Most year-end tax checklists are organized by topic: a section on retirement, a section on charitable giving, a section on capital gains, and so on. The problem with that organization is that it doesn't tell you what to do this week. By the time you finish reading the retirement section in late November, you've missed the window to set up some of the plans it describes.

Here is the same content, reorganized the way we actually run year-end planning with clients: by deadline. The earliest deadline is first. If a section's deadline has passed for your situation, skip it and act on the next one.

October: the strategic window

By October, you should have a reliable estimate of where the year is landing. The October moves are the highest-leverage, longest-lead-time items.

  • Run a year-end projection. Project your full-year taxable income, federal and state, with reasonable assumptions for the remaining months. The projection is the input to every other decision below. Without it, you're guessing.
  • Review reasonable compensation. If you're an S-Corp owner-employee, October is the last clean window to adjust W-2 wages for the year through normal payroll. Last-minute December bonus runs to "fix" reasonable comp work mechanically but invite scrutiny — gradual, steady payroll is more defensible.
  • Set up a defined benefit or cash balance plan. These plans typically must be adopted by year-end and require actuarial design that takes weeks. If you're the kind of high-earner candidate where these plans make sense (typically professional service firms and owner-physicians where contribution capacity well above standard 401(k) limits is meaningful), the conversation has to happen now, not in December.
  • Consider an entity restructuring. Late S-Corp elections under Rev. Proc. 2013-30 can be effective retroactively to the start of the current tax year if filed timely with reasonable cause. F reorganizations, partnership conversions, and similar restructurings all have lead times that compress poorly in December.
  • Schedule a cost segregation study. If you placed real estate in service this year (or in any open prior year), a cost segregation study reclassifies components into shorter-life depreciable categories and, when bonus depreciation under IRC §168(k) is in effect, accelerates substantial depreciation into the current year. The study itself takes 4–8 weeks; engaging the engineer in October produces a deliverable in time for year-end planning.
  • Identify capital gain or loss positions to harvest. Review concentrated positions, recently appreciated stock, RSU grants, or property holdings where the tax-aware sale or hold decision has been deferred. October pricing matters because December markets are noisy.

November: the action month

November is when most of the year-end work actually gets executed. The October-set plan converts into specific transactions.

  • Set up retirement plans that must exist by year-end. A Solo 401(k) for a self-employed individual generally must be established by December 31 to allow employee elective deferrals for the year. SEP-IRAs are more forgiving on setup deadlines (generally extending to the return due date) but the cleanest path is establishing the plan during the year, not after.
  • Fund elective deferrals through payroll. 401(k) elective deferrals are made through payroll and must be remitted from wages paid by December 31. If you wanted to defer the full elective limit and you've been under-deferring through the year, the December paychecks are your last chance.
  • Place equipment in service for §179 / bonus depreciation. "Placed in service" means installed and ready for its intended use by December 31 — not "ordered" or "paid for." Equipment ordered in late December that arrives in January is deductible next year, not this year.
  • Execute charitable giving strategies. Donor-advised funds, QCDs from IRAs (for those eligible), donations of appreciated stock, qualified charitable distribution timing — all need to be initiated with enough lead time for the receiving institution to process before year-end. Wires after Christmas often miss.
  • Time bonus payroll. Year-end bonuses paid before December 31 are deductible in the current year for cash-basis businesses. Timing larger bonuses around projected income matters when current-year and next-year tax brackets differ meaningfully.
  • Run a Roth conversion analysis. Conversions of traditional IRA balances to Roth must be completed (the funds actually moved) by December 31. The decision turns on this year's bracket vs. expected future brackets, available cash to pay the conversion tax, and whether you've already filled lower brackets.

December: the closing window

December is for completing what was planned, with a small set of December-specific items.

  • Pay state estimated taxes before year-end (when beneficial). For taxpayers itemizing and not subject to AMT, paying Q4 state estimated taxes in December rather than January generally accelerates the deduction by one year — but the SALT cap limits the benefit, and AMT can wipe it out entirely. Run the math; don't assume.
  • Make PTE election payments. If your state allows a Pass-Through Entity tax election to work around the SALT cap, the election typically requires payment by year-end (or by a specified date in the year) to be effective. Deadlines and mechanics vary materially by state.
  • Confirm payroll deferrals and contributions are processed. Verify that retirement deferrals and HSA contributions actually went through — payroll providers occasionally miss December items, especially around holiday processing schedules. A misfire isn't fixable after January 1.
  • Take required minimum distributions. If you're subject to RMDs from traditional IRAs or qualified plans, the year's RMD must be taken by December 31 (or April 1 of the following year for first-year RMDs, with planning consequences). The penalty for missing is severe.
  • Take S-Corp distributions to clear AAA. For S-Corps with prior C-Corp earnings and profits, the ordering rules can make ill-timed distributions tax-inefficient. December distributions to clear AAA before E&P kicks in can be the right call.
  • Document Augusta Rule rentals. If you're using the IRC §280A(g) Augusta Rule (the 14-day home-rental exclusion), the days, the rental rate, the documentation of fair market value, and the corporate minutes for the meetings held should all be finalized before year-end.
  • Loss-harvest if appropriate. Capital loss harvesting in December must navigate wash-sale rules (30 days before and after), so the December timing matters — and the market in late December tends to feature concentrated tax-loss selling that affects pricing.

January: the cleanup window

A few items are technically post-year-end but with deadlines that arrive quickly:

  • 1099 issuance to vendors. Form 1099-NEC for nonemployee compensation must be furnished to recipients and filed with the IRS by January 31. The data gathering — W-9s, vendor totals, addresses — is usually the bottleneck.
  • W-2 issuance. Same January 31 deadline. Make sure the 2% S-Corp shareholder health insurance premium has been added to the owner's W-2 in box 1 (and box 14) before the W-2 is finalized.
  • SEP-IRA and profit-sharing contributions. These can generally be made up to the return due date including extensions, but earlier funding gives the contributions more time invested.
  • HSA contributions for the prior year. Health Savings Account contributions for the prior year can be made up to the regular tax filing deadline (typically April 15).
  • IRA contributions. Same deadline — April 15 for the prior tax year.

What can’t be fixed after year-end

The point of starting in October is that several decisions are simply unavailable after December 31:

  • Adjusting reasonable compensation for the year (W-2 wages must be paid in the year).
  • Establishing a Solo 401(k) for elective deferrals (plan must exist by year-end).
  • Adopting a defined benefit or cash balance plan for the year (must be adopted by year-end, with limited exceptions).
  • Roth conversions for the year (must be completed by December 31).
  • Placing equipment in service for current-year §179 or bonus depreciation.
  • Capital loss harvesting (the sale must occur, and clear wash-sale rules, by year-end).
  • Most state PTE elections.
  • Augusta Rule rental documentation.

By contrast, several items can be addressed after year-end with proper extension management: SEP-IRA and profit-sharing contributions, HSA and IRA contributions, late S-Corp election relief in some cases, and tax-method changes via Form 3115. Knowing which is which determines what genuinely cannot wait.

The single biggest year-end planning mistake is treating December as the planning window. By December, most of the highest-leverage moves are already constrained or off the table. October is the planning window. December is the execution window.

How to use this checklist

For most owner-operated businesses, a working year-end process looks like this:

  1. By the second week of October, produce a year-end projection. (If you don't have one, building it is the first action.)
  2. Identify the items above that apply to your situation. Most businesses have between five and twelve items that genuinely apply — not all forty.
  3. Assign each item a deadline-driven owner: who is doing it, by when. Calendar the deadline.
  4. Execute through November and December, checking off items as completed.
  5. In January, run a quick close on the year's planning: what got done, what didn't, what to start earlier next year.

This is the work we do as part of advisory engagements with our clients each year, and it is the work that produces the savings that make the engagement pay for itself. If you don't have someone running this process for you, the cost of the items missed compounds — not just in tax dollars, but in the structural choices the year locks in regardless.

Beaconshire Advisory handles year-end tax planning as part of our tax advisory engagements. The right time to start is October. The right time to find the right advisor is now.