Year-End Tax Planning: What’s Off the Table and What You Can Still Do Before December 31

By late Q4, some of your most powerful tax strategies have already expired. You can no longer set up a new SIMPLE IRA or 401(k) for this year, change your entity structure retroactively, or fix a whole year of missed estimated payments. Profit sharing may still be an option for some existing plans, but the window is closing fast.

Plenty of real, money-saving moves are still on the table before December 31. You can accelerate deductions, time income, buy qualifying equipment, max out contributions to plans you already have, and make strategic charitable gifts. The key is knowing which doors have closed so you can sprint through the ones still open.

If you run a business doing $1M or more in revenue, the last stretch of the year is not the time to freeze. It’s the time to act decisively on what remains. This post breaks down exactly what you’ve missed, what you can still capture, and the questions worth asking your advisor before the calendar turns.

Quick Reference: Off the Table vs. Still Available

Why Timing Decides Your Tax Bill

The difference between a smart tax year and an expensive one usually comes down to timing, not effort. Owners who overpay aren’t careless. They’re late. They wait until December to think about taxes, and by then the structural strategies that needed months to execute have quietly expired.

Some tax moves are like planting a tree. You can’t decide in December that you wish you’d planted it in March. But other moves are more like harvesting. If the fruit is on the branch, you can still pick it. Your job right now is to stop mourning the tree you didn’t plant and start filling your basket.

Key takeaway: You’ve likely lost some options for this year. That’s fine. Focus your energy on the ones you can still control before December 31.

What’s Off the Table

Let’s be candid about the strategies that have already closed for the current tax year. Knowing these matters for two reasons. First, it stops you from chasing dead ends. Second, it tells you exactly what to set up early for next year.

Setting Up a New SIMPLE IRA or 401(k)

A brand-new SIMPLE IRA generally must be established by October 1 to count for the current year. The deadline to set up a new 401(k) for this tax year has also passed. If you’re reading this in November or December without either plan already in place, those doors have closed. It’s a common miss, and it’s frustrating because the tax savings are real. Put both on your list for next year and set the deadlines in your calendar now so you don’t repeat the same miss.

Changing Your Entity Structure Mid-Year

You can’t wave a wand in December and retroactively become an S-corp for the full year. Entity elections and structural changes take planning and lead time, and the window to reshape how your income was taxed this year is effectively closed. What you can do is evaluate whether a different structure makes sense going forward, which we’ll cover in the next section.

Fixing a Full Year of Estimated Tax Payments

If you underpaid your estimated taxes across the first three quarters, you can’t rewrite that history. Underpayment penalties may already be baked in. You can soften the damage with your final Q4 payment, but you can’t undo three quarters of missed deposits. This is why quarterly reviews matter so much.

New Retirement Plan Setup

If you were hoping to launch a new employer-sponsored retirement plan for this year, that opportunity has passed for both SIMPLE IRAs and 401(k)s. However, if you already have an existing plan that includes a profit-sharing feature, that option may still be within reach. But, the window is closing quickly. Contact your advisor now to confirm whether you’re still eligible and what it would take to act in time.

Key takeaway: If a strategy required setup earlier in the year, don’t burn hours trying to force it now. Document it as a first-quarter priority for next year and move on.

What You Can Still Do Before December 31

Now for the good news. A meaningful set of moves remains available right up to the last day of the year. Work through them deliberately, ideally with your advisor.

Accelerate Deductible Expenses

If you expect a strong tax year, pulling forward expenses you’d otherwise pay in the first few months of next year can lower this year’s taxable income. Think software renewals, supplies, professional services, or maintenance you already planned to buy. A good rule of thumb is if you’ll need it within the first six months of next year and can pay for it now, consider accelerating it.

Time Your Income With Intent

You have some control over when revenue lands. If deferring a few invoices into January makes sense for your position, that shift can move income into next year. If this year is unusually light, the reverse may serve you better. The point is to make the choice on purpose, based on your numbers and not by accident.

Buy Equipment and Use Section 179

Major purchases like equipment, vehicles, or technology can unlock a current-year deduction under Section 179, but the asset generally must be purchased and placed in service by December 31, not simply ordered. Don’t rush a bad decision just for the write-off. But if a purchase was already on your roadmap, timing it before year-end can be smart.

Max Out Contributions to Plans You Already Have

While you can’t create a new SIMPLE IRA or 401(k) at this stage, you can keep funding retirement plans already in place. Contributing more to an existing 401(k) or SEP IRA reduces taxable income while building long-term wealth. And if your existing plan includes a profit-sharing component, that window may still be open, but time is running out. Reach out to your advisor now to confirm eligibility and deadlines before that option disappears. Contribution limits and deadlines vary by plan type, so it’s worth a quick conversation to make sure you’re capturing everything still available to you.

Make Strategic Charitable Gifts

Cash donations to qualified charities made before December 31 can be deductible this year. Even better, gifting appreciated assets (like stock you’ve held) can help you avoid capital gains while still claiming a deduction. If giving is already part of your plan, timing and method matter as much as the amount.

Review Your Entity Structure for Next Year

You can’t change this year’s structure, but December is an ideal moment to ask whether your current setup still fits. Businesses evolve fast, and entity structures often lag behind. If you launched as an LLC and have since grown substantially, an S-corp election may be worth modeling for next year. Start that conversation now.

Book a Planning Session With Your CPA or CFO Advisor

This is the most overlooked move on the list, and often the most valuable. Many remaining strategies only work if you act before year-end, and you won’t know which apply to your situation unless you ask in time. A focused conversation now can surface opportunities you didn’t know existed.

Key takeaway: Several of these moves stack. Accelerating deductions, timing income, funding retirement, and giving strategically can work together, but only if you coordinate them before the deadline.

Who This Is For

This advice is written for founder-led businesses doing $1M or more in revenue, where the tax stakes are high enough that timing genuinely moves the needle. You’ll get the most from this if you recognize yourself below:

• You tend to think about taxes only when it’s time to file
• You haven’t had a real strategy conversation with an advisor this year
• You’re unsure which retirement or entity deadlines have already passed
• You want to keep more of what you earn and reinvest it in growth
• You’re ready to stop reacting to your tax bill and start shaping it

If two or more of these describe you, the next few weeks are worth protecting.

What to Ask Your Advisor Before Year-End

Walking into a meeting with a stack of documents and no agenda turns a strategy session into a data dump. Bring these questions instead:

• Which deadlines are still open that would cost me money if I miss them?
• Based on where my income is landing, should I accelerate or defer anything?
• What equipment or purchases should I move into this tax year?
• How much more can I contribute to my existing retirement plan, and is profit sharing still on the table for us?
• Should I model an entity structure change for next year?
• What would you do differently if this were your business?

That last question tends to open the most useful part of the conversation. It invites your advisor to flag the things you didn’t think to ask about, which is usually where the real savings sit.

Frequently Asked Questions

Can I still set up a SEP IRA before the end of the year?

Yes. Unlike a SIMPLE IRA or 401(k), a SEP IRA can generally be established and funded up until your tax filing deadline, including extensions. This makes it one of the most flexible retirement options available to self-employed owners and small business operators.

What happens if I miss all the year-end tax deadlines?

Missing year-end deadlines doesn’t eliminate your options entirely. It just shifts your strategy to the following year. Use the remaining weeks to document what you’d do differently and set calendar reminders in January so you’re positioned to act early next year.

How do state taxes factor into year-end planning for business owners?

State tax rules often differ significantly from federal rules, including different deadlines, deduction limits, and entity treatment. Working with an outsourced CFO like us at Cobb CPA who understands your state’s specific requirements can help you avoid surprises and capture savings you might otherwise miss.

The Bottom Line: Act on What’s Still Open

Year-end tax planning isn’t about mourning the moves you missed. It’s about capturing every dollar still within reach before December 31. Some doors have closed like new SIMPLE IRAs, new 401(k) plans, mid-year entity changes, and a full year of estimated payments. If your existing plan includes a profit-sharing feature, that window may still be open, but it’s closing fast. Accelerating deductions, timing income, buying equipment, funding existing plans, and giving strategically are all still on the table for a business ready to act.

The owners who win at year-end are the ones who move fast on what remains and set up next year’s opportunities today. If you want a clear picture of exactly which strategies still apply to your business, don’t wait for the deadline to make the decision for you.

Ready to keep more of what you earned this year? Schedule a year-end tax planning consultation with our team before December 31 and give yourself the runway to actually act on what we find.

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Disclaimer: The information provided in this post is for general educational and informational purposes only. It does not constitute professional financial, tax, or legal advice. Because tax laws change and every individual’s financial situation is unique, you should consult with a certified public accountant (CPA) or a qualified financial professional before making any financial decisions or taking action based on this content.