Methodology

Where figures come from

Every rate, bracket, threshold and fee used by a calculator is taken from a primary source — the body that sets it — and never from another website that summarises it:

• Federal tax figures: IRS publications, form instructions, and the annual inflation-adjustment Revenue Procedure.
• Social Security wage base: the Social Security Administration’s annual announcement.
• State income tax: each state’s department of revenue schedules.
• Business filing fees: each state’s Secretary of State fee schedule.

Each stored figure carries the source it came from and the date it was last checked against that source. Those dates are shown on the pages that use them, so you can see how fresh a number is rather than assuming.

How figures are verified

1. The value is read from the primary source and recorded with a link to it.
2. It is checked a second time, against the source again, before the calculator that uses it is published.
3. Every calculation is covered by automated tests, including worked examples published by the IRS. If a change breaks one of those, it cannot be deployed.

How the calculators work

Calculators run entirely in your browser. Nothing you type is transmitted to this site or stored anywhere. Closing the tab discards it.

Money is calculated using fixed-point decimal arithmetic rather than ordinary floating-point numbers. Floating point cannot represent values like 0.1 exactly, and the error accumulates — which is acceptable in a graphics engine and not acceptable in a tax figure.

Where a result depends on an assumption you did not provide, the assumption is stated next to the result rather than hidden in the arithmetic.

What is deliberately out of scope

• Alternative minimum tax, and other situations well outside the common case.
• Local and city-level income taxes.
• Multi-state apportionment for people who worked in several states in one year.
• Anything requiring your actual filings or prior-year return data.

If your situation falls into one of these, treat any result here as a rough starting point and talk to a professional.

Corrections

When a published figure or formula turns out to be wrong, it is corrected, the fix is deployed, and a note is added here describing what was wrong and for how long. Errors will not be removed silently.

Found one? Tell us.

Correction log

4 November 2026 — California: first-year minimum tax, and what electing unlocks

The California guide overstated the first year of an S-Corp election by $800. The state waives the $800 minimum franchise tax for a newly formed S corporation filing its initial return, while still charging 1.5% on first-year income. The page charged both. Live from 20 October to 4 November.

The same page also omitted two things, both raised by a tax professional in public discussion of our California findings. California offers a pass-through entity elective tax at 9.3%, and only an entity taxed as a partnership or S corporation may elect it — so electing opens a door that a sole proprietor does not have, which the page had not said. And an electing corporation files its own estimated payments on Form 100-ES, on a different schedule from the owner’s personal ones. Both are now on the page, with sources.

Separately, the source for the income-based LLC fee was recorded in our data and shown in the fee section, but was missing from that page’s list of sources. It is now listed, and cites the statute — Revenue and Taxation Code §17942, with the §17941(d) definition that the finding turns on — rather than the form instructions alone.