Methodology

Every result on this site is built from four layers, computed in a fixed order so nothing gets double-counted:

1. Earn-side. The price of a purchase is after-tax money. To spend it, you first had to earn MORE than that, pay federal income tax, Social Security and Medicare (FICA), and state income tax on it, and only then have the amount left over to spend. We compute exactly how much gross income is required — not with a shortcut like price / (1 − tax rate), which is wrong whenever the purchase crosses a tax bracket boundary, but by directly solving for the gross income that nets the right amount after every applicable tax.
2. Spend-side. Sales tax, excise tax (built into the sticker price for things like gas and alcohol), tips, and mandatory fees — added on top of the item's price, using the actual combined rate for the state and, where we have county-level data, the county.
3. Ownership. For categories like a car or a home, the cost doesn't end at purchase — insurance, maintenance, financing interest, and depreciation (or appreciation) over a holding period are included too.
4. Opportunity cost. What the money could have become if invested instead, at a long-run market return, shown as a separate framing — never added into the headline cost, since "cost of capital" and "money spent" are two different questions.

We gross up the total combined cost exactly once, not each component separately — because tax brackets are non-linear, grossing up two amounts separately and adding them does not equal grossing up their sum.

Confidence, honestly stated

We do not manufacture a precision-looking number like "±7.3%" — we have no real variance data for most inputs, and a computed-looking confidence interval would itself be a fabricated number. Instead: the headline income figure uses only statutory tax rules and the numbers you typed in, so it's stated as a plain point figure. Anything that includes a population average (insurance, maintenance) or a forecast (investment return, depreciation, appreciation) is clearly labeled as an estimate and, where a genuine range exists in the underlying source, is shown as a range rather than a single number.

Every number is sourced

No tax rate, fee, or figure on this site is invented or pulled from general knowledge. Every one traces to a cited source with an as-of date — see Sources. Where we genuinely don't know something (a rate that varies too much to state one figure for, or data we haven't verified yet), we say so rather than guess — seeLimitations.

Which version of the rules you are looking at

The tax rules behind every figure on this site carry a version:2026.10.01. It is not a release number — it is the date the most recently re-checked tax rule was verified against its source. It moves when a rate is re-verified and stays put through any number of rebuilds, so it says something true about the figures rather than about the deploy.

Individual rules are older or newer than that date, and each one shows its own as-of date where it is used. If you are comparing a number you saw here against one you saw elsewhere, this is the version to quote.