The first SB 253 filing deadline arrives in 2026, covering Scope 1 and Scope 2 emissions for fiscal year 2025. Companies that have not started their GHG inventory for the current fiscal year are already behind. The data collection window for 2025 is open now, and building the infrastructure to capture that data accurately takes longer than most teams expect.
This is not a 2025 problem that can be deferred to Q4. It is a 2025 problem that requires action in Q1 and Q2.
Table of contents
- The SB 253 timeline, in full
- Common mistakes companies make when they start too late
- A 5-step action plan
- How Dcycle accelerates readiness
The SB 253 timeline, in full
Understanding the phasing of SB 253 obligations is the starting point for any realistic compliance plan.
Fiscal year 2025 data, filed in 2026: Companies must publicly disclose Scope 1 and Scope 2 emissions. This means the data collection period for the first filing is already underway. Scope 2 reporting must cover both market-based and location-based calculations.
Fiscal year 2026 data, filed in 2027: Scope 3 emissions disclosure begins. All 15 GHG Protocol Scope 3 categories must be inventoried. Companies have until 2027 to file, but the supplier engagement and data collection process for FY2026 begins the moment the calendar turns to January 2026.
Assurance requirements (phased): The California Air Resources Board (CARB) will establish specific assurance timelines through rulemaking. Limited assurance is expected to apply first, with reasonable assurance introduced later. Companies should plan for limited assurance to apply to the earliest filing cycles.
Penalty exposure begins with the first reporting cycle. CARB can impose civil penalties of up to $500,000 per year for failure to report and up to $500,000 per year for reporting inaccurate data.
The practical implication is that companies have essentially two time-sensitive tracks: build Scope 1 and 2 infrastructure now for the 2026 filing, while simultaneously beginning Scope 3 groundwork so FY2026 data collection is systematic rather than rushed.
Common mistakes companies make when they start too late
European companies navigating CSRD faced structurally identical deadlines starting in 2024. Their collective experience reveals a consistent set of failures when preparation begins too late.
Discovering data gaps in the last quarter. Companies that began their GHG inventory in Q3 or Q4 of their reporting year found that major data sources, utility bills, logistics providers, manufacturing inputs, were unavailable, incomplete, or inconsistent. Utility data in particular often arrives weeks after the billing period ends, and consolidating it across facilities requires a data request process that cannot be compressed into a few weeks.
Using incompatible methodologies across entities. Large companies with multiple subsidiaries or facilities often found that different parts of the business had calculated emissions using different emission factors, different system boundaries, or different Scope 2 accounting approaches. Reconciling these inconsistencies before a filing deadline, rather than before the data collection process, is time-consuming and error-prone.
Underestimating the documentation requirement for assurance. Companies that had the right numbers but could not produce the methodology documentation and source data evidence required by assurance providers faced delays, qualifications, or significant additional remediation costs. Assurance providers are not interested in the output alone. They want to see the entire evidence chain.
Treating Scope 3 as a year-2 problem. Under CSRD, companies that did not begin supplier engagement until the year when Scope 3 disclosure became mandatory faced extremely low response rates and poor data quality. Supplier engagement is a multi-cycle process. Companies that began outreach 12 to 18 months before their first Scope 3 filing had significantly better coverage.
Changing consultants or tools mid-cycle. Companies that switched ESG consultants or carbon accounting platforms partway through the first reporting cycle found themselves rebuilding their inventory from scratch. Data locked in one system could not easily migrate to another. The cost of switching tools after data collection begins is much higher than the cost of evaluating tools thoroughly before starting.
A 5-step action plan
Based on what worked in European CSRD implementations, here is a structured action plan for SB 253 readiness.
Step 1: Confirm your organizational boundary.
Define which entities are included in the GHG inventory. For most companies, this follows the financial consolidation boundary, but there are choices: operational control, financial control, or equity share approaches. Document the chosen approach, identify which subsidiaries and joint ventures are in or out, and flag any entities where the determination is ambiguous. This decision locks in the scope of all subsequent data collection.
Step 2: Map your Scope 1 and Scope 2 data sources.
For each facility or entity in scope, identify the data sources that will feed Scope 1 and Scope 2 calculations: natural gas bills, fuel purchase records, refrigerant top-up logs, electricity invoices, renewable energy certificates, supplier-specific emission factors for electricity. Assign a data owner for each source and set a collection cadence. Monthly data collection is preferable to annual; it catches gaps earlier and distributes the workload.
Step 3: Stand up your data collection infrastructure.
A spreadsheet process does not scale to multi-entity, multi-facility GHG accounting with assurance requirements. Evaluate and implement a platform that supports centralized data entry across entities, method documentation at the data-point level, and Scope 2 dual methodology (market-based and location-based). The platform decision should be made and implemented before mid-year, so the second half of FY2025 data flows into the right system from the start.
Step 4: Begin supplier engagement for Scope 3.
Even though the first Scope 3 filing is not due until 2027, FY2026 data collection starts in January 2026. Effective supplier engagement requires supplier communication about what data you will need, why, and in what format. Send initial outreach to your highest-spend, highest-materiality suppliers now. Set the expectation that you will request emissions data for their supplies to your organization starting in 2026. The companies that do this step a year early have vastly better primary data quality than those that start when the deadline is imminent.
Step 5: Scope your assurance provider engagement.
Begin conversations with potential assurance providers before you need them. Many firms that provide GHG assurance have significant lead times for new client onboarding. Understanding their evidence requirements, documentation standards, and process timelines now allows you to structure your data collection accordingly, rather than retrofitting documentation after the inventory is complete.
How Dcycle accelerates readiness
Dcycle condenses what would otherwise be a six to nine month implementation project into a significantly shorter timeline, because the infrastructure is already built.
Organizational boundary setup in Dcycle takes hours, not weeks. The platform supports operational control, financial control, and equity share approaches. Subsidiaries and facilities are configured in a hierarchical structure that mirrors the company’s legal and operational organization.
Scope 1 and Scope 2 data collection is automated where possible, with direct data integrations for utility providers and standardized templates for manual entry. Market-based and location-based Scope 2 methods are supported natively, with emission factor libraries updated regularly.
Scope 3 supplier workflows are built into the platform. Suppliers receive structured data requests with clear instructions, and Dcycle tracks response rates, validates the data received, and flags categories where coverage is below the materiality threshold.
Audit trail by default. Every data point carries its evidence chain from the moment it enters the system. When the assurance provider requests methodology documentation for Category 1 purchased goods, it is already there.
For companies inside CSRD scope that are also subject to SB 253, Dcycle’s multi-framework output eliminates the need for parallel processes. The same data collection feeds both reporting obligations simultaneously.
To review how Dcycle structures a SB 253 readiness assessment and what a typical implementation timeline looks like, request a demo.
For the full regulatory overview, read SB 253: who must comply, what to disclose, and by when. For the Scope 3-specific challenge, read Scope 3 under SB 253: the hardest part of California’s climate law.