No-tax states
Some states do not levy a wage income tax. Those states often look attractive in salary-after-tax comparisons because federal tax and FICA are still there, but the state layer is minimal or zero. That does not automatically make them cheaper places to live, but it can lift the paycheck number.
Flat-tax states
Flat-tax states are simpler. The state burden tends to scale more evenly with income because the same rate applies to taxable wages. These states are usually easier to model in a lightweight calculator.
Progressive-tax states
Progressive states can look very different from flat or no-tax states as income rises. At lower salaries the difference may be moderate, but at higher salaries the effective state burden can widen the gap. That is why a 100k comparison across states is often more dramatic than a 40k comparison.
Local income taxes
Some places add city or local wage taxes on top of state rules. That can make a basic state-only estimate look too optimistic. If you work in a city with local tax, a calculator with a manual local-tax field gives you more control.
Why this matters for SEO-style salary pages
A salary-after-tax page is only useful if it reflects the user’s actual comparison intent. If the page says California, Texas, or New York, it needs a state-specific assumption layer. Otherwise it becomes thin content with the right keywords and the wrong answer.