The math is ordinary math
Every result comes from a formula you could check with a pencil: the standard payment formula for a loan, the IRS brackets for income tax, the ratio of two BLS price indexes for inflation. No number is estimated by a language model or copied from another calculator. Each calculator shows its formula under “How this is calculated”.
Where the figures come from
Any figure you did not type comes from the agency that publishes it: the IRS, BLS, Census Bureau, HUD, BEA, EIA, Freddie Mac, CMS, FHFA, USDA and the state tax departments. We download each release, compare it with the one before, and keep the copy we used, so a page can tell you which month’s numbers it is on. If a release is late or fails those checks, the page keeps the last good copy and says how old it is.
What the site leaves out
City and county income taxes, like New York City’s or Philadelphia’s. Insurance pricing that depends on your driving record or credit. Anything that needs your exact street. Where one of those would change your answer, the calculator says so and lets you type your own figure instead.
Forty years of the same numbers
The data page has a table of inflation, what $100 buys, the 30-year mortgage rate, the standard deduction, the 401(k) limit and the conforming loan limit from 1980 to now, for when a number needs its history beside it.
Measurements and allowances stay apart
The cubic yards a slab needs is a measurement. The extra bags you buy in case some spill is an allowance. Tools that involve both show them on separate lines, so you can see which is which.
When an official figure changes
When BLS publishes a new month of CPI, Freddie Mac its weekly rate, or the IRS next year’s limits, the pages that use them change with the next update and the date on the page moves with them.
Common questions about what an estimate is, and what it is not, are answered in detail on the FAQ.
Every dataset the site uses, its date and where it comes from →