Most of what your April tax bill will be is already decided by things that happen — or don't — before midnight on December 31. Here are five moves worth a serious look every fall.
1. Max out (or at least raise) retirement contributions
Money into a traditional 401(k) or similar workplace plan reduces this year's taxable income dollar-for-dollar, and December is your last chance to raise payroll deferrals for the year. Self-employed? A Solo 401(k) or SEP-IRA can shelter a substantial share of your profit — and some of those contributions can even be made after year-end, but the account setup often can't wait. Contribution limits adjust annually, so confirm your exact ceiling before you write the check.
2. Check your withholding while it can still be fixed
A W-4 that's been wrong all year can still be partially rescued in November and December, because withholding is treated as if it were spread evenly across the year no matter when it happens. A few extra-large withholdings from year-end paychecks can erase an underpayment penalty that quarterly catch-up payments can't. This is one of the highest-leverage, least-known year-end fixes.
3. Harvest investment losses — carefully
Selling losing positions in a taxable brokerage account lets those losses offset your capital gains, plus up to $3,000 of ordinary income, with the rest carried forward. The trap is the wash-sale rule: buy the same (or substantially identical) investment within 30 days before or after the sale and the loss is disallowed. Harvest deliberately, not in a December 30 panic.
4. Bunch your deductions
If your itemized deductions hover near the standard deduction, alternating years can beat splitting the difference: concentrate charitable gifts, elective medical procedures, and (where allowed) property-tax timing into one year to itemize big, then take the standard deduction the next. A donor-advised fund lets you take the full charitable deduction this year while distributing to charities on your own schedule.
5. Time business income and purchases
Cash-basis business owners have real control in December: equipment placed in service by year-end can often be deducted immediately, expenses paid now land on this year's return, and invoicing in January pushes income into next year. But timing only helps if it points the right way — in a low-income year, accelerating income into today's low bracket can be the smarter play. This is exactly the conversation to have before the year closes, not after.
The common thread
Every one of these moves expires at midnight, December 31. That's why we do year-end planning sessions with clients each fall — modeling the actual numbers, not guessing. If you want that look at your own year, the door's open.