Most year-end tax problems are not knowledge problems. They are timing problems. The owner knew the move existed, just found out about it on December 28, when it was already too late to execute. A good small business CPA runs this list in late summer for exactly that reason. Here is the version you can run yourself.

Work through these before Q4 actually starts:

  • Pull your real year-to-date profit. Everything below depends on knowing where you actually stand, not where you guessed in January. If the number moved, your estimated payments are probably wrong.
  • Recalculate your September 15 estimated payment. Q3 is due that day. Paying last quarter's figure again is how penalties or overpayments happen.
  • Check where you land against the QBI thresholds. For 2026 the full 20% deduction runs up to $201,750 taxable income for single filers and $403,500 for joint (Rev. Proc. 2025-32). If you are tracking near a line, compensation can be adjusted now, not after you cross it.
  • Revisit your entity structure at current profit. The setup that fit at day-one revenue may be leaking self-employment tax at today's numbers. An S-corp election takes time to do right, so August is the window, not December.
  • List the equipment or property you were going to buy anyway. Timing a purchase into the right tax year can shift a real deduction. This only works if you decide before the year closes.
  • Look at retirement plan options. Some plans have to be established before year-end to count. A SEP-IRA, solo 401(k), or defined-benefit plan can move meaningful income, but not if you start the paperwork in January.
  • Gather documentation for anything credit-related. R&D and innovation credits require records built during the work, not reconstructed at filing. If you did qualifying development this year, start the file now.
  • Confirm your extended returns are on track. If you filed an extension, the S-corp and partnership deadline is September 15 and the individual deadline is October 15. Do not let those collide with your holidays.
  • Book the planning conversation. Every item above works better with a second set of eyes while there is still runway.

The honest read on all of this: the difference between an owner who keeps more and one who overpays is rarely a secret strategy. It is usually just four months of runway versus four weeks. If your current CPA has not raised a single one of these with you yet, that silence is the finding.

HYON Q runs this checklist with clients from Chicago, Miami, and Houston before Q4 begins. Free 30-minute call: https://www.hyonq.com/book-consultation