2026 Year-End Tax Planning for Illinois Business Owners: Seven Decisions to Make Before December 31

Year-end planning is not about reading a list of every new tax law. It is about identifying the decisions that are still actionable before December 31, estimating their federal and Illinois effects, and completing the right steps while time remains.

For Illinois year-end tax planning in 2026, seven decisions deserve particular attention. They are especially relevant to S corporations, partnerships, and closely held C corporations managing owner compensation, equipment spending, retirement contributions, or a possible liquidity event.

At a glance: seven decisions to review

1. Recalculate federal and Illinois estimated payments.
2. Model the expanded Illinois PTE-tax calculation methods.
3. Account for Illinois’ different treatment of federal bonus depreciation.
4. Coordinate owner compensation, distributions, and retirement contributions.
5. Time equipment purchases and other deductible expenditures.
6. Evaluate QSBS exposure before selling startup stock.
7. Complete bookkeeping and reconcile owner activity before year-end.

The right answer depends on the taxpayer. A deduction that improves the federal result, for example, may not produce the same cash-tax benefit in Illinois.

1) Recalculate federal and Illinois estimated payments

Decision: Do you need to increase withholding or make another estimated payment to reduce underpayment penalties and avoid a large balance due?

For federal individual income tax, the required annual payment is generally the smaller of 90% of expected current-year tax or 100% of the tax shown on the prior-year return. The prior-year percentage generally increases to 110% when prior-year adjusted gross income exceeded $150,000, or $75,000 for married taxpayers filing separately. The rules include exceptions, so use the current IRS Publication 505 and your actual return information when calculating the payment.

Illinois business owners may also have payments running through the entity level. An Illinois partnership filing Form IL-1065 or S corporation filing Form IL-1120-ST that elects pass-through entity tax generally must make quarterly estimated payments when its expected replacement tax plus PTE tax liability, net of permitted credits and withholding, exceeds $500. Illinois generally sets those installments on the 15th day of the fourth, sixth, ninth, and twelfth months of the tax year. The Illinois Department of Revenue’s business estimated-payment guidance explains the threshold and timing.

Practical year-end moves

• Update year-to-date profit, owner wages, distributions, capital gains, and other significant personal income.
• Compare projected payments with the applicable federal safe harbor and the Illinois individual and entity requirements.
• Ask whether additional wage withholding or another estimated payment is the better way to address a projected shortfall.
• If the entity elected Illinois PTE tax, confirm that the election, calculation method, and payment schedule remain aligned.

2) Model the expanded Illinois PTE-tax calculation methods

Decision: If your business is taxed as a partnership, which Illinois PTE-tax base method produces the intended partner-level result?

For tax years ending on or after December 31, 2026, an electing partnership may choose between two methods for determining its Illinois PTE-tax base:

1. the Illinois-sourced portion of every partner’s distributive share; or
2. the full distributive shares of Illinois resident partners plus the Illinois-sourced distributive shares of nonresident partners.

The partnership selects its method on Form IL-1065. The choice can affect the entity’s estimated payments and the credit available to individual partners, particularly when resident and nonresident ownership is mixed. The Illinois Department of Revenue explains the new methods and transition relief in Informational Bulletin FY 2027-01.

Practical year-end moves

• Model both methods before finalizing year-end distributions and payments.
• Review each partner’s residency and Illinois-source income assumptions.
• Confirm that partner-level estimated payments reflect the expected PTE-tax credit.
• Document the selected method and the data supporting the calculation.

3) Account for Illinois’ different treatment of federal bonus depreciation

Decision: If the business claims federal bonus depreciation, what Illinois adjustment and cash-tax effect will follow?

Federal and Illinois depreciation will not always move together. Federal law generally restored a 100% special depreciation allowance for qualifying property acquired and placed in service after January 19, 2025. For tax years beginning on or after January 1, 2026, however, Illinois decouples from federal 100% bonus depreciation claimed under IRC Section 168(n).

That difference can create an Illinois addition or subtraction schedule that continues beyond the purchase year. The state’s FY 2026-15 income-tax bulletin describes the 2026 change, and the Illinois Form IL-4562 instructions explain how Illinois special-depreciation modifications are calculated.

Practical year-end moves

• Run a combined federal and Illinois projection before placing a major asset in service.
• Preserve acquisition dates, invoices, financing documents, and placed-in-service support.
• Update the fixed-asset schedule for current-year additions and disposals.
• Forecast the future Illinois subtraction pattern instead of focusing only on the current federal deduction.

4) Plan compensation, distributions, and retirement contributions together

Decision: Is owner compensation supportable, and do year-end payroll and retirement decisions work together?

An S corporation generally must pay a shareholder-employee reasonable compensation for services before making nonwage distributions to that person. The IRS may reclassify distributions or other payments as wages when the facts show they were compensation. Its S corporation compensation guidance identifies factors such as duties, time devoted to the business, experience, and comparable pay.

Compensation also affects retirement planning. For 2026, the employee elective-deferral limit for many 401(k) plans is $24,500, with a general age-50 catch-up of $8,000 and a higher $11,250 catch-up for eligible participants ages 60 through 63. The overall defined-contribution limit is generally $72,000 before applicable catch-up contributions. Review the current IRS 401(k) and profit-sharing limits and the rules of the specific plan.

For an S corporation shareholder, retirement contributions are based on Form W-2 compensation rather than distributions. Some employee deferral elections and payroll steps must be completed before year-end, while employer contribution deadlines can vary by plan and filing deadline.

Practical year-end moves

• Document the role, time commitment, responsibilities, experience, and comparable compensation supporting owner wages.
• Review remaining payroll dates before changing wages or employee deferrals.
• Coordinate cash needs for payroll taxes, retirement contributions, estimates, and distributions.
• Verify plan-specific limits and deadlines with the plan administrator before processing the final payroll.

5) Time equipment purchases and other deductible expenditures

Decision: Should the business acquire and place equipment in service before December 31, or is a later date better?

The purchase date alone does not determine depreciation. Property generally must be ready and available for its intended business use to be considered placed in service.

For tax years beginning in 2026, the federal Section 179 deduction limit is generally $2.56 million and begins to phase out when eligible property placed in service exceeds $4.09 million. Eligibility, taxable-income limits, business-use requirements, and special rules can reduce the available deduction. IRS Publication 946 summarizes the federal Section 179 and special-depreciation rules.

The strongest federal deduction is not automatically the best overall result. Illinois’ separate bonus-depreciation calculation, future income expectations, financing costs, and the actual business need for the asset all matter.

Practical year-end moves

• Confirm when the equipment will actually be installed, tested, and available for use.
• Compare Section 179, federal bonus depreciation, and regular depreciation.
• Include the Illinois Form IL-4562 effect in the same model.
• Avoid accelerating a purchase solely for a deduction when the asset or financing does not make business sense.

6) Evaluate QSBS exposure before selling startup stock

Decision: Could a planned stock sale qualify for the federal Qualified Small Business Stock exclusion, and what happens on the Illinois return?

Federal QSBS treatment under IRC Section 1202 is technical. Among other requirements, it generally applies to qualifying original-issue stock of an eligible domestic C corporation held by a noncorporate taxpayer. The holding period, acquisition date, issuer’s gross assets, active-business use, stock issuance, and transaction structure can all affect eligibility.

Federal legislation enacted July 4, 2025, added a phased exclusion for qualifying stock acquired after that date: 50% after at least three years, 75% after at least four years, and 100% after at least five years. Those new shorter holding periods cannot yet be satisfied during 2026, but the rules may affect planning for newer investments. See Public Law 119-21, Section 70431 and the IRS discussion of QSBS and Section 1045 rollovers in Publication 550.

Illinois now creates a major state-level difference. For tax years ending on or after December 31, 2026, individuals, trusts, estates, and partnerships generally must add back federally excluded Section 1202 gain when calculating Illinois base income. The federal exclusion therefore may not produce a matching Illinois exclusion. Illinois Informational Bulletin FY 2027-01 describes that decoupling.

Practical year-end moves

• Assemble stock-purchase documents, capitalization records, tax returns, and evidence supporting the issuer’s active business.
• Review QSBS eligibility before signing a letter of intent or purchase agreement.
• Model federal and Illinois results separately.
• If a sale is approaching, ask whether a Section 1045 rollover is available; its replacement-stock window is generally only 60 days.

7) Complete bookkeeping and reconcile owner activity before year-end

Decision: Are the books reliable enough to support the tax-planning calculations above?

Tax planning for Illinois business owners depends on timely accounting. Estimated taxes, PTE-tax methods, reasonable compensation, retirement contributions, depreciation elections, and shareholder or partner basis cannot be modeled well from incomplete or unreconciled records.

Practical year-end moves

• Reconcile every bank, credit-card, and loan account through the latest available statement.
• Resolve uncategorized transactions and confirm that personal activity is not buried in operating expenses.
• Tie payroll reports to the general ledger and reconcile payroll liabilities.
• Update fixed assets for additions, disposals, trade-ins, and placed-in-service dates.
• Review shareholder loans, partner contributions, distributions, and owner draws.
• Identify missing Forms W-9, contractor payments, and other information-reporting items before January deadlines.

If the accounting needs attention, Basso CPAs’ bookkeeping and monthly-close services can help establish the clean financial information required for sound planning.

Turn the analysis into an action list

The value of year-end planning comes from sequencing. Update the books first, project federal and Illinois liabilities, identify decisions with real deadlines, and assign each action to the owner, payroll provider, plan administrator, attorney, or tax professional responsible for completing it.

For help evaluating these decisions, learn more about tax-planning services from Basso CPAs or schedule a conversation before transactions and deadlines narrow the available options.

Important: This article is for general informational purposes only. It is not tax, legal, investment, or financial advice. Every individual and business has different facts and circumstances, and tax laws can change. Before acting, verify how these rules apply to you with your CPA, tax advisor, financial advisor, or attorney, as appropriate.

Primary sources

• IRS Publication 505 (2026), Tax Withholding and Estimated Tax
• IRS guidance on S corporation compensation
• IRS 2026 401(k) and profit-sharing plan contribution limits
• IRS Publication 946, How To Depreciate Property
• IRS Publication 550, Investment Income and Expenses
• Public Law 119-21, Section 70431, expansion of the federal QSBS exclusion
• Illinois Department of Revenue, Business Income Tax Estimated Payments
• Illinois Department of Revenue, FY 2026-15, What’s New for Illinois Income Taxes
• Illinois Department of Revenue, FY 2027-01, 2026 Income Tax Changes
• Illinois Department of Revenue, Form IL-4562 Instructions