It is the California underpayment penalty tax form. If you want to annualize your income, you can complete the form by entering your income and deductions by qtr in Part lll of the form. Use the Part lll schedule ONLY if you earned taxable income at an UNEVEN RATE during 2024.
If more of your income was earned later in the year, annualizing your income could reduce or eliminate the penalty for underpayment of estimated taxes. 5805 Instructions (html) 2024 Instructions for 5805 Form, Underpayment of Estimated Tax by Individuals and Fiduciaries