Year-End Tax Planning: The Moves Worth Making Before December 31st

Every year I have the same conversation a dozen times in March. A client opens their books for the prior year, sees a tax bill bigger than expected, and asks the same question: What could I have done differently?

The honest answer is almost always something — and almost always something that would've had to happen before December 31st. Tax preparation in spring is reporting. Tax planning in fall is strategy. The two are not the same job.

This piece walks through the moves I revisit with clients every Q4. None of it is exotic. All of it is legal. And most of it can meaningfully change what you owe — but only if you act in time.

General guidance for educational purposes — not personalized advice. The right moves for your situation depend on your entity type, income level, state of operation, and a dozen other factors. Talk to a tax professional before acting on any of this.

Start with what you actually owe

Year-end planning starts with a real estimate of your tax position. Not a guess. Not last year's number. A current calculation based on the books through (at minimum) October — including a projection for November and December.

If your bookkeeping isn't current enough to produce that estimate, that's the first problem to solve. You can't plan around numbers you don't have. Most of my clients get a Q4 projection in late October so they have eight to ten weeks to act on it.

With a real number in hand, you can ask the actual planning question: am I trying to lower this year's tax bill, smooth income across years, build retirement savings, or fund growth? Different goals point to different levers.

The retirement contribution lever

For most self-employed owners and small business owners I work with, retirement contributions are the single biggest deduction lever available — and the one most often left underused.

The mechanics depend on your situation:

• SEP-IRA — funded entirely by the business, contribution limits scale with net self-employment income. Easy to set up, can be funded as late as the tax filing deadline (including extensions).
• Solo 401(k) — for owners with no employees other than a spouse. Generally allows higher contributions than a SEP at the same income level because of the employee deferral component.
• SIMPLE IRA — for businesses with employees, lower contribution ceilings but lower administrative burden than a 401(k).
• Defined benefit plans — for high earners with stable income, allow contributions well into six figures. Complex, expensive to administer, but powerful when they fit.

The right choice depends on your entity, your income, whether you have employees, and what you want this account to do over the next decade. The wrong choice locks you into administration costs that eat the benefit.

Income and expense timing

If you're on cash-basis accounting — which most small businesses and sole proprietors are — you can shift the timing of income and expenses across the December 31 line. This is one of the simplest levers and one of the most overused.

The principle: deductions are worth more in your highest-bracket year. Income is taxed less in your lowest-bracket year. So you accelerate or defer based on which year is going to be heavier.

Practical moves:

• Pay January's bills in late December if you want this year's deduction. Pay them in January if next year's projected income is higher.
• Hold off on December invoicing if you can — push that revenue into January so it's taxed next year.
• If you're on accrual basis, this lever does not work the same way. Income is recognized when earned, not when received. Talk to your preparer about what timing changes actually move the needle for accrual-basis businesses.

The trap is over-shifting. Pushing too much income into next year works only if next year is genuinely lower. If your business is growing and next year will be even bigger, you're often better off recognizing income now at a lower rate than deferring it into a higher one.

Section 179 and bonus depreciation

If you've been planning to buy equipment, vehicles, or technology, the timing matters. Section 179 lets you deduct the full cost of qualifying property in the year you place it in service, up to an annual limit. Bonus depreciation works alongside it for assets that exceed those limits.

Two things to know:

• Place in service means the asset is ready and available for its intended use — not just purchased. Buying a truck on December 28 and registering it on January 4 disqualifies it from this year's deduction.
• Bonus depreciation percentages have been phasing down. The amount you can deduct this year may be different than last year. Confirm current rules with your preparer before assuming.

This is also where I see owners overspend. Buying a $60,000 truck to "save on taxes" when you didn't need a truck is just spending $60,000 to save the tax on $60,000 — usually somewhere between 15% and 35% of the cost. The other 65% to 85% is just gone.

S-corp owners: review your reasonable compensation

If you operate as an S-corporation, the IRS expects owners who work in the business to take a "reasonable salary" via W-2 wages before taking the rest of profits as distributions. Year-end is the time to review whether your salary actually meets that standard.

Two failure modes I see often:

• Salary too low. The classic mistake. The IRS scrutinizes S-corps that take large distributions and minimal wages, and the consequences range from reclassification to penalties.
• Salary too high. The opposite mistake. Paying yourself more than the business profits supports just to "feel safe" gives up the entire tax-savings advantage of the S-corp election.

If your year ended differently than projected — bigger or smaller — you may need to true up your wage in December. Once January 1 hits, the year is closed and amendments get expensive.

The QBI deduction and how it changes the math

The Qualified Business Income deduction (Section 199A) lets many pass-through business owners deduct up to 20% of qualified income. It interacts with W-2 wages, asset basis, and income thresholds in ways that make Q4 a useful checkpoint.

At certain income levels, additional W-2 wages or capital investments inside the business can increase your QBI deduction. At other levels, the same moves do nothing. This is modeling work — your preparer should be able to show you how the numbers shift before you act.

Q4 estimated tax true-up

Most small business owners owe quarterly estimated payments. The fourth quarter payment (due January 15 of the following year) is the last chance to catch up if your earlier estimates fell short.

Underpayment penalties aren't catastrophic, but they're avoidable. A late-October projection should tell you whether your Q1–Q3 payments matched the year you actually had — and whether to increase the Q4 payment to clear the safe-harbor threshold.

Multi-state owners: don't forget the states

Federal planning gets most of the attention, but state-level decisions can be just as expensive — especially if you have nexus in more than one state. Each state has its own rates, brackets, deductions, and filing thresholds.

A few reminders for owners with multi-state operations:

• State conformity to federal tax law varies by state and changes year to year. A bonus depreciation deduction that flows to one state's return may not apply on another's.
• Pass-through entity (PTE) elections — available in many states — can sidestep the federal SALT cap for owners. Election deadlines and mechanics vary widely. Some are due before year-end; some can be made on the return.
• Apportionment changes if your sales mix shifts between states. December is when you confirm your apportionment factors are still accurate for the year you actually had.

Charitable giving — strategy, not afterthought

For owners who give to charity anyway, year-end is when timing and structure can multiply the value. A few approaches worth a conversation:

• Bunching — concentrating two or three years of giving into one year so the total exceeds the standard deduction threshold and the giving actually delivers a tax benefit.
• Donor-advised funds — make the deductible contribution this year, distribute to specific charities over time.
• Appreciated assets — donating appreciated stock instead of cash avoids the capital gains and still delivers the deduction.
• Qualified charitable distributions — for clients over 70½, IRA distributions sent directly to charity satisfy required minimum distributions without triggering taxable income.

A working December checklist

If you remember nothing else, run this in early December:

1. Books current through November, projection for December.
2. Estimated full-year federal and state tax position calculated.
3. Retirement contribution decision made — and account established if a new plan.
4. Section 179 / bonus depreciation purchases planned for "place in service" before December 31.
5. S-corp reasonable compensation reviewed and trued up if needed.
6. Q4 estimated tax payment calculated.
7. Multi-state filings and PTE elections identified.
8. Charitable giving timed and structured intentionally.
9. 1099 vendor list reviewed and W-9s collected for anyone you'll need to issue.
10. Calendar invite for early January: pull final reports, prep tax documents, hand off to preparer.

The longer view

Year-end planning isn't just about this year's bill. The clients I watch grow over decades treat tax planning as one ongoing conversation — entity structure, retirement strategy, succession, estate. Each year's decisions compound.

The owners who pay the most over a lifetime aren't the ones with the biggest businesses. They're the ones who treated taxes as a once-a-year emergency every year, instead of as the year-round discipline it actually rewards.

This article is general educational information, not tax advice. Tax law changes regularly and individual circumstances matter. For guidance on your situation, schedule a consultation.