California SB 253 Reporting: Deadlines, Requirements & Compliance Guide

California's Climate Corporate Data Accountability Act — Senate Bill 253 — requires large companies doing business in California to disclose their greenhouse gas emissions for the first time. The first Scope 1 and 2 emissions reports are due November 10, 2026.

This guide covers exactly who must comply, what must be reported, how the filing timeline works, and what companies should be doing right now to prepare.

Latest update — what changed in 2026

Two developments have changed the picture since CARB's original implementing regulations:

• The first reporting deadline moved from August 10 to November 10, 2026. CARB pulled its regulatory package back from the Office of Administrative Law to accommodate the extension. The November date is the one to plan against; the rule package itself is still being finalised.
• Initial Scope 3 reporting would cover five categories, not fifteen. At its July 21, 2026 workshop CARB proposed limiting the first mandatory Scope 3 disclosures to the five most commonly reported categories. Details in the Scope 3 section below.

CARB also signalled that insurance companies will lose their SB 253 exemption from 2027, though they may be able to satisfy both California Department of Insurance and SB 253 obligations through a single integrated report.

What is California SB 253?

SB 253 was signed into law in October 2023. It requires companies with annual revenues exceeding one billion dollars that do business in California to publicly disclose their greenhouse gas emissions — initially Scope 1 and Scope 2, and eventually Scope 3 — on an annual basis.

The law is administered by the California Air Resources Board (CARB), which published implementing regulations and a draft reporting template in late 2025. SB 253 is formally known as the Climate Corporate Data Accountability Act.

Who must comply

A company is covered by SB 253 if it meets two criteria simultaneously:

• Annual revenues exceed $1 billion. This refers to total annual revenues of the reporting entity — not California-specific revenue.
• The company "does business in California." Under California's Revenue and Taxation Code, a company does business in California if it is organised or commercially domiciled there, or if its California sales, property, or payroll exceed the state's threshold amounts. Any company with meaningful commercial activity in California — sales offices, distribution, employees — almost certainly qualifies, regardless of where it is headquartered.

Subsidiaries and parent companies: CARB's implementing rules require reporting at the parent entity level on a consolidated basis. If your parent company exceeds $1 billion in revenue and does business in California, the parent entity is the reporting entity — not an individual subsidiary.

M&A and mid-year changes: If a company crosses the revenue threshold during the year or completes an acquisition that brings it into scope, the obligation applies from the next full reporting year. Partial-year transitions do not trigger mid-year filing obligations.

The universe of covered companies is large — potentially thousands of US and multinational companies with California operations. The threshold is total global revenue, which catches many multinationals that may not consider themselves "California companies."

What must be reported in 2026

For the first reporting cycle, due November 10, 2026, companies must report:

• Scope 1 emissions — direct GHG emissions from sources owned or controlled by the reporting entity: stationary combustion, mobile combustion, process emissions, and fugitive emissions such as refrigerants.
• Scope 2 emissions — indirect emissions from purchased electricity, steam, heat, and cooling.

Scope 3 reporting is not required for the first filing. Under the approach CARB set out at its July 21, 2026 public workshop, Scope 3 disclosure would begin with the 2027 reporting cycle — and, significantly, would initially be limited to five of the fifteen GHG Protocol Scope 3 categories rather than all fifteen.

CARB proposed the narrower starting scope in response to stakeholder evidence on compliance cost and data availability, selecting the categories that are, in its words, “already frequently reported, and already have some of the most established data sources and mature quantification methods.” The five are:

• Category 1 — Purchased goods and services
• Category 3 — Fuel- and energy-related activities
• Category 5 — Waste generated in operations
• Category 6 — Business travel
• Category 7 — Employee commuting

Reporting on the remaining ten categories would be voluntary, and CARB has not set a date for when — or whether — they become mandatory. This is a proposed framework, not a final rule: CARB is running stakeholder listening sessions through August and September 2026 before finalising the regulation, so the category list and timing can still move. Mapping your material value-chain categories now remains the sensible investment, and the five above are the rational place to start.

Reporting follows GHG Protocol methodology. Companies must apply the GHG Protocol Corporate Accounting and Reporting Standard and consolidate emissions using the operational control, financial control, or equity share approach — applied consistently across all reporting years.

CARB’s draft reporting template (published October 2025) separates mandatory core fields from voluntary disclosure fields. Mandatory fields include total Scope 1 and 2 emissions by gas type, organizational boundary approach, base year, and the material estimation methodologies used. Note that this template represents CARB’s best available guidance as of publication and may be updated before the 2026 filing deadline — companies should check CARB’s website for the current version.

How your fiscal year determines which data you report

The first filing covers your most recent completed fiscal year as of the November 10, 2026 deadline, with one important rule:

• If your fiscal year ends between January 1 and February 1, 2026 → report FY2026 data
• If your fiscal year ends between February 2 and December 31, 2026 → report FY2025 data

For most companies with a December 31 fiscal year end, the first filing covers FY2025 emissions data. Companies with non-calendar fiscal years should confirm which dataset applies before starting their data collection process. Because the deadline shifted, confirm your applicable fiscal year against CARB's final regulation before locking your data-collection scope.

Assurance requirements — what's required and when

This is one of the most misunderstood aspects of the initial SB 253 timeline.

CARB waived the limited assurance requirement for the first reporting cycle. Companies must submit their Scope 1 and 2 emissions data by November 10, 2026, but no third-party verification is required for that initial submission. This was a deliberate policy decision by CARB, recognizing that many covered companies are conducting a formal GHG inventory and public disclosure for the first time. Making assurance mandatory in year one would impose significant cost with limited benefit when underlying data and methodologies are still being established. The waiver applies specifically to the 2026 filing — it is not an indefinite exemption.

The assurance schedule going forward is shown in the table below. Limited assurance — expected from the 2027 filing cycle onward — is a less intensive standard than financial audit assurance. The assurance provider performs analytical procedures and targeted inquiries rather than a full substantive audit, issuing a negative-form statement (nothing came to our attention indicating material errors) rather than a positive opinion. Reasonable assurance, expected from 2030, is comparable in scope and rigor to a full financial audit.

For the 2027 cycle CARB proposed that limited assurance be performed under one of five accepted standards: AA1000AS v3, AICPA AT-C Section 210, ISO 14064-3:2019, ISAE 3410 and ISAE 3000, or ISSA 5000 (for engagements after December 15, 2026). Confirming early that your assurance provider works to one of these is worth doing before the 2027 engagement is scoped.

Companies that treat the 2026 filing as a genuine data quality exercise — documenting sources, establishing traceable calculation chains, and recording clear methodology decisions — will find the 2027 limited assurance engagement significantly less disruptive. Data quality issues identified and resolved now are far cheaper to fix than those flagged by an external assurance provider under deadline pressure.

Penalties and enforcement

CARB can impose civil penalties of up to $500,000 per reporting year for willful non-compliance. For the initial 2026 filing cycle, CARB has indicated it will exercise enforcement discretion for good-faith efforts — companies demonstrating active compliance are unlikely to face penalties even if their first submission contains minor gaps.

This does not mean the November 10 deadline is optional. CARB's enforcement discretion applies to quality and completeness, not to whether a report was filed. Non-filing is a materially different position from filing with acknowledged limitations.

How SB 253 differs from SB 261

These two laws are frequently conflated — they are separate statutes with different requirements and different legal statuses.

SB 261 — the Climate-Related Financial Risk Act — requires companies with revenues above $500 million to publish a climate-related financial risk report aligned with TCFD. Enforcement is currently paused: the Ninth Circuit granted an injunction pending appeal on November 18, 2025, days before the first reports were due, and heard oral argument on January 9, 2026. The stay remains in place. The injunction does not invalidate SB 261 — if it is lifted, obligations resume, so companies in scope should keep preparing rather than stand down.

SB 253 — the emissions disclosure law covered in this guide — faces no current legal injunction and remains fully in force.

What companies should be doing right now

With the November 10, 2026 deadline approaching, here is a practical six-step preparation sequence:

• Confirm scope. Check the revenue threshold and California nexus. If in doubt, you are almost certainly in scope.
• Establish your organizational boundary. Choose operational control, financial control, or equity share consolidation. Document the rationale — this choice determines which subsidiaries, joint ventures, and leased assets are included, and must be consistent across reporting years.
• Inventory Scope 1 sources. Identify all owned or controlled combustion, process, and fugitive emission sources globally: stationary combustion (natural gas, diesel), mobile combustion (fleet), process emissions, and refrigerant leakage.
• Compile Scope 2 data. Gather electricity, steam, heat, and cooling consumption data across all relevant operations. Distinguish market-based from location-based Scope 2 where applicable.
• Select and document calculation methodologies. GHG Protocol allows multiple approaches per source category. Choose the methods appropriate to your data availability and document them — CARB’s template asks you to specify the methodology for each material source.
• Build for audit readiness now. Although assurance is not required in 2026, data quality issues found during this first filing are far cheaper to resolve than after an assurance provider flags them. Build a centralized, auditable record of emission sources, activity data, conversion factors, and methodology decisions. See our guide to audit-ready sustainability data for a detailed checklist.

Building that data infrastructure is not a one-time reporting exercise — it pays dividends across every subsequent SB 253 filing, CSRD reporting if you have EU operations, CDP submissions, and science-based target commitments.

For more on how to approach emissions assurance and what auditors look for, see our guide to GHG assurance for corporate emissions reporting.