Are these guides updated?

Yes, and the examples update themselves — they are computed from the same data as the calculators rather than typed in. Every change to that data is recorded in the tax data changelog with the date and the source.

Which guide should I read first?

If you have never worked through how the calculation happens, start with how income tax is calculated. If you have, and something about your payslip does not make sense, marginal versus effective rate is usually the one that resolves it.

Do these count as tax advice?

No. They explain how rules work; they cannot know whether one applies to your situation. Anything turning on judgement about your facts needs a licensed professional, and the guides say where that line is.

Where do the figures come from?

The IRS revenue procedure for federal figures and each state's own department of revenue for state figures, with the document and date recorded. The sources page lists every parameter used anywhere on the site.

2026 · 6 guides

Tax guides

How the US tax system actually works, explained with the arithmetic rather than around it — and grounded in figures read off the documents that set them.

Written and edited by Pablo Ruiz QuinteroSources checked September 1, 2026Reviewed 2026-09-02

The guides

How income tax is calculatedGross income, AGI, taxable income, brackets, credits — the five steps in order, worked through on a real salary.Marginal vs effective tax rateTwo rates, and only one of them is what you pay. The most widespread misconception in personal tax.The W-4, line by lineEvery step with the exact entries for five common situations. Allowances were removed in 2020; most advice describes the old form.How to file your tax returnDocuments, deadlines, the four filing routes, extensions, payment plans and amending afterwards.What changed in 2026The indexed figures that rose, the state rates that moved mid-year and were backdated, and the thresholds that have not moved since 1978.Are tax estimators accurate?The arithmetic almost never fails; the data often does. What we found auditing the category, including our own errors.

Comparisons

Compare all 51 statesThe same salary run through every state's own rules, ranked.The nine states with no income taxWhat each one takes instead, and who actually comes out ahead.

What these are, and what they are not

Each guide is built on the same verified data as the calculators, so the worked examples are computed rather than illustrative. When a guide says a salary produces a particular figure, that figure came from the engine and moves if the underlying rate changes.

That matters more than it sounds. Of 37 states checked against their own department of revenue, 12 carried a wrong rate, threshold or credit in the compiled sources — and an article with hardcoded examples goes stale silently in exactly the same way a rate table does.

What they are not is advice. They explain how a rule works; they cannot know whether it applies to you. Where a situation turns on judgement about your facts rather than arithmetic over your figures, the guides say so and point at a professional rather than at another page.

Each carries a byline, a verification date, and a section naming the documents its figures came from.

Why these six and not others

Each of these exists because it answers a question that comes up repeatedly and is answered badly almost everywhere else — usually because the answer requires arithmetic that a general article avoids.

The marginal versus effective distinction is the clearest case. It is the single most widespread misconception in personal tax, it makes people turn down work and misjudge what a retirement contribution saves, and explaining it properly needs worked numbers at several incomes rather than a definition.

The W-4 guide exists because the form changed in 2020 and most of what is written about it still describes the old one. Advice about "claiming zero" is advice about a form that no longer has the field.

And the accuracy guide exists because we audited the category and found first-page results serving the previous year's figures. That is not a comfortable thing to publish from inside the same category, which is roughly why it is worth having.

What is not here: filing walkthroughs for specific software, anything requiring judgement about your circumstances, and general personal finance advice. Those are either somebody else's job or a professional's.

Where to go next

Income tax calculatorRun any of this on your own salary.How the figures are verifiedThe method behind every number in these guides.SourcesEvery parameter with its document and date.Property tax by countyThe other half of the picture.

Questions

Are these guides updated?: Yes, and the examples update themselves — they are computed from the same data as the calculators rather than typed in. Every change to that data is recorded in the tax data changelog with the date and the source.
Which guide should I read first?: If you have never worked through how the calculation happens, start with how income tax is calculated. If you have, and something about your payslip does not make sense, marginal versus effective rate is usually the one that resolves it.
Do these count as tax advice?: No. They explain how rules work; they cannot know whether one applies to your situation. Anything turning on judgement about your facts needs a licensed professional, and the guides say where that line is.
Where do the figures come from?: The IRS revenue procedure for federal figures and each state's own department of revenue for state figures, with the document and date recorded. The sources page lists every parameter used anywhere on the site.