Building a Stronger Tax Position Before Filing Season

The 2025 tax law changes raised the stakes on this window considerably. Several provisions now reward businesses that act before December 31 and quietly penalize those that wait. The difference between a Q4 decision and an April realization can run into six figures for a growing company, and none of it is recoverable once the year turns.

Bonus depreciation gives businesses an opportunity to accelerate deductions on qualifying investments rather than spreading them across several years. For property placed in service after January 19, 2025, 100% bonus depreciation allows businesses to deduct the full cost of qualifying assets in the year they are put to use. This can significantly affect the timing and tax impact of major capital purchases. Equipment, machinery, and qualified improvement property are among the assets that may qualify for immediate deductions.

The timing of the deduction is just as important as the amount. Assets placed in service before the January 19, 2025 threshold may receive different treatment, and businesses may have the option to elect a 40% rate instead of the full deduction in certain situations. Taking the largest deduction immediately is not always the best strategy, particularly if the business expects higher taxable income in future years. The right approach should account for projected income across multiple years, not just the current tax bill.

This is where cost segregation paired with bonus depreciation becomes worth a serious look before December 31. A cost segregation study breaks a building or major improvement into its parts, reclassifying elements that qualify for accelerated depreciation. Combined with 100% bonus depreciation, a study completed and applied this year can convert what would have been decades of slow deductions into a single large write-off. The purchase has to be timed correctly, and the property has to be in service, so this is a Q4 conversation, not an April one.

Section 179 gives businesses more control over how they deduct qualifying equipment and property. With a $2.5 million deduction limit and a phase-out beginning at $4 million in total purchases, businesses can choose how much to expense for individual assets rather than automatically applying the same treatment across every purchase.

That flexibility makes Section 179 a useful planning tool, especially when paired with bonus depreciation. A business can determine how much to deduct now based on its projected taxable income and preserve the remaining deductions for future years. The key is making those decisions while there is still time to evaluate where income is expected to land.

For example, a manufacturer purchasing a $600,000 production line has several options to consider. Depending on its income projections, it may make sense to expense the full purchase, combine Section 179 with bonus depreciation, or preserve some deductions for a future year. Modeling those options before making the election helps the business choose the approach that best supports its broader tax strategy.

Section 174A allows businesses to immediately deduct qualifying domestic research and development costs rather than spreading those deductions over five years. For companies investing in product development, software, engineering, or process improvements, this can create a more immediate tax benefit and improve cash flow. Eligible small businesses may also be able to apply the change to certain R&D expenses from prior years. That makes it worth reviewing previously capitalized costs to determine whether additional deductions are available. Documentation is an important part of capturing the benefit. Businesses need to clearly identify qualifying activities and connect them to the appropriate expenses. Reviewing those costs before filing can help uncover potential deductions and ensure the documentation is in place to support them.

The Qualified Business Income deduction, established under Section 199A, is now permanent, and a new $400 minimum deduction has been added for qualifying taxpayers. Permanence removes the planning uncertainty that came with a provision scheduled to expire, letting pass-through owners build multi-year strategies around a deduction they can count on. For owners of S corporations, partnerships, and sole proprietorships, the QBI deduction remains one of the more valuable provisions available, and its permanence makes it a fixture to plan around rather than a benefit to race against a sunset.

The planning around QBI is subtle because the deduction interacts with wage levels, business type, and taxable income thresholds. Owners who actively manage their W-2 wages and business structure can position themselves to capture more of the deduction, and those adjustments generally have to be made during the year rather than reconstructed after it closes. A well-timed compensation decision in Q4 can be the difference between capturing the full deduction and losing part of it to a threshold.

The state and local tax deduction cap rises to $40,000, a significant increase from the previous $10,000 limit that had constrained deductions for taxpayers in higher-tax states. For business owners who itemize and carry meaningful state income and property tax burdens, this expands a deduction that had been sharply limited for years. The increase changes the itemizing calculation for many owners and reopens planning around the timing of state tax payments before year-end. The higher cap makes the timing of deductible state and local payments worth revisiting in Q4. Prepaying certain state obligations, or timing them across tax years, can now capture more benefit than the old $10,000 ceiling allowed. Coordinating these payments with your overall income picture is the kind of move that only works while the year is open.

The safe harbor rules for estimated taxes set the thresholds you have to meet to avoid underpayment penalties, generally requiring payment of 90% of the current year’s liability or 100% of the prior year’s, rising to 110% for higher earners above $150,000 in adjusted gross income for married filing jointly, or $75,000 for single filers. Missing these thresholds triggers penalties that are entirely avoidable with attention before year-end. The safe harbor is a floor you either clear or you do not, and Q4 is the last chance to true up your payments before the clock runs out.

For a growing company, the danger is that a strong year pushes your actual liability well above what your quarterly payments anticipated. If your income has climbed faster than your estimates, a Q4 catch-up payment can bring you back inside the safe harbor and eliminate the penalty exposure. Waiting until you file means the underpayment is already locked in, along with the penalty that comes with it.

This is one of the more common places where growing companies leak money without realizing it. A single well-sized fourth-quarter estimated payment, calculated against a current income projection, often costs nothing beyond the tax already owed while erasing a penalty that would otherwise apply. It takes a real look at where the year has landed, which is a Q4 exercise by definition.

The provisions above share a common thread in that each one rewards a decision made while the year is still open and penalizes the same decision deferred to filing season. This is why proactive tax planning is an important part of financial planning, not simply a year-end tax exercise. A deduction not captured, an election not made, or a payment not timed becomes permanent the moment the year closes.

The math is stark for a profitable pass-through owner. The combined weight of federal income tax at rates reaching 37%, plus self-employment tax at 15.3%, means a high-earning owner can face well over 50 cents of tax on each additional dollar of income. Every dollar of deduction legitimately captured, and every dollar of income legitimately deferred or repositioned, is worth that full combined rate. At those levels, the difference between proactive Q4 planning and passive April filing is not a rounding error on a growing company’s return.

There is a human dimension to this problem that compounds the financial one. With CPA turnover running around 72%, the accountant who understood your business last year may not be the one preparing your return this year, and the institutional knowledge that made proactive planning possible often walks out the door with them. Continuity of tax insight has become something growing companies can no longer assume, which raises the value of a planning relationship built to persist rather than reset every filing season.

At KDG, we approach tax planning by helping businesses understand where their income is headed and identify the decisions that can still influence their tax position. From there, we evaluate opportunities such as bonus depreciation, Section 179, R&D expensing, QBI, SALT, and estimated tax payments based on the company’s actual financial picture. 

Our managed accounting and fractional CFO capabilities help maintain an accurate view of income throughout the year, while our tax planning expertise helps businesses evaluate how different strategies may affect both current and future tax obligations. Bringing those capabilities together allows planning decisions to be based on current financial data rather than estimates or a generic checklist. 

The goal is to enter filing season with fewer surprises and a clearer understanding of the decisions behind the tax position. It is part of treating tax readiness as an ongoing financial discipline and establishing a stronger provision-readiness process before filing begins.

Ready to plan?