California state income tax
Last updated: 2026-04-27
TL;DR / ELI5
Primary form: Form 540
BasilTax engine: Yes — we calculate this state for you
Structure: bracket
Includes Mental Health Services surtax on high earners.
California income tax at a glance
This guide explains how California fits into your overall filing picture. Your federal Form 1040 is only half the story—states add their own definitions, subtractions, credits, and withholding rules.
Most California residents will prepare Form 540 alongside the federal return. Includes Mental Health Services surtax on high earners.
Withholding and W-2 boxes
If you work in California (or your employer withholds for California), compare boxes 15–17 on your Form W-2 to what you expect on the state return. Mismatches here are a common source of balance due surprises.
Credits, deductions, and quirks
State returns often start from federal adjusted gross income (AGI) and then apply state-specific subtractions, additions, credits, and alternative minimum taxes. Read your state instructions for the exact list—this page is a hub, not a substitute for official guidance.
Verification workflow
Upload your PDFs, assign them to a return, and run compute. When BasilTax supports California end-to-end, you can trace state lines to the same documents you used for federal. When support is still in progress, use BasilTax to lock down federal and broker schedules first, then complete California manually with confidence.
Ready to tie every line to your documents?
Upload your W-2s and 1099s—BasilTax extracts fields, computes federal and state, and explains each number with citations.
Frequently asked questions
- Does California have a state income tax?
- Yes—California has a state income tax system described on Form 540. Includes Mental Health Services surtax on high earners.
- What form do I file for California?
- Most residents use Form 540 for the state return, subject to exceptions for part-year residents and special situations. Always confirm the latest state instructions each filing season.
- Does BasilTax calculate California state tax?
- Yes—BasilTax includes California rules in the computation engine so your state return can align with your federal return when you upload your documents.