August is when corporate year-end tax planning conversations start. Not December. By the time a CPA reaches out to a C corporation client in November, most of the actionable levers have already been pulled (or missed). The Q3 window is where the real work happens: reviewing estimated payments, evaluating compensation timing, and lining up capital expenditure decisions before year-end closes the books.
Estimated Tax Payments: The Math That Catches People
Corporations expecting to owe $500 or more in federal income tax for the year make quarterly estimated payments. The schedule for calendar-year corporations: April 15, June 15, September 15, and December 15. By August, two payments are already in the books and the third is six weeks out.
The safe harbor is 100% of the prior year’s tax liability, paid in four equal installments. For large corporations (those with taxable income of $1 million or more in any of the three preceding years), the prior-year safe harbor only applies to the first installment. After that, payments follow current-year projected tax. Underpayment penalties for 2026 accrue at 7% annually, compounded daily per quarter (IRS Form 2220).
Q3 is the last clean window to adjust. If the corporation’s income is tracking higher than projected, the September 15 installment is where the correction happens. Waiting until December narrows the margin and increases penalty exposure for the third quarter shortfall.
Shareholder Compensation: Getting the Balance Right
C corporation compensation planning runs in the opposite direction from S corps. With pass-through entities, practitioners typically minimize salaries to reduce payroll tax. With C corps, the corporation deducts salaries at the entity level, so higher compensation directly reduces the 21% corporate tax. The tension is between maximizing the deduction and staying within what the IRS considers reasonable for the services performed.
Bonuses accelerate deductions when timed correctly. An accrual-basis C corporation can deduct a bonus in the current year if the bonus is fixed by year-end and paid within 2.5 months of the close of the tax year (by March 15 for calendar-year corporations). That’s a planning lever with a very specific deadline attached to it.
Stock compensation adds another dimension. Incentive stock options (ISOs) and non-qualified stock options (NQSOs) create different tax consequences for both the corporation and the shareholder. NQSOs generate a corporate deduction at exercise equal to the spread between the exercise price and fair market value. ISOs don’t. Restricted stock elections under Section 83(b), which allow the recipient to accelerate income recognition to the grant date, also affect the timing of the corporate deduction. Year-end is the natural checkpoint for reviewing outstanding equity grants and their tax implications.
Income and Deduction Timing
For accrual-basis corporations, income recognition follows the all events test: income is recognized when the right to receive it is established and the amount is determinable with reasonable accuracy. Deductions require economic performance on top of meeting the all events test. Those timing rules create Q3 and Q4 planning opportunities that cash-basis practitioners don’t encounter in the same way.
Accelerating deductions into the current year (prepaying deductible expenses, timing inventory purchases, front-loading repairs) or deferring income recognition where the all events test hasn’t been fully satisfied are standard plays. But the corporate context adds wrinkles. Charitable contributions hit the 10% of taxable income ceiling. Contingent liabilities don’t satisfy economic performance until the contingency resolves. And related-party transactions face additional scrutiny on both timing and amounts.
Retirement Plan Contributions and Deadlines
C corporations have access to the full range of qualified retirement plans: 401(k) plans, defined benefit plans, profit-sharing plans, and (for owner-only businesses) solo 401(k) plans. The corporation deducts employer contributions, generally up to 25% of covered compensation.
For 2026, the total annual additions limit under Section 415(c) is $72,000 per participant (plus $8,000 in catch-up contributions for participants age 50 and older). The compensation limit for contribution calculations is $360,000. Employer contributions generate a deduction when funded by the tax return filing deadline, including extensions. For calendar-year C corporations, that’s April 15, 2027, or October 15, 2027, with an extension (IRS Publication 560).
The Q3 planning conversation is about whether the current contribution level captures the full available deduction. Increasing employer contributions reduces corporate taxable income dollar for dollar. For closely held corporations where the shareholders are also the employees, the interplay between salary, bonus, and retirement contributions drives the total tax picture across both the entity and individual returns.
Capital Expenditures: The Depreciation Window
The OBBBA restored 100% bonus depreciation for qualified property placed in service after January 19, 2025. Section 179 expensing increased to $2.5 million with a $4 million investment limit. For corporate clients considering equipment purchases, vehicle acquisitions, or other capital investments, the Q3/Q4 window is when the placed-in-service clock starts ticking.
“Placed in service” is the operative phrase. The asset doesn’t generate a depreciation deduction until it’s available and ready for use in the taxpayer’s trade or business. Ordering equipment in November that doesn’t arrive until January produces a 2027 deduction, not a 2026 one. That timing distinction makes August and September the last comfortable window for assets with meaningful lead times.
Surgent CPE’s Understanding Corporate Taxation: Formation and Shareholder Compensation (CTF2) with Dave Peters covers reasonable compensation standards, stock option mechanics, Section 83(b) elections, and the interaction between compensation planning and corporate tax liability. Available August 26, 2026. Details at surgentcpe.com/cpe-courses/CTF2.