subtractions list at R.S. 47:293(9)(a) now contains no occurrence of “capital gain”, “net capital” or “equity interest”: the business-interest exclusion formerly at (9)(a)(xvii), and item (ix), both read “Repealed by Acts 2024, 3rd Ex. Sess., No. 11”. So the act that flattened the rate also stripped the gains exclusion, and a reader who took the title at face value would have been wrong twice over.

The rule this produced: a repeal is read at the subsection it names, never at the title. A document can be genuine, current and accurately titled and still describe something narrower than its name suggests — and the amendment history, which here ends at Act 11 of 2024, is what confirms nothing later moved it.

States where a determination decides the rate

In these states the statute defines a trigger rather than a rate, so reading the code tells you the mechanism and nothing about the answer. Each needs a third kind of source: the department’s own determination for the year.

Washington is a special case: RCW 82.87.040 imposes a 7% excise on all Washington capital gains plus an additional 2.90% on the portion above $1,000,000 — a 9.9% marginal rate. Real property is exempt outright and only long-term gains are in scope. Its standard deduction is indexed under RCW 82.87.150 and published separately from any rate table; the 2026 figure was not published when this was last checked, so the 2025 amount is used under a mandatory warning.

What is out of scope

This list is deliberately explicit. If your situation involves any of these, the number this calculator gives you is incomplete — not merely approximate.

Corrections

If you find a figure that is wrong, please tell us and cite the source. Corrections to tax figures are treated as urgent. Source data for tax year 2026 is Rev. Proc. 2025-32 (I.R.B. 2025-45).