California generally starts with income reported for federal purposes and then uses Schedule CA (540) to make additions and subtractions required under California law. Those adjustments can cause your California adjusted gross income (AGI) to differ from the federal AGI reported on Form 1040.
Both figures can affect your tax return, which is why understanding where they come from and how they differ is important.
Start by Adding Up Your Income
Federal AGI starts with your taxable sources of income before subtracting certain adjustments to income. Pulling figures from year-end tax documents and financial records rather than relying on memory can help prevent missing income.
Common sources may include:
- Wages, salaries, tips, and bonuses
- Self-employment income
- Taxable interest and dividends
- Capital gains
- Rental income
- Taxable pension and retirement distributions
- Taxable alimony from certain divorce or separation agreements
Not every source of income receives the same treatment under federal and California law.
For example, California does not tax Social Security benefits, even when a portion is taxable federally. When federally taxable Social Security benefits are included on the federal return, Schedule CA (540) generally provides a California subtraction for that amount.
Identifying these federal and California differences is an important part of calculating California AGI correctly.
Subtract Your Above-the-Line Adjustments
After determining federal taxable income sources, certain qualifying adjustments are subtracted before arriving at federal AGI.
Depending on your circumstances, federal adjustments to income may include:
- Deductible individual retirement account contributions
- Student loan interest
- The deductible portion of self-employment tax
- Qualifying Health Savings Account (HSA) contributions
Eligibility requirements and limitations apply to each adjustment. For example, the amount of an IRA contribution that is deductible can depend on income, filing status, and participation in an employer-sponsored retirement plan.
After these adjustments are taken into account, federal AGI is calculated. That federal calculation becomes the starting point for determining which California additions or subtractions are required.
Which Federal Tax Rules Does California Treat Differently?
California generally uses federal tax law as a starting point, but it does not conform to every federal provision. Schedule CA (540) is used to reconcile many of these differences through additions and subtractions.
Common differences can include:
- Health Savings Accounts: California does not conform to federal HSA rules, so contributions, distributions, investment activity, and other HSA transactions can require California adjustments.
- Business depreciation: California does not conform to certain federal depreciation and expensing provisions, which can result in different depreciation deductions for federal and California purposes.
- Moving expenses: California may allow qualifying moving-expense deductions in situations where federal law does not, potentially creating another Schedule CA adjustment.
- Social Security benefits: California excludes Social Security benefits from taxable income even when a portion is taxable on the federal return.
Schedule CA contains both additions and subtractions. As a result, your California AGI may be either higher or lower than your federal AGI depending on your particular income, deductions, and other tax circumstances.
These differences can also affect California deductions, credits, and other tax calculations.
What Did the 2025 Federal Tax Law Change?
The 2025 federal tax law introduced several new deductions, including deductions related to qualified tips, qualified overtime compensation, qualified passenger vehicle loan interest, and eligible taxpayers age 65 and older.
These deductions are calculated on the new federal Schedule 1-A and reported below the AGI line on Form 1040. As a result, they generally reduce federal taxable income without reducing federal adjusted gross income.
That distinction matters because many deductions, credits, and other tax benefits use AGI or a modified version of AGI when determining eligibility.
Federal and California tax treatment can also differ as tax laws change, making it important to review current California conformity rules rather than assuming that a new federal deduction receives identical treatment on the state return.
Where Modified Adjusted Gross Income Fits
Modified adjusted gross income, commonly called MAGI, starts with AGI and then modifies that figure according to the particular tax provision being calculated.
There is no single MAGI calculation that applies everywhere.
Different versions of MAGI may be used when determining eligibility or limitations for items such as:
- Roth IRA contributions
- Certain education tax benefits
- Health insurance premium tax credits
- Other income-based deductions and tax provisions
An amount added back for one MAGI calculation may not be added back for another. That is why it is important to calculate MAGI based on the specific deduction, credit, or tax rule being evaluated rather than assuming one number applies across the entire return.
Have Your Federal and California AGI Reconciled
Federal AGI is an important starting point, but it does not always tell the full story for California taxpayers. Differences involving Social Security benefits, HSAs, depreciation, moving expenses, and other provisions can cause California income to differ from what appears on the federal return.
Robert Hall & Associates has prepared California tax returns since 1971. Our tax professionals help clients identify differences between federal and California tax treatment, reconcile Schedule CA adjustments, and understand how AGI and MAGI may affect deductions, credits, and other tax benefits.
Bring your prior-year return to a complimentary discovery call or contact Robert Hall & Associates to discuss your tax situation.
