One Big Beautiful Bill + Year-End Tax Deadlines: What CPA Firms Should Know Before Year’s End

Published December 4, 2025

Why This Year-End Is Different Under the One Big Beautiful Bill

The One Big Beautiful Bill Act (Public Law 119-21) was signed on July 4, 2025 and reshaped a wide swath of the federal tax code. The law’s scope is outlined on Congress.gov’s bill page for H.R. 1 and in overviews like PwC’s summary of the One Big Beautiful Bill Act.

For CPA and EA firms, three themes matter most at year-end:

• New “no tax on tips,” “no tax on overtime,” and “no tax on car loan interest” provisions for qualifying workers and vehicles, detailed in the IRS fact sheet “One, Big, Beautiful Bill Act: Tax deductions for working Americans and seniors”.
• A reinstated and expanded ability to deduct car-loan interest and other items, highlighted in IRS guidance on updating withholding for 2025 tax law changes.
• Permanent and extended business expensing rules that make the placed-in-service date for 2025 capital investments especially important, discussed in Tax Foundation’s “One Big Beautiful Bill: Pros & Cons”.

What your clients do before December 31, 2025 will determine how much they actually benefit on their 2025 returns.

December 15, 2025 – Fourth Estimated Tax Payment for Calendar-Year C Corporations

For calendar-year C corporations, the fourth 2025 estimated tax payment is due December 15, 2025. The corporate estimate schedule is laid out in IRS Publication 509 – Tax Calendars.

Under the One Big Beautiful Bill, corporate taxable income for 2025 may be very different from what you projected earlier in the year, particularly if clients:

• Qualify for new deductions or exclusions tied to compensation and financing.
• Have accelerated or expanded capital investments in 2025.

Year-end actions for CPAs and EAs:

• Re-forecast each corporate client’s 2025 taxable income using updated assumptions under the new law.
• Recalculate the Q4 estimate to reflect new deductions and any major 2025 transactions.
• Confirm the December 15 payment is correctly scheduled in EFTPS and documented in your workpapers.

By December 31, 2025 – Required Minimum Distributions (RMDs)

Clients already subject to Required Minimum Distributions must generally take their 2025 RMD by December 31 to avoid excise tax. The basic rules and penalty structure are summarized in the IRS “Retirement Plan and IRA Required Minimum Distributions FAQs”.

From a firm perspective, RMDs are low-hanging fruit for proactive risk management:

• Generate an RMD list from your tax or planning software.
• Confirm which clients have not yet satisfied their 2025 RMD.
• Verify with custodians that distributions have been processed, not just requested, before year-end.

A short RMD review can prevent one of the most avoidable (and painful) individual tax penalties.

By December 31, 2025 – Charitable Contributions That Count for 2025

To be deductible on a 2025 individual return, charitable contributions typically must be completed by December 31, 2025.

The One Big Beautiful Bill also sets up new charitable deduction rules for 2026 and beyond, including changes to AGI limits and a universal deduction structure discussed in year-end planning pieces like Kiplinger’s “How to Maximize Your Generosity Before the 2026 Cap Kicks In”.

That makes 2025 a pivotal year to revisit charitable strategy:

• Identify charitably inclined and higher-income clients.
• Decide whether it makes sense to “bunch” multiple years of giving into 2025 while current rules still apply.
• Coordinate with donor-advised funds and charities to ensure transfers are fully received by 12/31.

By December 31, 2025 – Capital Investments and Placed-in-Service Timing

The One Big Beautiful Bill permanently extends generous expensing rules for certain business property. Analyses like Tax Foundation’s overview of the One Big Beautiful Bill and tax-industry coverage note that the placed-in-service date for qualifying property remains critical.

For your business clients, the key questions are:

• What equipment, technology, vehicles, or improvements did they plan to acquire in 2025?
• Which of those assets will actually be installed and ready for use by December 31, 2025?
• Does expensing a purchase in 2025 vs. 2026 create a better overall result once federal, state, and cash-flow implications are considered?

The answer will differ by client, but the conversation must happen before year-end if you want the option to treat 2025 as the “expensing year.”

Other OBBB-Driven Year-End Conversations

Even where there is no formal filing deadline, the One Big Beautiful Bill creates planning windows that effectively close on December 31, 2025:

• Compensation structure – The IRS highlights new deductions related to tips, overtime, and car-loan interest in its One, Big, Beautiful Bill fact sheet. Payroll records and year-end reconciliations should support whatever treatment your clients plan to claim.
• Retirement plan deferrals – Articles like Kiplinger’s “21 Money Moves Smart People Are Making Before 2026” encourage maximizing salary deferrals and catch-up contributions before year-end, especially now that brackets and credits interact with the new law.

A simple way to frame it for clients:

“Because of the One Big Beautiful Bill, December 31 isn’t just the end of the year – it’s the last day to lock in many of the best 2025 tax outcomes.”

A Focused Year-End Checklist for CPA and EA Firms

To keep your internal process manageable, a practical thought-leadership checklist for 2025 might look like this:

• Re-run Q4 corporate estimates for calendar-year C corporations before December 15.
• Confirm all RMDs for 2025 are taken and documented by December 31.
• Review charitable giving timing with priority individual clients.
• Verify which capital assets will be placed in service in 2025 and how they will be treated.
• Align payroll and planning conversations with how tips, overtime, and related items will be reported under the new law.

Handled thoughtfully, this year-end is a chance for CPAs and EAs to show clear judgment in the first full year of the One Big Beautiful Bill – turning a complex law into concrete, time-bound actions that protect and advance client outcomes.