Updated October 24, 2026. Quick answer: Line 13 of the California Form 540 is where you start the income calculation, with your federal adjusted gross income from Form 1040 or 1040-SR, line 11b. Registered domestic partners follow a separate rule, and the booklet lists the adjustments that change it. The number feeds line 14 and then line 15 as the first step toward California adjusted gross income.
What this line does
The form’s own wording is “Enter federal adjusted gross income (AGI) from federal Form 1040 or 1040-SR, line 11b.” It sits on side 2 of the form in the block headed “Taxable Income”. The booklet tells you to “Refer to your completed federal income tax return to complete this section.”
Line 12 comes first on that side and asks for state wages from the W-2. The federal figure that line 13 starts from is explained on Form 1040 lines 9, 10 and 11.
Who it applies to
Every filer uses line 13, with one special rule. The booklet addresses registered domestic partners: “RDPs who file a California tax return as married/RDP filing jointly and have no RDP adjustments between federal and California, combine their individual AGIs from their federal tax returns filed with the IRS.” “Enter the combined AGI on line 13.”
The booklet introduces the adjustments this way: “RDP adjustments include but are not limited to the following:” The first six items it lists are in the table below.
| Item | What the booklet lists |
|---|---|
| Bullet 1 | “Transfer of property between spouses/RDPs” |
| Bullet 2 | “Capital loss” |
| Bullet 3 | “Transactions between spouses/RDPs” |
| Bullet 4 | “Sale of residence” |
| Bullet 5 | “Dependent care assistance” |
| Bullet 6 | “Investment interest” |
What the instructions say
| Line | What the form says |
|---|---|
| Line 12, the form | “State wages from your federal Form(s) W-2, box 16” |
| Line 12, the booklet | “Enter the total amount of your state wages from all states from each of your federal Form(s) W-2, Wage and Tax Statement.” “This amount appears on federal Form W-2, box 16.” |
| Line 13, the form | “Enter federal adjusted gross income (AGI) from federal Form 1040 or 1040-SR, line 11b.” |
| Line 13, joint RDPs | “RDPs who file a California tax return as married/RDP filing jointly and have no RDP adjustments between federal and California, combine their individual AGIs from their federal tax returns filed with the IRS.” “Enter the combined AGI on line 13.” |
| Line 13, RDP adjustments | “RDP adjustments include but are not limited to the following:” (first six items listed in the table below) |
| Line 13, other RDPs | “RDPs filing as married/RDP filing separately, former RDPs filing single, and RDPs with RDP adjustments will use the California RDP Adjustments Worksheet in FTB Pub. 737, Tax Information for Registered Domestic Partners, or complete a federal pro forma Form 1040 or 1040-SR.” |
| Line 13, transfer | “Transfer the amount from the California RDP Adjustments Worksheet, line 27, column D, or federal pro forma Form 1040 or 1040-SR, line 11b, to Form 540, line 13.” |
Where the result goes next
The line 13 amount is the starting figure for line 14. The booklet says for line 15: “Subtract the amount on line 14 from the amount on line 13.” Line 14 comes from Schedule CA (540); the adjustments for pensions are covered on Schedule CA (540) lines 4 and 5, and the state overview is on California retirement taxes and whether California taxes pensions.
Edition and line numbers
This page reads California 540 Forms and Instructions, 2025 Personal Income Tax Booklet, Franchise Tax Board, and Form 540, California Resident Income Tax Return (2025), Franchise Tax Board, for tax year 2025, the current file the Franchise Tax Board served on 2026-10-24. Check the edition printed on your own form and use that edition’s line numbers.
Common mistakes
- Entering a different federal line. The form asks for “federal Form 1040 or 1040-SR, line 11b.”
- Combining two partners’ figures when RDP adjustments exist. The combine rule applies to RDPs “and have no RDP adjustments between federal and California”
- Skipping the worksheet or pro forma return. The booklet says RDPs with adjustments “will use the California RDP Adjustments Worksheet in FTB Pub. 737”
Related: California retirement taxes, whether California taxes pensions, Schedule CA (540) lines 4 and 5, and Form 1040 lines 9, 10 and 11.
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- California 540 Forms and Instructions, 2025 Personal Income Tax Booklet, Franchise Tax Board: www.ftb.ca.gov
- Form 540, California Resident Income Tax Return (2025), Franchise Tax Board: www.ftb.ca.gov
- Related official page (not quoted): Franchise Tax Board, 2025 Personal Income Tax Booklet page: www.ftb.ca.gov
Read from the state revenue documents linked above on October 24, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer or the state revenue department is the right place to confirm anything consequential.