By the time a return is prepared, most of the meaningful decisions have already been made — how much was contributed, when a property was sold, which entity held the asset, and in which state the income was earned. Q4 is the last window in which those choices are still open.
Start with income timing. If this year is unusually strong, deferring revenue or accelerating deductions may help; if next year looks stronger, the opposite may be true. What matters is that the choice is deliberate and documented.
Next, look at retirement and entity contributions. Owner contributions, defined benefit plans, and health coverage decisions all carry deadlines that arrive quietly in the final weeks of the year.
Finally, confirm your estimates. A safe harbor miss produces an underpayment penalty that no amount of good planning erases after the fact. Review the year to date, not the year you planned for in January.