Before you start

An SSN or ITIN
Form W-4 with your employer for federal withholding
Form DE 4 with your employer for California withholding
Records of foreign income and foreign financial accounts

Step-by-step

1
Complete the W-4 and the California DE 4 on day one
California's withholding certificate is separate from the federal W-4 and uses its own allowances. Leaving it blank means the employer withholds at a default that is frequently wrong for your circumstances, and California's brackets are steep enough that the error compounds fast.
Via employerWho: YouFirst week of employment
2
Understand what State Disability Insurance now costs you
SDI is withheld from wages to fund disability and paid family leave. Until 2023 it stopped at a wage ceiling; from 1 January 2024 the ceiling was removed and it applies to every dollar. For a high earner that is a meaningful addition to the marginal rate and it does not appear in any 'top state rate' comparison.
Via employerWho: You
3
Determine your US tax residency
The substantial presence test counts weighted days across three years to decide whether the US taxes your worldwide income or only US-source income. Certain students and scholars are exempt from counting days for a period. Your visa category does not settle this.
OnlineWho: You
4
Do not assume a federal tax treaty helps your California return
The US has income tax treaties with around 70 countries and California does not conform to them. Income exempted from federal tax by treaty is generally still taxable by California. Someone moving from Phoenix, where the state return starts from federal adjusted gross income and the treaty flows through, loses that benefit entirely on crossing the state line.
OnlineWho: You
5
File federal and California returns by 15 April
The tax year is the calendar year. California's return is filed with the Franchise Tax Board and it diverges from the federal one in enough places — treaties, some retirement accounts, HSA treatment — that a first year with foreign income warrants professional help.
OnlineWho: YouBy 15 April annually
6
File an FBAR if foreign accounts exceed $10,000
Aggregate foreign financial account balances above $10,000 at any point in the year trigger a FinCEN filing, separate from your tax return. An ordinary current account at home is often enough to cross it.
OnlineWho: You

Documents you’ll need

Form W-2 from each employer, issued by 31 January
Form 1099s for freelance, interest and investment income
Passport and travel history for the substantial presence day count
Foreign account statements for FBAR reporting
Property tax bill from the Los Angeles County Assessor, if you buy

Things most newcomers don’t know

Long Beach's sales tax is higher than California's own legal ceiling, by act of the legislature.

The combined rate here is 10.5%, at the very top of the Californian range. California generally caps combined district taxes so a city cannot exceed 10.25%, and Long Beach's measure was specifically exempted from that cap by state legislation. Anaheim, twenty minutes down the 5, charges 7.75%. On a car or a large appliance the gap is hundreds of dollars, and shopping across a city line is a rational local habit rather than a joke.

Source: CDTFA — California city and county sales and use tax rates

State Disability Insurance lost its wage ceiling in 2024, and nobody's comparison table has caught up.

SDI used to stop at a wage cap. From 1 January 2024 it is withheld on every dollar of wages with no ceiling. For someone earning well above the old cap that is a straight addition to the effective marginal rate on top of 13.3%, and it appears in none of the 'highest state income tax' rankings people use to compare offers between states.

Source: California Employment Development Department — disability insurance

California ignores federal tax treaties, which most newcomers discover in April.

A treaty exemption that removes income from your federal return generally does not remove it from your California one — the state does not conform. Researchers, postdocs and graduate students at CSULB and the surrounding institutions are the most affected, because the treaty articles that cover them are exactly the ones California disregards. It is a genuine and recurring shock in a first Californian tax year.

Source: California Franchise Tax Board

Proposition 13 means your neighbour may pay a fraction of your property tax on an identical house.

California assesses property at its acquisition value with annual increases capped, so a house bought in 1990 and one bought last year carry wildly different bills on the same street. A buyer's tax is based on what they paid — which makes the running cost of ownership far higher for a newcomer than for the person next door, and makes any 'average property tax' figure for the city almost meaningless for you.

Source: Los Angeles County Assessor

Common mistakes to avoid

Leaving the California DE 4 blank and letting the employer apply a default withholding.
Assuming a federal tax treaty exemption also applies to your California return. It does not.
Comparing state income tax rates between offers without accounting for uncapped SDI.
Budgeting a purchase in Long Beach at another city's sales tax rate.
Estimating property tax from a neighbour's bill rather than from your own purchase price.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.