By the time a corporate or personal tax return is being filed, most of the decisions that could have reduced the bill are already locked in. Tax planning is really a year-round exercise with one hard deadline: your fiscal year-end (or December 31 for most personal tax purposes). What you do before that date matters far more than anything after it.
What's worth reviewing before year-end
A few areas tend to move the needle most for owner-managed businesses: the split between salary and dividends for the year, the timing of any major equipment or asset purchases, whether there's room to make use of RRSP or TFSA contributions, and whether any income or expenses can reasonably be shifted across the year-end line without distorting the picture.
For incorporated businesses, there's also the question of how much to leave in the corporation versus pay out — a decision that depends on your personal cash needs, your corporation's investment plans, and where you sit relative to various tax rate thresholds for the year.
Why the timing matters
None of this is complicated in principle, but it only works if it happens with enough runway to act — ideally a real conversation in the fall, not a scramble in the final week of December. A short year-end check-in, even a 20-minute one, is usually enough to catch the handful of decisions that are still open and close out the ones that aren't.