Year-End Tax Checklist for CPA Firms: 12 Essential Client Items

November is the last month where your firm can actually change a client's tax bill. December 31 closes the window on estimated payments, retirement contributions, loss harvesting, required minimum distributions, and charitable deductions. The year-end tax checklist for CPA firms that send clients a clear action list in late October or early November captures that window. The firms that wait until December find their clients have already missed it. At BusAcTa Advisors, we've worked with hundreds of CPA practices on tax season preparation, and the firms that run the smoothest filing seasons share one habit: they send a structured client checklist in November, every year, without fail.

This guide is the framework for that checklist. Each item covers what the client needs to know, why the December 31 deadline matters, and what to flag to your office before year-end. The amounts below reflect tax year 2025 rules. Some thresholds change annually, so verify figures against the current-year IRS sources before sending.

This is general information, not tax advice. Clients should consult their tax professional about their specific situation before acting on any of these items.

Item 1: Confirm Q4 Estimated Tax Payments Are on Track

The fourth-quarter estimated tax payment covers income earned October through December. For most individual clients, it's due January 15, 2026. Missing or underpaying Q4 is the error that generates penalty notices in spring, long after your client thought filing season was over.

Ask your clients now: are they on track with their 2025 estimated payments? If their income rose this year due to a business sale, a large capital gain, or a banner year in their S-corp, their prior-year safe harbor may not cover the full liability. Walk them through the two safe harbors: 90% of the current year's tax, or 100% of last year's tax (110% if their 2024 adjusted gross income exceeded $150,000). If neither applies, they owe a penalty regardless of when they pay the balance.

Clients often miss the Q4 payment because it falls after the holidays. Put the January 15 due date in the checklist in bold. That single reminder prevents a disproportionate number of underpayment penalty notices. The IRS safe harbor rules are covered in detail on the IRS estimated taxes page.

Item 2: Maximize Retirement Account Contributions Before Deadlines Differ

Not all retirement account deadlines are December 31. Clients who don't know this miss opportunities or move money unnecessarily fast. What happens to a self-employed client who misses the December 31 solo 401(k) election window? They lose the ability to defer employee contributions for the year entirely. Here's what your checklist should cover for tax year 2025:

• 401(k) employee deferrals: Must be contributed through payroll by December 31. The 2025 limit is $23,500. Clients 50 and older can add a $7,500 catch-up for a total of $31,000. Clients who are 60, 61, 62, or 63 qualify for a SECURE 2.0 super catch-up of $11,250 instead of $7,500, bringing their total to $34,750. If a client hasn't maxed their 401(k) and payroll runs through December 31, this is the nudge they need.

• Traditional and Roth IRA: The 2025 contribution deadline extends to April 15, 2026. The limit is $7,000, plus $1,000 catch-up for those 50 and older. No rush, but clients should know it can still be done during filing season.

• SEP-IRA and solo 401(k): Employer contributions to SEP-IRAs can be made by the return due date including extensions. Solo 401(k) employee deferrals, however, must be elected by December 31 for many plan documents, even if the dollar amount is contributed later. This distinction trips up self-employed clients every year.

Solo 401(k) employee deferrals must be elected by December 31 even if the money doesn't move until filing season. Most self-employed clients don't know this until they miss it.

Item 3: Required Minimum Distributions Must Be Taken by December 31

This item has the highest penalty for missing it. Required minimum distributions from traditional IRAs, 401(k)s, and most inherited IRAs must be taken by December 31 for clients who reached age 73 under SECURE 2.0. A first-year RMD can be deferred to April 1 of the following year, but doing so means taking two RMDs in one tax year, which has income stacking consequences worth flagging.

The penalty for missing an RMD dropped under SECURE 2.0 from 50% to 25% of the shortfall, and further drops to 10% if the client corrects the failure within two years. That's still a steep cost. Your checklist should ask clients to confirm they've taken their full RMD for the year and check whether the amount matches what was calculated at the start of the year. Life events like account transfers, new beneficiary designations, or a change in marital status can shift the calculation.

For clients over 70½, remind them about qualified charitable distributions (QCDs). A QCD allows up to $108,000 in 2025 to flow directly from an IRA to a qualified charity and count toward the RMD, with zero income recognition. Clients who give to charity and take RMDs benefit significantly from this. The distribution must go directly from the IRA custodian to the charity before December 31, not through the client's bank account.

The QCD limit for 2025 is $108,000. Clients over 70½ who donate to charity can satisfy their RMD with a direct IRA-to-charity transfer and pay no income tax on that amount.

Item 4: Capital Gains and Loss Harvesting Must Settle by December 31

Is your client sitting on unrealized losses in their brokerage account? Tax-loss harvesting closes the 2025 window on December 31. A client who sells a losing position on December 31 and it settles that day has captured the loss. A client who sells on December 31 but settles on January 2 has a 2026 loss, not a 2025 one. Confirm with clients that trades need to settle before year-end, not just be placed before year-end.

Three rules to cover in your client communication:

• Wash-sale rule: A client who sells a position at a loss and buys the same or substantially identical security within 30 days before or after the sale loses the deduction. The 30-day window runs in both directions. If a client plans to repurchase, they need to wait 31 days or buy a different fund in the same sector.

• Net loss cap: Capital losses offset capital gains dollar for dollar. If losses exceed gains, the excess deducts against ordinary income up to $3,000 per year. Remaining losses carry forward indefinitely.

• 0% capital gains bracket: Clients with taxable income below $96,700 for married filing jointly (or $48,350 for single filers) in 2025 pay 0% federal rate on long-term capital gains. If your client's income lands in that range, ask whether realizing their gains intentionally this year makes sense before their income rises in a future year.

Item 5: Cash-Basis Business Owners Can Shift Income and Deductions

Cash-method businesses have real flexibility at year-end that accrual-basis clients don't. Your business-owner clients should review two moves before December 31.

First, accelerate deductible expenses. Paying a January vendor invoice in December, prepaying a business subscription, or purchasing needed equipment before year-end shifts that deduction into 2025. The OBBBA restored 100% bonus depreciation for 2025 assets. A client who buys a qualifying piece of equipment before December 31 can deduct the full cost in 2025. The Section 179 expensing limit for 2025 is $2,500,000, with a phase-out beginning at $4,000,000 of qualifying property placed in service during the year. That's a substantial planning opportunity for clients with equipment needs they've been deferring.

Second, defer income. A cash-basis business owner who delays sending a December invoice until January pushes that income into 2026. If the client expects a lower tax rate next year, or if they've had an unusually high 2025 income, deferring a few invoices by a week or two can have real tax value.

Item 6: S-Corp Owners Must Run Reasonable Compensation Through Payroll by December 31

S-corporation owners who take distributions but inadequate salary create two problems: IRS reasonable compensation risk and payroll tax exposure. If your S-corp clients haven't run sufficient W-2 wages through 2025 payroll, December is their last chance. A year-end payroll run can correct this, but it must process before December 31 to count for the 2025 tax year.

Year-end payroll is also the window to confirm FSA elections, reconcile payroll records to year-to-date payroll tax deposits, and make sure the Q4 941 will match W-2 totals. Mismatches between 941s and W-3 totals generate IRS notices and can delay processing of the year's employment tax filings. Your checklist should ask clients to confirm they've reviewed their 2025 payroll summary before the last pay run of the year.

Item 7: Charitable Contributions Need Proper Documentation Before Year-End

A client who gives to charity on December 31 with the right documentation deducts it in 2025. Your client who gives without documentation can't deduct it at all. The rules differ by contribution type:

• Cash contributions: A bank record or written acknowledgment from the charity for any amount. No cancelled check means no deduction.

• Non-cash contributions over $250: A written contemporaneous acknowledgment from the charity, stating what was given and whether any goods or services were received in exchange.

• Non-cash contributions over $500: Form 8283, Section A, required. Over $5,000 requires a qualified appraisal.

• Donor-advised fund (DAF) contributions: The deduction is taken in the year the contribution is made to the DAF, not when grants are distributed to charities. A client who funds a DAF by December 31, 2025 can deduct the full contribution in 2025 even if they don't direct grants until 2026 or later.

For your clients who itemize, bunching two years of charitable contributions into one year can push them over the standard deduction in alternating years. If your client's charitable giving is close to the standard deduction threshold, December is the right time to model whether bunching in 2025 makes sense.

Item 8: HSA Contributions Can Still Be Made Through Tax Filing Day

Health savings account contributions for 2025 can be made through April 15, 2026, not just December 31. That makes this item different from most items on this checklist, but it still belongs in the November communication.

Why? Because clients need to confirm they were enrolled in a qualifying high-deductible health plan for 2025, and that their 2025 coverage won't have gaps that reduce the contribution limit. The 2025 limits are $4,300 for self-only HDHP coverage and $8,550 for family coverage. Clients aged 55 or older can add a $1,000 catch-up contribution. These are among the best dollar-for-dollar tax deductions available: contributions reduce taxable income, growth is tax-free, and withdrawals for qualifying medical expenses are also tax-free. Clients who haven't maxed their HSA by December 31 still have months to act, but they need to confirm eligibility now.

Item 9: Annual Gift Tax Exclusion Does Not Carry Forward

The 2025 annual gift tax exclusion is $19,000 per donor per recipient. Unused exclusion does not carry forward to 2026. A client who wants to give $19,000 to each of three children must do so by December 31 or lose the 2025 exclusion for those gifts permanently.

Married couples can combine exclusions for $38,000 per recipient per year through gift splitting, provided both spouses file Form 709 consenting to the arrangement. The IRS confirmed the annual exclusion holds at $19,000 for both 2025 and 2026. For clients with significant wealth transfer goals, December is the action window. Clients who want to superfund a 529 plan can contribute up to five years of exclusions in a single year ($95,000 per donor, $190,000 for a married couple) and elect to spread the gift tax reporting over five years.

Item 10: Start Collecting Year-End Documents in January, Not March

Your clients who create the least friction during filing season are the ones who start gathering documents in January. Your November checklist should tell clients exactly what to watch for when the mail and email arrive in January and February:

• W-2s from employers (due to employees by January 31)

• 1099-INT and 1099-DIV from banks and brokerages (due by January 31 or February 15)

• 1099-B and year-end brokerage statements showing cost basis and proceeds

• 1099-R for any retirement distributions taken in 2025

• K-1s from your clients' partnerships, S-corps, and trusts (often delayed until March)

• Form 1098 for mortgage interest paid

• Property tax statements

• Charitable contribution receipts and acknowledgment letters

• Business mileage logs and home office records

• Health insurance Form 1095-A for clients who purchased coverage through a marketplace

The K-1 timing is worth flagging specifically. Partnerships and S-corps don't have to issue K-1s until March 15. Your clients who expect K-1 income should know they may need to file an extension and shouldn't assume they can complete their return before K-1s arrive.

Item 11: Review QBI Deduction Position and Section 199A Wage Limitations

The qualified business income deduction under Section 199A allows eligible taxpayers to deduct up to 20% of their qualified business income from a pass-through entity. The deduction was made permanent under OBBBA. However, for your clients whose 2025 taxable income exceeds $383,900 for married filing jointly (or $191,950 for single filers), the deduction starts to phase out and W-2 wage limitations kick in.

For clients in the phase-out range, the deduction is capped at the greater of 50% of W-2 wages paid by the business, or 25% of W-2 wages plus 2.5% of the unadjusted basis of qualifying depreciable property. If your S-corp client is in the phase-out range, a year-end payroll run that increases their W-2 wages can increase their QBI deduction. That's the kind of year-end analysis that pays for itself many times over in your clients' tax savings. Review this with any business-owner whose income is approaching their threshold.

Item 12: Energy Credits Have Per-Year Limits That Reset January 1

The Energy Efficient Home Improvement Credit under Section 25C was made permanent by OBBBA. The annual cap is $1,200 for most improvements (insulation, windows, doors, HVAC), with a separate $2,000 annual limit for heat pumps and biomass stoves. These limits reset every year. A client who didn't use this credit in 2025 can't carry it back. If your clients are planning home energy improvements, ask whether they could make their qualifying purchases before December 31 to capture their 2025 credit.

The Residential Clean Energy Credit (solar panels, battery storage, fuel cells) still has no annual dollar cap and remains at 30% for systems placed in service in 2025. Unlike the 25C credit, this one carries forward if the taxpayer has insufficient tax liability. But a client who installs a system in December still needs it placed in service and operational before year-end to qualify for 2025.

Send the Checklist in November, Not December

The year-end tax checklist for CPA firms works only when it reaches clients early enough to act. A checklist that arrives in mid-December gives clients two weeks. The same checklist in early November gives them six. The clients who miss year-end deadlines are usually the ones who didn't know they were coming, and the ones who miss them usually blame their CPA, not themselves.

Sending this checklist is also a practice development tool. It signals expertise, it shows you're thinking about clients before they're forced to call, and it creates natural conversations about planning work your firm can provide. If your team doesn't have capacity to prepare and send individual client summaries, reach out to BusAcTa Advisors to explore how our offshore tax preparation team frees your domestic staff from production work so they can spend November on client communication rather than data entry. You can also learn how our tax planning and advisory support can extend what your firm delivers to clients without adding headcount.