Year-end tax planning for a California business generally develops over several months rather than beginning with a single December deadline. For business owners in Los Angeles and throughout California, the period from August through December can provide increasingly complete information about revenue, expenses, estimated-tax payments, asset activity, owner transactions, and California adjustments that may affect the year's final tax position.
This 2026 year-end tax planning timeline explains the role each month can play in that process — focusing on when different planning questions become relevant and how those topics connect before year-end. It is a general educational framework; specific tax consequences depend on the taxpayer's facts, accounting method, entity structure, and applicable federal and California rules.
Establishing a year-to-date financial baseline; using September as an estimated-tax checkpoint; incorporating finalized extended-return information in October; moving to full-year federal and California projections in November; identifying calendar-year documentation before December 31; and separating year-end activity from work that continues into filing season.
When Should Year-End Tax Planning Begin?
There is no single statutory date on which year-end tax planning must begin. For many calendar-year businesses, late summer is a useful starting point: several months of actual results are available while time remains before the tax year closes. A typical sequence: August establish the YTD baseline · September revisit income and estimated-tax assumptions · October incorporate finalized extended-return information · November build a fuller federal and California projection · December identify remaining transactions and documentation.
1. August — Establish the Year-to-Date Baseline
August works as a starting point because businesses generally have more than half a year of operating information. The objective is not a final tax conclusion, but a more basic question: is the year-to-date accounting reliable enough to support a projection? Areas commonly reviewed include year-to-date revenue, operating expenses, payroll, receivables and payables, owner transactions, financing activity, fixed-asset additions and dispositions, and estimated payments already recorded. The IRS generally requires businesses to keep records supporting income, expenses, and credits reported on returns.
What information is still incomplete before a reliable full-year projection can be prepared? See the Mid-Year Tax Check-Up 2026, Bookkeeping Cleanup Before Year-End 2026, and Fixed Asset Review & California Depreciation Planning 2026 for the underlying detail.
2. September — Revisit Projections Around Estimated Taxes
September introduces a significant federal estimated-tax checkpoint: for calendar-year individuals required to pay estimated tax, the third federal installment for 2026 is due September 15, 2026. This is a natural point for pass-through owners and others with changing income to compare actual results with earlier assumptions — revenue above/below plan, expense changes, investment income, new income sources, owner compensation or distributions, and asset purchases or dispositions.
California uses a different regular installment pattern: 30% / 40% / 0% / 30%. The third California installment date is September 15, but the regular installment percentage is 0%.
This does not make September irrelevant for California. A change in projected California income may still affect the remaining annual liability or later payments. See Quarterly Estimated Taxes 2026 and California Estimated Tax Payments 2026 for the safe-harbor mechanics.
3. October — Connect the Prior-Year Return With Current-Year Planning
For taxpayers who obtained a timely extension, the general federal extended filing deadline for 2025 individual returns is October 15, 2026, and California generally provides an automatic six-month extension through the same date. The extension relates to filing time — it generally does not extend the deadline to pay. Finalizing the return can clarify previously provisional items: capital-loss carryforwards, depreciation schedules, state adjustments, entity tax information, basis, and prior-year figures used in estimated-tax calculations.
The October question: did the completed 2025 return reveal information that changes the 2026 planning file? See Tax Extensions 2026.
4. November — Build the Full-Year Projection
By November, most calendar-year businesses have a larger share of actual 2026 activity available, making it better suited to move from a year-to-date review toward a projected year-end result. A November projection commonly reviews:
| Area | Key planning question |
|---|---|
| Revenue | Has expected full-year revenue materially changed? |
| Expenses | Are recurring and significant expenses reflected through year-end? |
| Owner activity | Are distributions, contributions, and loans documented? |
| Estimated taxes | Do recorded payments align with the updated projection? |
| Fixed assets | Are additions and dispositions recorded accurately? |
| California adjustments | Are known state differences tracked separately? |
| Open items | What remains unresolved before December? |
This is where California business tax planning may require a distinct state calculation rather than relying only on the federal projection, because California does not conform to every federal rule. See California Conformity & Nonconformity 2026.
5. December — Separate Year-End Activity From Filing-Season Work
December is the final month of the calendar tax year, but December 31 is not a universal deadline for every tax-related action. Some consequences depend on transactions or events occurring during 2026 (income recognition, certain expense payments, completed asset transactions, property placed in service, payroll, charitable transfers, owner or related-party transactions). Others — receipt of W-2s, 1099s, and K-1s, final bookkeeping adjustments, return preparation, reconciliation of payments, and certain return-level elections — continue into filing season. A later filing deadline does not necessarily extend a separate substantive deadline requiring an event before December 31.
Timeline at a Glance
| Period | Primary focus | Key question |
|---|---|---|
| August | YTD accounting baseline | Is the information complete enough to project year-end results? |
| September | Estimated-tax checkpoint | Do earlier income and payment assumptions still hold? |
| October | Extended-return reconciliation | Did the finalized 2025 return change any 2026 assumptions? |
| November | Full-year projection | What does the federal and California year-end position look like? |
| December | Calendar-year close | Which transactions or records need attention before Dec 31? |
| January 2027 | Filing-season transition | What remains pending, and what filings come next? |
For business owners in Los Angeles, year-end planning generally combines federal rules with California-specific adjustments in a single process — not a separate local income-tax system. For broader service information, see Tax Planning in Los Angeles.
Compliance Resources and Tools
- Internal Revenue Service — Estimated Taxes and Form 1040-ES (2026) (accessed August 19, 2026).
- Internal Revenue Service — Extensions of Time to File (accessed August 19, 2026).
- California Franchise Tax Board — Estimated Tax Payments and Extension to File (accessed August 19, 2026).
- Year-end tax planning 2026 is a multi-month process, not a single December event.
- August establishes the financial baseline needed for later projections.
- September is a federal estimated-tax checkpoint and a moment to reassess assumptions.
- October connects finalized prior-year tax information with the current-year planning file.
- November suits a fuller federal and California year-end projection.
- December focuses on calendar-year transactions and documentation, separate from filing-season work.
- California businesses may need separate state calculations due to nonconformity.
References
- Internal Revenue Service. Estimated Taxes. irs.gov (accessed August 19, 2026).
- Internal Revenue Service. About Form 1040-ES, Estimated Tax for Individuals (2026). irs.gov/forms-pubs/about-form-1040-es (accessed August 19, 2026).
- Internal Revenue Service. Need more time to file? Request an extension. irs.gov (accessed August 19, 2026).
- California Franchise Tax Board. Estimated Tax Payments. ftb.ca.gov (accessed August 19, 2026).
- California Franchise Tax Board. Extension to File. ftb.ca.gov (accessed August 19, 2026).
The information contained in this publication is provided for educational and general informational purposes only. It does not constitute tax advice, accounting advice, legal advice, or any other form of professional advice and does not create a client-professional relationship.
The content reflects tax law and regulations applicable on the date of publication only and is subject to change without notice. Examples and illustrations are hypothetical and do not represent any specific taxpayer situation. Past results or referenced positions do not guarantee future outcomes.
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