> ## Documentation Index > Fetch the complete documentation index at: https://docs-test.symmetry.com/llms.txt > Use this file to discover all available pages before exploring further. # State Income Tax Overview > Overview of state income tax (SIT) support in the Symmetry Tax Engine, covering all 50 states, five U.S. territories, and multi-state withholding. The Symmetry Tax Engine (STE) supports state income tax (SIT) calculations for all 50 U.S. states and for five U.S. territories: American Samoa, Guam, the Commonwealth of the Northern Mariana Islands (CNMI), Puerto Rico, and the U.S. Virgin Islands (USVI). Despite not technically being "states," U.S. territory taxes still use the `SIT` tax type in their unique tax IDs. This page summarizes the SIT model. Detailed setup and example calculations for each state and territory live on their dedicated per-state pages. ## The SIT model * **State-by-state rules.** The STE tracks withholding rules individually for each state and territory, so each SIT tax (for example, `01-000-0000-SIT-000` for Alabama) is calculated according to that jurisdiction's own methods. * **States that require federal values.** Some state taxes depend on federal results computed in the same run. As of 2023, Alabama and Oregon use federal income tax (FIT) results, and Massachusetts uses Social Security and Medicare results. When calculating these, make sure the necessary federal taxes are set up to run at the same time. * **Mirror-code territories.** Guam, the Commonwealth of the Northern Mariana Islands (CNMI), and the U.S. Virgin Islands (USVI) use a mirror code system and are automatically updated to use the new federal tables whenever the federal income tax tables change in the STE. * **States without an income tax.** Nine states do not levy an income tax on earned wages (Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming). Placeholder SIT tax IDs still exist for them and may need to be set up — for example, in multi-state scenarios. * **Multi-state withholding.** When an employee lives and works in different states, the STE identifies the single resident state and loops through the nonresident work states, applying each resident state's calculation type ("All," "All with No Credit," "Difference," "Full," or "None") and any reciprocal agreements. ## Key pages FAQs and the full list of state and territory income taxes with their unique tax IDs. The nine states with no income tax, their placeholder tax IDs, and the `includeNoTaxStates` option. How the STE computes withholding across resident and work states, including calculation types and reciprocity. ## Per-state and territory pages Each state and U.S. territory has its own dedicated page with setup details and example calculations. A representative sample is shown below: The pages above are only a sample. Every state and territory the STE supports has its own page nested under this overview in the navigation. For the complete list of state and territory taxes and their unique tax IDs, see [State & Territory Tax IDs (SIT)](/ste/taxes/state/state-income-taxes-sit).