According to the [Internal Revenue Code (IRC) Section 63(a)](https://www.law.cornell.edu/uscode/text/26/63), most states require individuals to file a state income tax return if they have income above a certain threshold, which varies by state. For example, in California, the [state income tax filing requirement for 2025](https://www.irs.gov/pub/irs-drop/rp-24-40.pdf) is $24,000 for married couples filing jointly and $18,500 for single individuals (Page 25). Additionally, businesses operating in a state may need to file a state income tax return, even if they don’t have a physical presence there, based on economic nexus rules.
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