Year-End Tax Planning Checklist for Business Owners

October is your gateway to tax optimization. With 92 days remaining in the tax year, you have sufficient time to implement major strategies. The IRS requires 90 days' notice for certain entity elections, meaning October decisions directly affect your December 31st year-end position.

The three critical October moves are: (1) estimating final Q4 income, (2) reviewing estimated tax payments to avoid penalties, and (3) planning for expense acceleration or income deferral based on projected taxable income.

November is execution month. The strategic decisions from October now become concrete actions. This is when you finalize expense acceleration, complete S-corporation elections, and implement retirement plan contributions before the December 31st deadline.

Expense Acceleration Opportunities

Under IRC Section 162, ordinary and necessary business expenses reduce taxable income dollar-for-dollar. If you accelerate $100,000 in business expenses to November, you reduce 2026 taxable income by $100,000, saving approximately $35,000 in federal, state, and self-employment taxes (combined 35% effective rate).

December is the deadline month. Every action taken by December 31st at 11:59 PM is tax-deductible in 2026. The IRS enforces a strict bright-line rule: transactions after midnight on December 31st belong to 2027. This creates both urgency and opportunity for last-minute tax optimization.

December 31st Deadline Items

Entity structure is the single most impactful tax decision for profitable businesses. The self-employment tax savings alone (15.3% on business income reduction) often exceeds the cost of accounting complexity. An S-corporation election can save 15.3% on 60% of business income, or 9.2% total tax reduction.

Entity Comparison Analysis

The S-corporation election is optimal for service businesses earning $80,000+ annually. Below $80,000, accounting complexity outweighs tax savings. The IRS expects reasonable W-2 wages in S-corporations, typically 50 to 60% of net business income, to prevent aggressive income splitting.

Estimated tax penalties accumulate as interest, not a flat fee. The rate is the federal short-term rate plus 3 percentage points, compounded daily, and it resets every quarter (it ran 6 to 7 percent through 2026). This is a real tax cost, not deductible against income, that is entirely avoidable with proper calculation.

2026 Estimated Tax Worksheet

Bonus depreciation (IRC Section 168(k)) allows a 100% first-year deduction for qualified property placed in service in 2026. Under the 2025 tax law (OBBBA), 100% bonus depreciation is now permanent for qualified property acquired and placed in service after January 19, 2025, rather than the phase-down schedule that applied under prior law. This is the most aggressive depreciation method available under the tax code and converts capital purchases into immediate operating expenses.

Bonus Depreciation vs. Section 179

Cost segregation is a specialized technique that breaks down buildings into components with shorter depreciation periods. A $2M building purchase might be reclassified as 40% components (7-year property) vs 60% building (39-year property). This accelerates deductions by $50,000 to $150,000 depending on property composition.

Retirement plan contributions are the most tax-efficient savings mechanism available. You receive an immediate tax deduction (reduces taxable income) while building tax-deferred wealth. The plan establishment deadline is December 31, 2026; there is no extension on that date.

Plan Selection Guide

Tax planning without documentation is a liability, not a benefit. The IRS requires contemporaneous written evidence for deductions. This is especially critical for aggressive strategies like bonus depreciation, S-corporation elections, and entertainment expenses.

Essential Tax Records to Maintain

Your Year-End Action Checklist

The decisions you make in October, November, and December directly impact your 2026 tax liability. A business owner who implements all strategies in this checklist can reduce taxable income by $200,000 to $500,000, saving $70,000 to $175,000 in taxes.

If this checklist feels like more than you want to run alone, the highest-leverage move is to find a tax strategist before year-end, while the December deadlines above can still be met.