S-Corp Year-End Tax Planning Checklist: December Action Items

December 31 is a hard deadline. Once it passes, many S-Corp tax strategies disappear.

Equipment deductions? The asset must be in service by year-end. 401(k) deferrals? December 31, no exceptions. Salary adjustments? Final payroll must process before the calendar turns.

This checklist covers every year-end action item for S-Corp owners. Use it to make sure nothing falls through the cracks.

Key Takeaways

• 401(k) employee deferrals must happen by December 31—no exceptions, no extensions
• Equipment must be purchased AND placed in service by year-end for Section 179 deduction
• Finalize reasonable salary through final payroll before the calendar turns
• Employer retirement contributions have more flexibility—can wait until tax filing deadline
• Start planning in October, not December 30—many moves require lead time

Why Year-End Planning Matters for S-Corps

Tax planning works best when it’s proactive. But reality hits: most business owners start thinking about taxes in December. That’s not ideal, but it’s recoverable if you move quickly.

What Can Still Be Done in December:

• Equipment purchases (placed in service, not just ordered)
• Retirement contributions (employee deferrals must happen by Dec 31)
• Salary adjustments (run final payroll before year-end)
• Expense reimbursements (submit and pay before books close)
• State tax elections (check PTET deadlines)

What Can’t Be Done After December 31:

• 401(k) employee deferrals for the tax year
• Section 179 deductions for equipment not in service
• W-2 salary increases for the prior year

The stakes are real. Missing a deadline can cost thousands in lost deductions.

For a comprehensive overview of S-Corp taxation, see our S-Corporation Tax Guide.

Review and Finalize Reasonable Salary

Your W-2 salary affects multiple things: FICA taxes, QBI wage limitations, and IRS compliance. Year-end is the time to make sure it’s right.

Year-End Salary Checklist:

☐ Review YTD salary against market benchmarks Pull comparable salary data from BLS, Glassdoor, or industry surveys. Confirm your salary is defensible if questioned.

☐ Ensure final payroll processes by December 31 Check your payroll calendar. If your last payroll of the year is mid-December, consider whether an additional payroll or bonus is warranted.

☐ Document salary determination rationale Create or update your salary justification memo. Include comparable salary data, your duties, hours worked, and any changes from prior year.

☐ Verify payroll tax deposits are current Late deposits create penalties. Confirm all deposits have been made per your deposit schedule.

☐ Consider a year-end bonus if salary seems low If your YTD salary appears low relative to benchmarks, a year-end bonus (processed as payroll) can bring it to an appropriate level.

For detailed guidance on compensation, see S-Corp Reasonable Compensation Guide.

Maximize Retirement Contributions

Retirement contributions are the most powerful year-end tax tool. But timing matters.

Retirement Year-End Checklist:

☐ 401(k) employee deferrals: MUST be made by December 31 There is no extension. If you want to defer $24,500 for 2026, that money must come out of your December paycheck or earlier.

☐ Calculate maximum allowable deferral 2026 limits:

• Standard: $24,500
• Catch-up (age 50+): Additional $8,000
• Catch-up (age 60-63): Additional $11,250

☐ Employer contributions: Can wait until tax deadline Profit-sharing contributions can be made up to September 15, 2027 (with extension). But you need a plan in place by December 31 to contribute for that year.

☐ Review combined limit The 2026 combined limit (employee + employer) is $72,000, or up to $80,000+ with catch-up contributions.

☐ Consider catch-up contributions If you’re 50 or older, you’re leaving money on the table by not using catch-up contributions.

☐ SEP-IRA alternative If you don’t have a 401(k), a SEP-IRA can be established and funded up until your tax filing deadline, including extensions.

Critical deadline reminder: Employee deferrals must occur through payroll by December 31. Employer contributions have more flexibility.

For complete retirement planning guidance, see S-Corp Retirement & 401(k) Guide.

Equipment Purchases and Section 179

Section 179 allows immediate deduction of equipment costs, but timing rules are strict.

Equipment Year-End Checklist:

☐ Identify needed equipment purchases List equipment you’ve been considering: computers, software, machinery, vehicles, furniture.

☐ Calculate Section 179 availability 2026 limit: Approximately $1,320,000 Phase-out threshold: Approximately $3,290,000

☐ Equipment must be PURCHASED and IN SERVICE by December 31 This is critical. Ordering on December 30 with delivery January 5 does not qualify for 2026 deduction.

☐ Consider bonus depreciation for excess If you exceed Section 179 limits or have non-qualifying property, 60% bonus depreciation is available for 2026.

☐ Review vehicle limitations Heavy SUVs (over 6,000 lbs GVWR): Section 179 limited to approximately $30,500 Passenger vehicles: Subject to luxury auto limits

☐ Document placed-in-service date Keep records showing when equipment was received and first used.

Warning: “Placed in service” means ready and available for use. Buying equipment and leaving it in the box doesn’t count.

For complete Section 179 guidance, see Section 179 Deduction Guide.

Health Insurance and Fringe Benefits

S-Corp health insurance has specific reporting requirements that must be handled correctly.

Health Insurance Year-End Checklist:

☐ Verify 2%+ shareholder health premiums paid or reimbursed If your S-Corp pays or reimburses your health insurance premiums, this must be included in your W-2 wages.

☐ Confirm premiums added to W-2 (Box 1, not Box 3/5) Health insurance premiums for 2%+ shareholders are included in Box 1 (wages) but excluded from Box 3 (Social Security wages) and Box 5 (Medicare wages).

☐ Ensure HRA/QSEHRA compliance If using a health reimbursement arrangement, confirm it’s properly structured and documented.

☐ Review other fringe benefits for proper reporting Life insurance over $50,000, personal use of company vehicles, and other benefits have reporting requirements.

☐ Document company vehicle use if applicable If you have a company vehicle, track business vs. personal mileage. Personal use is a taxable fringe benefit.

For complete health insurance guidance, see S-Corp Health Insurance Rules for Owners.

Expense Reimbursement Through Accountable Plans

Business expenses you paid personally should be reimbursed by your S-Corp before year-end.

Expense Reimbursement Checklist:

☐ Submit all outstanding expense reports Go through credit card statements and bank records. Capture every legitimate business expense.

☐ Document business purpose for each expense Receipts alone aren’t enough. Note the business purpose, attendees (for meals), and client/project connection.

☐ Include mileage logs If you use a personal vehicle for business, maintain a mileage log with dates, destinations, and business purposes.

☐ Reimburse through payroll or corporate check Process reimbursements through your normal accounting. Keep records of payment.

☐ Deadline: Before year-end books close Reimbursements should occur in the same tax year as the expenses.

Accountable plan requirements:

• Business connection for all expenses
• Adequate documentation submitted
• Excess reimbursements returned

Properly structured reimbursements are tax-free to you and deductible by the S-Corp.

Verify Estimated Tax Payments

As a pass-through entity, S-Corp income flows to your personal return. You need to make quarterly estimated payments.

Estimated Tax Checklist:

☐ Review Q4 estimated payment (due January 15) Your Q4 payment for 2026 is due January 15, 2027. Don’t forget this falls after year-end.

☐ Calculate safe harbor To avoid underpayment penalties, pay at least:

• 100% of prior year tax, OR
• 110% of prior year tax if AGI exceeded $150,000

☐ Consider catch-up payment if short If you’re behind on estimates, an increased Q4 payment reduces penalties.

☐ Verify state estimated payments as well Many states have their own estimated tax requirements. Check your state’s rules.

For deadline information, see S-Corp Tax Deadlines & Filing Requirements.

Review Shareholder Basis

Distributions that exceed your basis are taxable as capital gains. Losses that exceed basis are suspended.

Basis Review Checklist:

☐ Calculate current basis position Start with beginning basis, add income and capital contributions, subtract losses and distributions.

☐ Factor in income, losses, distributions YTD Use your year-to-date financials to estimate where basis stands.

☐ Ensure planned distributions won’t exceed basis If you’re taking a large distribution, confirm you have sufficient basis.

☐ Consider year-end capital contribution if needed A capital contribution increases basis, potentially allowing tax-free distributions or loss deductions.

For distribution rules, see S-Corp Distributions Tax Rules.

Corporate Formalities Checklist

Maintaining corporate formalities protects your liability shield and supports your entity’s legitimacy.

Year-End Formalities Checklist:

☐ Hold annual meeting or document consent resolution Even if you’re the sole shareholder, document your annual meeting in minutes or a written consent.

☐ Document major decisions Salary determinations, large purchases, and distribution decisions should be documented.

☐ Update operating agreement if needed If circumstances have changed (new ownership percentages, different roles), update your governing documents.

☐ File annual state report/franchise tax if required Many states require annual reports or franchise tax filings. Check your state’s requirements and deadlines.

☐ Verify S-Corp election status is intact Certain events can terminate S-Corp status: ineligible shareholders, more than 100 shareholders, or issuing a second class of stock. Confirm nothing has changed.

Year-End Tax Planning Timeline

Frequently Asked Questions

What tax moves should I make before year-end?

Focus on: finalizing reasonable salary through final payroll, making 401(k) deferrals, purchasing and placing equipment in service, submitting expense reimbursements, and reviewing estimated payments. These items have hard December 31 deadlines.

Can I maximize deductions after December 31?

Some items have flexibility. Employer retirement contributions can be made until your tax filing deadline. SEP-IRAs can be established and funded by the deadline. But employee deferrals, equipment in-service dates, and W-2 wages are locked to the calendar year.

When must 401(k) contributions be made?

Employee deferrals must be made by December 31. There are no exceptions or extensions. Employer contributions (profit sharing) can be made up to the tax filing deadline, including extensions.

What’s the Section 179 deadline?

Equipment must be purchased AND placed in service by December 31. “Placed in service” means available and ready for use, not just ordered or received in packaging.

How do I handle S-Corp health insurance at year-end?

Ensure premiums paid or reimbursed for 2%+ shareholders are included on the shareholder’s W-2 in Box 1. Process the W-2 adjustment before issuing year-end W-2s.

What corporate formalities are required annually?

At minimum: annual meeting (or written consent), documentation of major decisions, state annual report filing if required, and maintaining records that support your corporate status.

Start Now, Not December 30

The best year-end tax planning happens in October or November, not the last week of December. Equipment takes time to purchase and receive. Payroll changes need to be communicated. Retirement elections require paperwork.

But even if you’re reading this in mid-December, there’s still time to act. Just don’t wait another day.

If you’d like help reviewing your S-Corp’s year-end position or ensuring you’re capturing every available deduction, schedule a year-end planning session. We work with S-Corp owners across industries and can help you close out the year strategically.

For more on S-Corp taxation and planning, visit our S-Corp Tax Services page.