How these numbers are produced

What "directional" means

Every figure here answers one question: roughly how large is the difference between what is withheld on a vest and what that vest adds in tax, given what you entered.

It is not a filing computation. It does not know about your credits, your dependents, your deductions beyond the standard one, other withholding, payments you have already made, a spouse's withholding, multi-state allocation, the alternative minimum tax, or anything your employer did differently from the common method.

The modeler treats all household income as salary. For a reader who itemizes, it applies the cap on state and local taxes and no other limit, and it computes California on California's standard deduction.

Below $100,000 of taxable income, a return uses the IRS Tax Table, which works in $50 steps. This site uses the rate schedule throughout, so a figure can differ from a return by a few dollars.

Use it to see the size of your shortfall before it comes due.

Where the rates come from

Federal rates and thresholds come from IRS publications and the revenue procedure for the tax year. The federal supplemental withholding rate of 22% is from Publication 15. California's 10.23% is the flat percentage the Employment Development Department publishes for bonuses and stock options; it publishes a lower one for other supplemental wages, and neither document names restricted stock units by that term. Employers commonly apply the 10.23% rate to a vest, so that is what this site models, and the pages say which category the rate comes from rather than calling it the supplemental rate. California's rate schedule comes from the Franchise Tax Board.

Each figure is recorded with its source document, that document's revision, and the date it was last read.

IRS Publication 15 (2026), sections on supplemental wages. California EDD, DE 44, Rev. 52 (4-26), page 18. Each state's own published schedules (California: Franchise Tax Board, 2026). State figures checked October 11, 2026.

What is deliberately left out

Sixteen state jurisdictions have had their treatment of a vesting share read first-hand from the governing document. Those are the states the tools compute.

Every other state is left out rather than estimated, and the tool asks for your own rate instead. That is why coverage is smaller than it could be.

What runs where

The calculators execute in your browser. The figures you type are used to compute what you see and are never sent.

• Your figures are not transmitted. There is no analytics on your entries and no server that receives them.
• Nothing is kept unless you ask. The modeler has a control that saves your entries on your own device; turning it off removes them. It is off until you turn it on.
• A saved set is refused rather than restored when its tax year or its shape no longer matches the current build, because last year's figures may not match this year's tax rules.

One live figure is fetched: the share price. The page asks this site's own price service for one stock symbol, and nothing else you enter goes with it. When that lookup fails the page shows the last price it recorded, labeled as a prior close with its date, and never presents it as current.

Why the articles and the calculator agree

Worked examples in articles on this site are not typed by a writer. They are computed at publication time by the same engine the calculator runs, and the build refuses to publish a page containing a dollar figure it cannot trace back to that engine.

A number typed by hand is out of date as soon as a bracket changes. Computing every figure keeps the articles in sync with the calculator.

Sample figures are labeled as samples wherever they appear, including inside charts, and the persona behind each one is stated on the page.

What this site does not do

These pages describe what published rates and your own entries produce. They do not recommend a course of action, and reading one does not create an advisory relationship.

That limit is on purpose. A recommendation worth acting on needs facts a public page does not have: the rest of your balance sheet, what the money is for, what you already did this year, and what your own tax professional thinks. A public page that makes a recommendation anyway is guessing at those facts.

Questions people ask

How often are the tax figures re-checked?

Federal figures are reviewed against the current IRS publications for each tax year, and the tools refuse to run a tax year they were not built for rather than quietly applying last year's schedule. State figures carry the date each was last read against its own governing document.

Why does the tool not cover my state?

Because its treatment of a vesting share has not been read first-hand from the governing document. Sixteen jurisdictions have been. The rest are left to your own entry rather than estimated, which is a deliberate limit on coverage.

Is my information stored or sent anywhere?

No. Calculations run in your browser and the figures you enter are never sent. To show a price, the page sends one stock symbol to this site's price service. The modeler can save your entries on your own device if you switch that on, and turning it off removes them.

Are the examples in articles real people?

No. Every worked example is a constructed sample, labeled as one, with the persona stated. The figures are computed by the same engine the calculator runs rather than typed by a writer.

Is this tax advice?

No. It is educational and directional. Your filing status, other income, credits, deductions, payroll settings and plan documents control your actual result, and a decision belongs with your own tax professional.