The Year-End Tax Planning Checklist: Eight Moves With Real Deadlines

By late August, more of your tax year is locked in than most owners realize. The highest-impact moves left (S-Corp election timing for next year, retirement plan setup, equipment purchases, owner compensation changes) still have to happen before December 31 to count. Here's the eight-move checklist that turns the last four months into a planning window instead of a passive countdown.

Several of these deadlines say December 31 on paper. The lead time behind them runs out well before that, and that clock started already.

The Year-End Tax Planning Checklist at a Glance

The first deadline on this table comes fastest: the Q3 estimated payment, due September 15. Miss it, and it's the one move on this list you can't circle back to this year. Five more land on or at December 31: the retirement plan establishment window, the equipment purchase, the salary adjustment, the charitable contribution, and the entity filing. The remaining two run past year-end. The S-Corp election technically files in the following year, and HSA contributions aren't due until next April. Below is what each move requires and what missing it costs.

The Shape of the Remaining Four Months

Eight months of your tax year are already fixed. Income earned, expenses incurred, payments made — that part of 2026 is written.

What's left is four variable months. Every move on the table above needs a decision or action inside this window, even the two whose paperwork deadline technically lands later.

The cost of waiting until November isn't hypothetical. A defined-benefit plan needs six to eight weeks of actuarial work before it can be established. Start in November and you're not making the deadline — you're missing it. Equipment lead times work the same way. An order placed in late October is the last safe window for a December "placed in service" date, because placed in service means installed and running, not sitting in a warehouse.

"In tax, August is October. October is December. By the time most owners think 'year-end planning,' the year is already planned." — Mitchell Baldridge, CPA, CFP®, Visor Co-Founder

Late August through October gives you the most runway to execute all eight moves. Q4 can still work — it just works with less room for error. A quarterly review is where this list gets generated in the first place. These eight moves are what a Q3 review produces.

The Eight Moves

Move 1 — Recalibrate Q3 and Q4 Estimated Payments

Deadline: September 15

If your year-to-date income looks materially different from the projection that set your Q1 and Q2 payments, your Q3 payment needs to change with it. Pay at least 90% of your actual full-year tax liability across your estimated payments, or 100% of last year's tax (110% if your prior-year income topped $150,000). Either one satisfies the safe harbor. Miss both, and the IRS sets the Q3 2026 penalty rate at 7%, per Revenue Ruling 2026-10.

What it costs to skip. A $20,000 gap between your Q3 payment and what you owe, carried until you file next April, runs about $817 in penalty interest at the current 7% rate. That's not the tax itself. It's the cost of paying it seven months late instead of on September 15.

Move 2 — Set Up or Fund a Retirement Plan

Deadline: varies by plan type

A Solo 401(k) has to be established by December 31, though employer contributions can wait until your filing deadline. Providers need time to open the account and process the paperwork, so waiting until November cuts that margin close. A SEP-IRA is more forgiving. Open and fund it right up to your filing deadline, including extensions. A defined-benefit plan is the least forgiving of the three. It needs to be established by December 31, and the actuarial work behind it takes six to eight weeks, which is why October is the real deadline even though December 31 is the one on paper.

This belongs on the year-end list now, not in November, because the highest-leverage plans are also the ones with the least room for a late start. S-Corp salary determines how much you can put into these plans. The contribution limit is a function of W-2 wages, not net profit, which is one more reason reasonable-compensation planning and retirement planning aren't separate conversations.

Move 3 — Make the S-Corp Election for Next Year

Deadline: Form 2553, within 2.5 months of the tax year it applies to

August is when you should be running the math on next year's election, even though the filing itself happens early next year. If next year's projected profit clears the S-Corp breakeven, the sooner you start the process, the sooner the savings begin. There's no version of this where waiting until the deadline gets you a better outcome.

Run your own numbers against the S-Corp savings calculator before you decide. It uses your actual projected profit, not a rule of thumb. The breakeven point moves depending on your specific numbers.

Move 4 — Plan Major Equipment Purchases

Deadline: asset placed in service before December 31

The 2026 Section 179 deduction cap sits at $2,560,000, with the phase-out starting once total equipment placed in service crosses $4,090,000, and a separate $32,000 cap applies to SUVs, per IRS Publication 946 and Revenue Procedure 2025-32.

Those caps aren't the number that matters to you. At 400K–2M in profit, you're not buying $4 million in equipment — you're buying a $40,000 server upgrade or a $15,000 office build-out, and the full amount is deductible this year as long as it's in service by December 31. The phase-out exists for businesses buying at a scale you're nowhere near.

"Placed in service" is the phrase that trips people up. It means operational, not purchased. An invoice dated December 20 for a machine that isn't installed until January doesn't count for this year. At Visor, this conversation almost always starts the same way. An owner assumes the purchase date is what matters, learns it's the in-service date, and realizes they've cut their own runway by weeks without meaning to. Ordering in October is the safest window for a clean December delivery and installation.

Move 5 — Adjust S-Corp Reasonable Salary if Needed

Deadline: December 31

The adjustment has to hit payroll before year-end. If your income came in ahead of what you projected when you set your salary, the reasonable-compensation basis you used in January may no longer hold up. A $70,000 salary against $600,000 in profit is the kind of ratio that draws attention under the reasonable-compensation standard the IRS and courts apply, not because a formula flags it, but because it doesn't match what a comparable executive would earn doing that work in the open market.

A one-time year-end bonus run through payroll — not a 1099, not a distribution — is how you correct a salary that's fallen behind. Waiting until you file isn't an option. Payroll corrections have to happen in the calendar year they're correcting, which makes this one of the more time-sensitive items on the list despite the deadline sounding generous.

Move 6 — Maximize HSA Contributions

Deadline: April 15 of the following year

This is one of the few moves without a hard December 31 deadline. You can contribute for 2026 up until you file your 2026 return. The 2026 limits are $4,400 for self-only coverage and $8,750 for family coverage, plus a $1,000 catch-up if you're 55 or older, per IRS Publication 969.

It's also the move most likely to get skipped, because the deadline doesn't feel urgent in December. Set the reminder now, while you're already looking at the rest of this list, or it falls off your radar until it's too late to matter.

Move 7 — Time Charitable Contributions

Deadline: December 31 for a current-year deduction; substantiation required for gifts of $250 or more

Late August through October is the right window to map out the year's giving. This matters most if you're working with a donor-advised fund, gifting appreciated stock instead of cash, or making a qualified charitable distribution from an IRA at 70½ or older. Each has its own mechanics under IRS charitable contribution rules, and appreciated-asset gifts need enough lead time to transfer before December 31. That's not something you want to be coordinating with a brokerage on December 28.

If you're close to the standard-deduction threshold, bunching two years of giving into a single year through a donor-advised fund can push you back over into itemizing territory. That's a strategy decision, not a compliance one. That's why it belongs on a planning list instead of a last-minute one.

Move 8 — Review Entity and State Structure for Next Year

Deadline: filing in November or December for a January 1 effective date

A Q3 review is where this surfaces: a new business line that should sit in its own S-Corp, an entity you stopped using two years ago that's still costing you a filing fee and a K-1 every year, a state registration you need because you've built nexus somewhere you didn't intend to, or an ownership restructure tied to estate planning.

None of these are December decisions. They're August-through-October decisions that happen to take effect in December.

Executing the Year-End Tax Planning Checklist

A list of eight moves doesn't do anything by itself. What makes the difference is running quarterly tax planning as two structured reviews, not one vague intention to "get to it":

• A Q3 planning review in September or October that produces a written list of which moves apply to you, with an owner and a date attached to each one.
• A Q4 execution review in November or December that confirms what got done before the window closes.

Most owners who skip this don't skip it because the list is wrong. They skip it because "I'll get to it" doesn't have a deadline attached, and a defined-benefit plan setup does. The accountability of a scheduled review, not a New Year's resolution to be more organized, is the execution mechanism here.

Talk to our team if you want this list run against your actual numbers instead of the general version above.

Frequently Asked Questions

When should I start year-end tax planning for my small business?

Late August through October is the right window. By August, you have six-plus months of actual income to project against, enough runway to act on the major December 31 deadlines (Solo 401(k) setup, defined-benefit plans, equipment purchases, charitable timing) and enough time to file an S-Corp election for next year if the math supports it. Starting in November isn't too late for every move on this list; payroll adjustments, charitable timing, and funding decisions on existing plans still work. The higher-lift moves, like defined-benefit setup and entity changes for next year, need more runway than November provides.

What tax moves can I still make before December 31?

All eight moves on this checklist are available in August. Some get harder by September. A defined-benefit plan needs actuarial work that takes weeks to complete. By October, Solo 401(k) establishment is the last realistic window for a clean December 31 setup. By November, the list narrows to funding decisions on plans that already exist, payroll adjustments to S-Corp salary, equipment that can still ship and get installed before year-end, charitable timing, and HSA planning that carries into the following April anyway.

What's the difference between a Q4 tax review and a year-end scramble?

A Q4 tax review is a structured exchange between you and your CPA that ends with a written list of moves, each with an owner and a due date. A year-end scramble is what happens when that same conversation gets pushed to mid-December — too late for a defined-benefit plan, too late for a clean S-Corp election filing in Q1, often too late for equipment lead times. From the outside, both look like "talking to your accountant about taxes in the fourth quarter." The difference is whether the moves get executed or get rolled into next year's regret.

Do I need a CPA for year-end tax planning?

Most owners benefit from one. The simpler items (Q3 payment recalibration, charitable timing, basic Solo 401(k) funding) are manageable on your own. The higher-leverage moves (defined-benefit plan setup, multi-entity restructuring, S-Corp election timing, reasonable-salary recalibration) need professional judgment and a current-year projection most owners don't run themselves. A focused year-end planning conversation with a CPA who already knows your business is the highest-return hour you'll spend on taxes all year.

Want to run the eight-move checklist against your specific situation? Talk to our team, free.