How to Execute Year-End Tax Planning for Business Clients Before December 31

The last 90 days of the calendar year are the highest-leverage window in tax practice. Most decisions that materially affect a client's 2025 tax bill — entity elections, salary adjustments, equipment purchases, retirement contributions, Roth conversions — must be completed before December 31. After that date, options collapse: you can file an extension, but you cannot retroactively place equipment in service, convert a traditional IRA, or elect S-Corp status for a year that has already ended. This guide covers the ten highest-impact strategies CPAs should sequence with business clients before year-end, in the order they should be executed.

Prerequisites

Current-year income projection available or estimable from YTD financials
Pass-through entity clients using S-Corp, partnership, or sole proprietorship structure
Access to client's prior-year return and current-year estimated tax payments made to date
BLS Occupational Employment and Wage Statistics data for S-Corp salary reviews (bls.gov/oes)
Retirement plan documents for clients with SEP-IRAs, SIMPLE IRAs, or 401(k) plans

Step 1: Run the S-Corp Election Analysis for the Following Year

For clients operating as single-member or multi-member LLCs without S-Corp election, year-end is the natural decision point for whether to elect for the following tax year. Form 2553 must be filed by March 15 of the tax year it takes effect — but the analysis belongs in Q4, while full-year income data is available to project actual savings. For the complete 2025 filing deadline calendar for 1120-S, 1065, and 1120 returns — including extension rules, K-1 furnishing obligations, and per-entity penalty structures — see Business Tax Return Deadlines 2025.

The breakeven for S-Corp election sits between $60,000 and $70,000 in net profit for most clients. Above that level, the self-employment tax savings (avoiding 15.3% FICA on distributions above a reasonable salary) typically outpace the $1,500–$4,000 annual compliance overhead of payroll, Form 1120-S preparation, and reasonable salary documentation. Below it, costs routinely exceed savings.

Run the analysis with actual year-to-date numbers and a full-year projection. If income is clearly above the breakeven, prepare Form 2553 for the client's review and timely submission. For the complete tax savings model, compliance cost breakdown, state-specific considerations, and a side-by-side comparison of each structure, see S-Corp vs LLC: Which Tax Structure Saves More in 2025?. For clients where C-Corp may be more appropriate than S-Corp — QSBS eligibility, retained earnings accumulation, or institutional investment plans — see C-Corp vs S-Corp vs LLC: The Complete Entity Selection Guide for CPAs for the three-way decision framework.

State tax note: California clients with net income between $60,000 and $120,000 often find that the 1.5% franchise tax plus $800 minimum franchise fee erases the federal advantage. Model state taxes explicitly before recommending conversion for clients in California, New York City, or Tennessee.

ACA employer mandate check: For clients with growing headcount — particularly those approaching 50 full-time equivalent employees — year-end is also the right moment to run the ACA applicable large employer (ALE) calculation. A business that averages 50+ FTEs during 2025 becomes an ALE for all of 2026, subject to the employer mandate's coverage offer requirements and §4980H penalties. This analysis belongs alongside the S-Corp election review because both involve the prior-year FTE count and both have January planning implications. See ACA Employer Mandate: The 50-Employee Threshold, Coverage Requirements, and Penalties Explained for the FTE counting methodology and penalty modeling framework.

Step 2: Lock In the S-Corp Reasonable Salary Before Year-End

For existing S-Corp clients, year-end is the last opportunity to correct or update the owner-employee's W-2 salary for the current tax year. If salary has been running below a defensible market rate, a year-end payroll catch-up can bring compensation into line with Bureau of Labor Statistics (BLS) OEWS figures before December 31.

Two situations require immediate action:

Salary too low: A salary of $40,000 against $300,000 in distributions produces a distribution-to-salary ratio of 7.5:1 — a standard IRS audit trigger. A year-end payroll adjustment can correct this, but the payment must actually be processed and deposited via payroll before December 31. Board minutes alone do not establish the wage payment.
Salary unchanged for multiple years: BLS OEWS data updates annually; a salary set three years ago at the 50th percentile may now be well below the current survey year's figures. Run updated BLS data and formally re-adopt the salary in board minutes.

For the full methodology — BLS data lookup, IRS reasonableness factors (training, duties, scope, compensation history), distribution-to-salary ratio stress testing, and board minute sample language — see How to Calculate and Document a Reasonable S-Corp Salary.

Payroll timing: W-2 wages paid in January for December work are reported on the next year's W-2. Any catch-up compensation for the current tax year must clear payroll before December 31.

Step 3: Model the QBI Deduction and Manage Phase-Out Exposure

The Section 199A Qualified Business Income deduction — made permanent by the One Big Beautiful Bill Act (OBBBA) — allows eligible pass-through owners to deduct up to 20% of net business income, reducing the effective top marginal rate from 37% to 29.6%. For clients whose taxable income approaches the phase-out thresholds ($197,300 single / $394,600 MFJ in 2025 per IRS Rev. Proc. 2024-40), year-end is the time to project exposure and act.

Two restrictions phase in above the threshold:

For all qualified businesses: The W-2 wage limitation — the QBI deduction is capped at the greater of (a) 50% of W-2 wages paid by the business, or (b) 25% of W-2 wages plus 2.5% of the unadjusted basis of qualified depreciable property (IRC §199A(b)(2)(B))
For specified service trade or business (SSTB) clients — physicians, attorneys, accountants, consultants, financial advisors — the deduction phases out entirely above $247,300 (single) / $494,600 (MFJ)

Year-end levers:

Retirement plan contributions: A high-income SSTB client who contributes $69,000 to a defined benefit plan or solo 401(k) profit-sharing account before December 31 reduces taxable income by that amount — potentially pulling them below the phase-out range entirely
S-Corp salary adjustment: For non-SSTB clients above the threshold, increasing W-2 salary increases the W-2 wage limitation cap. Above the Social Security wage base ($176,100 in 2025), additional salary costs only 2.9% in Medicare FICA but increases the QBI deduction cap by $0.50 — worth $0.185 per dollar at the 37% marginal rate; net positive
Timing deductions: Accelerating deductible business expenses into the current year reduces taxable income and the QBI phase-out exposure. Prepaying annual insurance premiums before December 31 is one commonly used application — the 12-month prepayment rule at Treas. Reg. §1.263(a)-4(f) allows cash-basis taxpayers to deduct a full annual premium in the current year when the coverage period does not extend beyond December 31 of the following year. For accrual-basis clients, the recurring item exception under IRC §461(h)(3) provides a parallel mechanism with broader application: liabilities incurred by December 31 are deductible in the year of accrual if economic performance occurs within 8.5 months after year-end — covering accrued bonuses, professional fees, and other year-end payables that cash basis defers until payment. For the full mechanics of both methods, including the §481(a) adjustment analysis for clients considering a switch, see Switching from Cash Basis to Accrual Accounting: Tax Implications Every CPA Must Know. For the deductibility rules across coverage types and the documentation requirements, see Business Insurance Premium Tax Deductions: What's Deductible, What Isn't, and How to Document It

For the full W-2 wage limitation calculation, the salary-versus-distribution QBI tradeoff model, and SSTB planning scenarios, see QBI Deduction in 2025: How Section 199A Works After OBBBA.

Step 4: Execute Year-End Equipment Purchases and Confirm Placed-in-Service Status

With 100% bonus depreciation restored for 2025 under OBBBA, and the Section 179 expensing limit at $1,250,000 (IRS Rev. Proc. 2024-40, with a phase-out beginning at $3,130,000), Q4 is the primary window for equipment planning. A $200,000 equipment purchase placed in service before December 31 generates a $200,000 federal deduction in the current year — reducing taxable income at the client's marginal rate, immediately.

Two timing points require explicit attention at year-end:

Placed-in-service requirement: Equipment must be in a condition and state of readiness for its intended use by December 31 (IRC §168(k)). Ordered, paid for, and sitting in a warehouse does not qualify. Confirm delivery, installation, and operational readiness before year-end. The IRS focuses on when the asset is available for its intended business purpose — not when the purchase order was signed or the invoice paid.

State tax decoupling: California, New Jersey, and Massachusetts do not conform to 100% federal bonus depreciation. A California client who fully expenses $500,000 in equipment federally still owes California tax on that income in year 1, recovering it through regular MACRS over 5–7 years. Model the current-year state tax bill explicitly before recommending full federal expensing in high-decoupling states — the surprise state tax bill is the most common objection CPAs face after recommending bonus depreciation without state modeling.

For the complete qualification rules, election sequencing methodology (Section 179 before bonus), the state decoupling table, and the interaction with the QBI deduction's Method 2 property test, see How to Apply Bonus Depreciation and Section 179 for Business Clients in 2025.

Step 5: Maximize Retirement Plan Contributions

Retirement plan contributions reduce taxable income dollar-for-dollar. The IRS sets annual limits that expire at year-end (or at the tax return's extended due date for employer contributions to certain plan types); unused capacity does not carry forward.

2025 contribution limits (IRS Rev. Proc. 2024-40):

Plan Type	Employee Deferral	Employer Contribution	Total Annual Limit
Solo 401(k)	$23,500 ($31,000 age 50+)	25% of W-2 wages	$70,000 ($77,500 age 50+)
SEP-IRA	N/A	25% of W-2 wages / 20% of SE income	$70,000
SIMPLE IRA	$16,500 ($20,000 age 50+)	2% or 3% match	—
Defined Benefit Plan	N/A	Actuarially determined	Up to $275,000 benefit

Year-end checklist:

Confirm employee deferrals are maximized and deposited by December 31 for the current tax year
Calculate the maximum employer profit-sharing contribution and fund before December 31 (401(k)) or by the extended return due date (SEP-IRA)
For high-income SSTB clients near the Section 199A phase-out: defined benefit plan contributions can reach $275,000 or more annually and can pull taxable income below the SSTB exclusion threshold entirely
For S-Corp owners: solo 401(k) employee deferral and employer profit-sharing contributions are both based on W-2 wages, not net SE income — increasing year-end payroll per Step 2 can unlock additional contribution room

SECURE 2.0 Act provisions effective in 2025 introduced an enhanced catch-up contribution tier for plan participants aged 60–63, raising the 401(k) catch-up from $7,500 to $11,250 for this age group. A 2026 Roth catch-up requirement for high earners and mandatory auto-enrollment rules for new plans also require employer action before year-end. For the full schedule of effective dates, limit changes, and compliance deadlines, see SECURE 2.0 Act Retirement Plan Changes Every CPA Must Know for 2025–2026. For clients who don't yet have a plan, see SEP IRA vs SIMPLE IRA vs Solo 401(k): Choosing the Right Retirement Plan for Small Business Clients — including the critical December 31 Solo 401(k) establishment deadline and the SEP IRA's post-year-end flexibility.

Step 6: Evaluate Roth Conversion Opportunities

A Roth conversion — moving funds from a traditional IRA to a Roth IRA — is a year-end strategy for clients in years with temporarily low taxable income or large deductions. The converted amount is included in gross income in the year of conversion (IRC §408A(d)(3)). Recharacterization — reversing a Roth conversion — was eliminated by the TCJA and is no longer permitted.

When Roth conversion makes sense:

Taxable income for the current year is unusually low due to business losses, large deductible contributions, or retirement. If a business loss will generate or add to an NOL carryforward, coordinate the Roth conversion to shelter the converted amount with the NOL — but apply the 80% taxable income limitation correctly before projecting the offset. See Net Operating Loss (NOL) Carryforward Rules for CPAs for the mechanics.
The client expects higher marginal rates in future years — either through rising income or anticipated tax law changes
The client has sufficient non-IRA cash to pay the conversion tax without drawing from the converted funds

Partial conversions: Converting just enough to fill the current bracket — up to the 22% or 24% rate threshold — captures the rate differential without pushing income into a higher bracket. Calculating the exact conversion amount requires knowing current-year taxable income with precision before year-end.

QBI interaction: For SSTB clients near the Section 199A phase-out range, a Roth conversion that pushes taxable income above the threshold eliminates the QBI deduction — a cost that often exceeds the conversion's long-term benefit. Model the QBI impact alongside the conversion before recommending it.

CTC interaction: For clients with qualifying children whose MAGI is near the $400,000 MFJ / $200,000 single phase-out thresholds, a Roth conversion increases MAGI dollar-for-dollar, reducing the Child Tax Credit by $50 per child per $1,000 of excess MAGI. A $20,000 conversion for a two-child MFJ family sitting at $395,000 MAGI costs $500 in lost CTC in addition to the income tax on the converted amount. See Child Tax Credit 2025: Income Limits, Phase-Outs, and How to Maximize It for Clients for the complete phase-out math and strategies for managing MAGI around the threshold.

Custodian processing: Conversions must be completed and reflected on the account by December 31. Submit conversion requests by mid-December for most custodians; processing times vary.

For the complete conversion framework — pro-rata rule, bracket-filling math, IRMAA impact modeling, and Form 8606 filing requirements — see How to Advise Clients on Roth IRA Conversions.

Step 7: Harvest Capital Losses to Offset Gains

Tax-loss harvesting — selling depreciated investment positions before December 31 to realize losses that offset capital gains — is one of the most consistently available year-end tax opportunities. Capital losses offset capital gains dollar-for-dollar; up to $3,000 of excess losses offset ordinary income annually under IRC §1211(b).

The wash-sale rule (IRC §1091): A loss is disallowed if the taxpayer purchases substantially identical securities within 30 days before or after the sale, across all accounts including IRAs and spousal accounts. Clients can immediately repurchase a similar-but-not-identical fund (e.g., a comparable index fund from a different provider) to maintain market exposure without triggering the wash-sale rule.

Cryptocurrency loss harvesting: The wash-sale rule applies only to "stock or securities" under IRC §1091 — cryptocurrency is property under IRS Notice 2014-21, not a security, so the rule does not apply. A client who sells Bitcoin at a loss can immediately repurchase the same amount without any disallowance. This creates a year-end loss-harvesting opportunity in crypto positions that does not exist in equity portfolios: losses can be realized and the position immediately re-established with no 30-day waiting window. For the complete framework on cryptocurrency gain and loss recognition, cost basis methods, and Form 8949 reporting, see Cryptocurrency Tax Reporting for CPAs.

Settlement timing: Under SEC Rule 17a-3, equity trades now settle T+1. A trade executed on December 31 settles on January 2 — making it a next-year transaction. The effective last trading day for year-end settlement varies by asset class and exchange holiday schedule; verify custodian settlement deadlines in late November.

Business asset gains: For business clients with pass-through income, capital losses from investment portfolios can offset gains from business asset sales — including depreciation recapture on real estate disposals and Section 1231 gains on equipment sales. Model the full capital account, not just the investment portfolio. For real estate clients with significant unrealized appreciation, a 1031 like-kind exchange is often more powerful than loss harvesting — it defers the entire gain rather than offsetting a portion. See How to Execute a 1031 Like-Kind Exchange for Real Estate Clients for the complete mechanics, including the 45-day identification window, 180-day closing deadline, and basis computation.

Step 8: Accelerate Deductions or Defer Income Based on Bracket Projections

The decision to accelerate a deduction or defer income into the next year turns on which year carries the higher marginal rate. For clients with predictably stable income, the analysis is straightforward; for clients with income variability, it requires a projection now.

Accelerate deductions when this year's marginal rate is higher:

Prepay deductible business expenses before December 31: professional subscriptions, business insurance premiums (up to 12 months for cash-basis clients under the 12-month rule, Treas. Reg. §1.263(a)-4(f)), software licenses, association dues
Pay Q4 state estimated taxes due January 15 before December 31 — for clients not subject to the SALT deduction cap, this shifts the deduction into the current year. Pass-through entity owners subject to the cap have a more powerful alternative: a state-level PTE election allows the entity to pay state income tax and deduct it at the federal level, completely bypassing the $10,000 limit — see How to Use State PTE Tax Elections to Bypass the SALT Cap
Accelerate vendor payments for deductible supplies and services

Defer income when next year's marginal rate is lower:

For cash-basis businesses, delay sending December invoices until January — amounts not received by December 31 are not taxable until received
Defer December bonuses to a January payroll run (must reflect a genuine business decision; cannot function as a disguised distribution for S-Corp owners)
Delay the close of asset sales that would trigger taxable gain until the next tax year

Constructive receipt: Under IRC §451 and Treas. Reg. §1.451-1, income available to a cash-basis taxpayer without restriction is taxable when constructively received — not when physically deposited. A check received in December but held uncashed remains taxable in December.

Step 9: Optimize Charitable Giving

Three year-end charitable strategies can significantly increase tax efficiency for high-income business clients.

Qualified Charitable Distributions (QCDs): Taxpayers age 70½ or older may direct up to $108,000 (2025 limit, inflation-adjusted under IRC §408(d)(8)(B)) from a traditional IRA directly to a qualifying public charity. The distribution is excluded from gross income — reducing AGI regardless of whether the client itemizes — and satisfies the required minimum distribution (RMD) obligation. QCDs must be received by the charity by December 31. For clients who take the standard deduction, a QCD is almost always more tax-efficient than a cash contribution.

Charitable bunching: Clients who normally give $10,000–$15,000 per year and take the standard deduction ($15,000 single / $30,000 MFJ in 2025) can concentrate two or three years of contributions into a single tax year to exceed the standard deduction threshold — then return to the standard deduction in the following years. The total charitable impact is identical; the tax benefit is significantly higher. For the full decision framework — including which client profiles benefit from itemizing, how the SALT cap affects the analysis, and the complete bunching math — see Standard Deduction vs Itemized Deductions: How CPAs Decide for Clients in 2025.

Donor-Advised Funds (DAFs): A contribution of appreciated stock or cash to a DAF before December 31 generates a current-year charitable deduction (subject to AGI limits of 60% for cash, 30% for appreciated property), with no obligation to distribute to specific charities until later. For clients with a windfall year — business sale, large bonus, asset liquidation — a large DAF contribution locks in the deduction without requiring immediate charitable decisions. Contributed appreciated securities generate no capital gain recognition on the transfer.

Step 10: Reconcile and Finalize Estimated Tax Payments

The Q4 estimated tax payment is due January 15, but year-end is the time to reconcile the year's payments against projected liability — before the underpayment penalty calculates.

2025 estimated tax safe harbors (IRC §6654):

Prior-year safe harbor: Total payments equal 100% of prior-year tax liability (110% for clients with AGI above $150,000 in the prior year) — avoids underpayment penalties regardless of current-year actual liability
Current-year safe harbor: Total payments equal 90% of current-year actual tax — requires income projection accuracy and carries risk if Q4 income was underestimated

For clients who have underpaid through Q3, the Q4 payment (due January 15) can close the gap to the prior-year safe harbor amount. Calculate the shortfall from current-year actuals now.

W-2 withholding as a retroactive fix: For S-Corp owners running payroll, increasing W-2 federal withholding in the last December payroll run can substitute for — and in some cases surpass — a Q4 estimated tax payment. Under IRC §3402, W-2 withholding is treated as paid ratably throughout the year regardless of when it was actually withheld. A large December withholding catch-up cures underpayments from Q1 through Q3 that additional estimated payments cannot retroactively fix.

Annualization exception: Clients with highly seasonal income can avoid underpayment penalties by annualizing income on Form 2210, Schedule AI, and demonstrating that payments tracked actual income earned in each quarter. Useful for clients who earn the majority of income in Q4.

For the full estimated tax methodology — safe harbor calculations, EFTPS scheduling, state payment variations, and how bonus depreciation affects installment sizing — see How to Calculate and File Quarterly Estimated Taxes for Business Clients.

Common Mistakes

Acting on year-end strategies after December 31. Equipment must be placed in service; Roth conversions must be completed; salary adjustments must be processed via payroll; estimated tax payments must be made. Planning conversations that begin after December 15 may not leave enough time to implement all items, particularly those requiring custodian processing or payroll runs. Start the year-end review in October.

Running S-Corp salary analysis without QBI modeling. Increasing salary to satisfy the QBI W-2 wage limitation costs FICA. Decreasing salary to minimize FICA costs QBI deduction ceiling. These optimize in opposite directions. Never finalize an S-Corp salary without running the full combined FICA and QBI model — the correct salary is the one that minimizes total combined tax, not just payroll tax.

Ignoring state tax implications of bonus depreciation. 100% federal bonus depreciation in a California, New Jersey, or Massachusetts entity generates a current-year state income tax on the expensed amount, recoverable over the asset's MACRS life. Clients who see only the federal result are often surprised by Q1 state estimated tax notices the following year.

Triggering the wash-sale rule through IRA or spousal repurchases. The 30-day wash-sale window applies across all accounts in the taxpayer's household, including traditional and Roth IRAs and a spouse's taxable brokerage account. Clients with automatic dividend reinvestment plans must also check whether reinvestment in a sold position will trigger a wash-sale disallowance.

Missing the constructive receipt rule on deferred income. Cash-basis taxpayers who delay depositing received funds — or who decline to cash checks received before December 31 — remain taxable on those amounts in the year they were received or made unconditionally available. Deferral requires that the income genuinely not be available or received yet, not merely undeposited.

FAQs

What is the single most impactful year-end strategy for S-Corp business owners?

The highest-value combination is coordinating salary, QBI exposure, and retirement plan contributions together — because all three interact. Salary affects both FICA cost and the QBI W-2 wage limitation. Retirement contributions reduce taxable income and can shift clients below the Section 199A phase-out. Both must be locked in before December 31. Running these three optimizations independently, rather than together, consistently leaves money on the table.

Can a client contribute to a SEP-IRA after December 31 and deduct it for the prior year?

Yes. SEP-IRA employer contributions can be made up to the return's extended due date — October 15 for individual filers who requested an extension (IRS Publication 560). This flexibility is unlike 401(k) employee elective deferrals, which must be deposited before December 31. For clients who need post-year flexibility, a SEP-IRA is a structurally simpler option than a 401(k) for this reason.

What is the deadline to file Form 2553 for an S-Corp election effective January 1?

Form 2553 must be filed by March 15 of the tax year for which the election is to take effect. For new businesses, it must be filed within 75 days of formation. Late elections are available with IRS reasonable cause relief. Planning during Q4 of the prior year allows the election to be filed timely and effective on January 1, without relying on relief.

When is the latest a cash-basis business can defer invoicing to push income into the next year?

To defer income, the invoice must genuinely not be sent and the payment must not be received or constructively available before December 31. If payment is received via check or electronic transfer in December — even if undeposited — it is taxable in December under the constructive receipt doctrine (IRC §451 and Treas. Reg. §1.451-2). Deferral works when the income genuinely has not arisen yet, not when payment has already been tendered.

How does a year-end Roth conversion affect estimated tax payments?

A Roth conversion increases taxable income in the year of conversion. If the conversion is large enough, it may push total tax liability above the prior-year safe harbor threshold (110% of prior-year tax for clients with AGI above $150,000). Clients who complete large Roth conversions late in Q4 should consider whether additional estimated tax payments or W-2 withholding adjustments are needed to avoid underpayment penalties. Calculate the conversion's tax impact before the Q4 payment deadline.

Are there year-end strategies unique to clients entering retirement or winding down a business?

Yes. Clients in low-income years due to retirement, business closure, or sale should evaluate Roth conversions more aggressively than usual, accelerate any NOL carryforward utilization (income up to the NOL absorbs at minimal or zero additional tax), and consider timing asset liquidations to capture long-term capital gain rates before income rises. Equipment and other depreciable assets sold in a winding-down year may trigger depreciation recapture — coordinate timing with the depreciation election history.

Arvori helps CPAs run year-end planning across their entire client roster — tracking S-Corp salary reviews, retirement plan contribution limits, QBI phase-out exposure, and estimated tax reconciliation in one place. Learn more at arvori.app.

Year-End Tax Planning Checklist for CPAs: 10 Strategies to Execute Before December 31