The tax year ends once, and it ends completely. Deductions not incurred, elections not filed, and contributions not routed by December 31 are usually gone (a few retirement accounts excepted). Every November we run clients through this same sequence — ordered by impact and deadline pressure.
Business Moves (Highest Dollar Impact First)
Owners control more levers than anyone — but only while the calendar is open:
- Fix S corp reasonable compensation with a final payroll run — and use bonus withholding to cure estimated-tax shortfalls retroactively
- Open a Solo 401(k) by December 31 (contributions can follow later) — miss the setup date and the year is lost
- Accelerate equipment and vehicle purchases into service before year-end for Section 179/bonus
- Prepay deductible expenses under the 12-month rule; stock up on supplies
- Cash-basis timing: delay December invoices or accelerate collections — pick your bracket
- Execute Augusta Rule meetings and document family payroll before the ball drops
Investor Moves
Portfolios reward December discipline:
- Harvest capital losses against gains (mind the 30-day wash-sale rule); $3,000 of excess offsets ordinary income
- Harvest gains tax-free if you sit in the 0% bracket this year
- Max HSA contributions — the only triple-tax-free account
- Take RMDs (penalties are brutal) and consider QCDs for charitable giving at 70½+
- Bunch charitable deductions via donor-advised funds; donate appreciated stock, never cash
- Evaluate Roth conversions in low-income years — fill the low brackets deliberately
Real Estate Moves
Property strategies have placed-in-service and documentation deadlines:
- Place new rentals in service (advertised and ready) before December 31 to start depreciation and enable cost segregation
- Complete repairs now; capital improvements can wait — the deduct-vs-capitalize line is a December decision
- Verify STR average-stay math and material participation hours while you can still add hours
- Finalize REPS time logs — reconstruction in March fails audits
- Check passive-loss positions before selling winners; a planned disposition releases suspended losses
The Meta-Move: Run a Projection
Every item above matters only in the context of your actual numbers. A November projection reveals which bracket you are in, whether QBI phase-outs threaten, if safe harbors are met, and which moves flip from smart to counterproductive. That projection — plus a prioritized action list — is exactly what our year-end planning sessions deliver.
Book before Thanksgiving; December calendars (ours and vendors') fill fast, and some strategies need weeks of lead time.
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Explore the serviceFrequently Asked Questions
What's the single most missed year-end deadline?
Solo 401(k) establishment. Unlike IRAs and SEPs (which allow spring contributions), the Solo 401(k) must exist by December 31 to accept employee deferrals for the year — and it is usually the largest deduction a profitable owner can create.
Can I deduct expenses I put on a credit card in December but pay in January?
Yes — for cash-basis taxpayers, credit card charges are deductible when charged, not when the card is paid. A legitimate way to accelerate deductions without draining December cash.
Is it too late to lower this year's taxes in December?
No — December is the last window, not a closed one. Payroll corrections, purchases, harvesting, charitable bunching, and retirement setup all still work. What is too late is April.
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About the author
Samera Harvey, EA — Enrolled Agent & Founder
Samera Harvey is an IRS Enrolled Agent and the founder of Simply Smart Tax Advisors. She began her career in public accounting serving high-net-worth families, multi-state entities, and corporate tax structures — then built her own real estate investment companies, renovated and resold hundreds of properties, and educated more than 2,000 aspiring investors. She founded Simply Smart Tax Advisors to help entrepreneurs build tax strategy alongside wealth, not after it.
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