A California tax audit is a formal review of your returns by one of three state agencies, and how California tax audits work depends on which agency sent the letter: the Franchise Tax Board (FTB) handles personal and corporate income tax, the California Department of Tax and Fee Administration (CDTFA) handles sales and use tax, and the Employment Development Department (EDD) handles payroll tax.1California Department of Tax and Fee Administration. Doing Business in California Publication 51 References and Resources Each has its own timeline, document demands, and appeal deadlines. Miss a response window and an assessment you could have fought becomes a final bill.
Which Agency Is Auditing You
The letterhead tells you most of what you need to know. An FTB notice means your income tax return is under review, usually because something on it didn’t match information the FTB received from an employer, a bank, a brokerage, or the IRS. The IRS shares audit results and return data with California through a formal state partnering program, so a federal change can surface in a California notice years later.2Internal Revenue Service. State Information Sharing
A CDTFA notice means your sales and use tax account is being reviewed. The CDTFA generally audits accounts on a three-year cycle, when a seller’s permit closes, or when it receives a tip or outside data. First contact is typically a phone call, followed by a letter or in-person visit if the auditor can’t reach you.3California Department of Tax and Fee Administration. Publication 76 Audits An EDD notice means your payroll filings and worker classifications are being examined.
How Far Back the Audit Can Reach
The FTB generally has four years from the date you filed to issue an assessment. If you filed before the original due date, the clock starts on the due date instead. If you never filed a return, or if the return was fraudulent, there is no time limit at all.4Franchise Tax Board. Your Tax Audit
A separate rule catches people who had a federal adjustment but didn’t tell California. Notify the FTB of the federal change within six months and the state has two years from your report to assess. Wait longer and the FTB gets a full four years. Never notify, and the statute of limitations never expires.4Franchise Tax Board. Your Tax Audit
CDTFA audits cover a standard three-year period. Sales and use tax records must be kept for at least four years, and ten years for reporting periods subject to an extended statute.5California Department of Tax and Fee Administration. Sales and Use Tax Regulations Article 18 For payroll records, the retention period is four years after the contributions become due or are paid, whichever is later, stretching to eight years if you believe you’re not an employer subject to the code or that your workers are in exempt employment.6Cornell Law Institute. California Code of Regulations Title 22, 1085-2 Required Work Records
What Records You’ll Need
Every number on your return needs a paper trail. The exact documents depend on which tax is at issue.
Income Tax
Under Revenue and Taxation Code Section 19504, the FTB can demand any books, papers, or data relevant to determining your correct tax, including general ledgers, bank statements, federal returns, and W-2 or 1099 forms.7California Legislative Information. California Code Revenue and Taxation Code RTC 19504 In practice, be ready to produce anything that supports a deduction, credit, or income figure: receipts, invoices, contracts, depreciation schedules, and mileage logs all fall within scope.
Sales and Use Tax
Revenue and Taxation Code Section 7054 authorizes the CDTFA to examine the books, papers, records, and equipment of any seller of tangible personal property or anyone liable for use tax.8California Legislative Information. California Revenue and Taxation Code 7054 CDTFA Regulation 1698 requires normal books of account, bills, receipts, invoices, cash register tapes, and the working papers used to prepare your returns.5California Department of Tax and Fee Administration. Sales and Use Tax Regulations Article 18 If you claimed a resale exemption, have the resale certificates ready. The auditor will compare your reported sales against bank deposits, income tax returns, and the tax you actually collected.
Payroll
Unemployment Insurance Code Section 1085 requires every employer to keep accurate records of all workers, their employment status, and wages paid.9California Legislative Information. California Code Unemployment Insurance Code UIC 1085 Expect the auditor to focus on how workers were classified and whether wages were reported correctly.
What the Audit Itself Looks Like
FTB Income Tax
An FTB audit usually opens with a letter explaining the scope and listing the documents the auditor wants to see. Simple audits run entirely by mail. More complex cases become office or field audits with in-person meetings. You can submit documents through the FTB’s Secure Web Internet File Transfer (SWIFT) system, which encrypts the upload and timestamps each submission.10Franchise Tax Board. Secure Web Internet File Transfer SWIFT
The auditor cross-references your records against information from employers, financial institutions, and federal records. This phase can take several months, longer for business returns with high transaction volumes. Follow-up requests arrive through the same portal or by mail. Clear, organized responses speed things up; auditors who have to chase missing documents tend to dig deeper, not shallower.
CDTFA Sales and Use Tax
After initial contact, the auditor schedules a date to begin reviewing records. You typically get two to three weeks to prepare, with extensions available if you ask.3California Department of Tax and Fee Administration. Publication 76 Audits A preliminary examination comes first, then testing. The auditor may compare total sales on your books against reported sales, check collected tax against reported tax, and verify claimed resale transactions against actual resale customers.
If early tests reveal possible errors, the auditor can shift to a detailed examination, either reviewing every transaction or sampling a representative period and projecting the results across the full audit window. When fieldwork wraps up, the auditor holds an exit conference to walk you through the findings. Records can be submitted through the CDTFA’s online services portal throughout the process.11California Department of Tax and Fee Administration. Online Services
The Federal Change Trap
Revenue and Taxation Code Section 18622 creates a reporting obligation that catches many taxpayers off guard. If the IRS changes any item on your federal return (income, deductions, credits, or penalties), you must report that change to the FTB within six months of the final federal determination.12California Legislative Information. California Revenue and Taxation Code 18622 The same six-month window applies if you file an amended federal return that increases your California tax. For individuals, the duty kicks in only when the change raises what you owe California.
Skip the notification and California’s statute of limitations never expires on that year. The FTB will eventually learn about the federal change through its information-sharing agreement with the IRS. The only question is whether you reported it first.
If You’re Being Audited on Residency
Residency audits are common for high-income taxpayers who claim to have moved out of state, and the FTB looks at far more than a mailing address. According to FTB Publication 1031, the state weighs how much time you spend in California versus elsewhere, where your spouse and children live, the state that issued your driver’s license, where your vehicles are registered, your voter registration, and the location of your bank accounts, doctors, attorneys, social clubs, and professional licenses.13Franchise Tax Board. Guidelines for Determining Resident Status Publication 1031
Two numbers matter most. Spend more than nine months in California during a tax year and you are presumed to be a resident. A safe harbor runs the other way: if you are domiciled in California but leave under an employment contract for an uninterrupted period of at least 546 consecutive days, you are treated as a nonresident, provided your return visits don’t exceed 45 days in any tax year covered by the contract and your intangible income stays at or below $200,000.13Franchise Tax Board. Guidelines for Determining Resident Status Publication 1031
Changing domicile takes more than a change-of-address form. You must abandon your prior California domicile, physically move to the new location, and show through your actions an intent to remain there permanently or indefinitely. Simply registering to vote in another state is not enough on its own.
What Happens When the Audit Ends
An audit closes one of three ways: no change, a refund, or an assessment for additional tax. When the FTB determines you owe more, it mails a Notice of Proposed Assessment (NPA) listing the additional tax, penalties, and interest.14Franchise Tax Board. Notice of Proposed Assessment The CDTFA equivalent is a Notice of Determination, which follows a Report of Field Audit summarizing the findings.3California Department of Tax and Fee Administration. Publication 76 Audits
California’s accuracy-related penalty for income tax is set by Revenue and Taxation Code Section 19164, which follows the framework of Internal Revenue Code Section 6662. The standard rate is 20 percent of the underpayment attributable to negligence, a substantial understatement of income, or other accuracy failures.15California Legislative Information. California Code Revenue and Taxation Code RTC 19164 Interest runs on top. For the period from July 1, 2025, through June 30, 2026, the rate is 7 percent per year on both underpayments and overpayments.16Franchise Tax Board. Interest and Estimate Penalty Rates Interest accrues from the original due date, so a three-year-old underpayment has already built up a meaningful balance by the time the notice arrives.
How to Protest or Appeal
The deadlines are short, and missing them locks in an assessment you might have beaten.
FTB Protest: 60 Days
You have 60 days from the mail date of the NPA to file a written protest. The protest must be postmarked or electronically transmitted by midnight on the 60th day.17Franchise Tax Board. Manual of Audit Procedures Chapter 15 Protest Explain which items you disagree with and why, and attach supporting documentation. The FTB reviews the protest and issues a Notice of Action with its decision.
CDTFA Petition for Redetermination: 30 Days
For sales and use tax, the window is 30 days from the mail date of the Notice of Determination. File a petition for redetermination within that period or pay the billed amount; otherwise, the assessment becomes final.18California Department of Tax and Fee Administration. Rule 35007 Petition for Redetermination
Office of Tax Appeals: 30 Days
If the FTB denies your protest or the CDTFA’s Appeals Bureau upholds the determination, you have 30 days from the date of the agency’s decision to appeal to the California Office of Tax Appeals (OTA). The appeal must include your name, identification numbers, the disputed amount, a copy of the agency decision, and a written explanation of your position with supporting legal authority.19Office of Tax Appeals. OTA Appeals Procedures Once OTA accepts the appeal, the agency has 60 days to file an opening brief, and you then have 30 days to reply. Hearings are conducted by a panel of administrative law judges, and their written opinions are published.
Getting Penalties Waived
Penalties are not always final. The FTB may waive them if you can show reasonable cause, meaning you exercised ordinary care and prudence but still couldn’t comply. Valid reasons include natural disasters, serious illness, the death of a family member, or reliance on competent professional tax advice that turned out to be wrong.20Franchise Tax Board. Help With Penalties and Fees
Individuals and fiduciaries request relief on FTB Form 2917; business entities use FTB Form 2924. The request must explain what happened, when it happened, and what you did to try to comply anyway. Simply not knowing about a deadline, or relying on a tax preparer without checking the return, generally does not qualify. The FTB weighs each case against your compliance history, the complexity of the issue, and whether you made a genuine effort to get it right.