Year-End Tax Planning Starts Now: A Month-by-Month Guide for September Through December

Year-end tax planning is not a December activity. The most valuable moves require lead time -- tax-loss harvesting needs 31 days to clear the wash sale window, Roth conversions need processing time before December 31, and 401(k) contribution changes need at least one payroll cycle to take effect. Starting in September gives you four months to act deliberately instead of scrambling.

This guide breaks the final quarter of the tax year into monthly action items, each with specific deadlines, dollar thresholds, and references to deeper content where relevant. The numbers below reflect 2026 tax law, including changes enacted by the One Big Beautiful Bill Act (OBBBA).

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September: Assess Where You Stand

September is diagnostic. You have eight months of income data and four months to adjust. The goal is to project your full-year tax picture so every decision in October through December is based on real numbers, not guesses.

Review Your Withholding

Pull your most recent pay stub and look at the year-to-date federal tax withheld. Multiply your per-period withholding by the number of remaining pay periods and add it to the year-to-date figure. Compare that total to your projected tax liability for the full year. If you are going to be short by more than $1,000, you owe estimated tax or need to increase your W-4 withholding.

Technical detail

IRC Section 6654(e)(1). No penalty applies if you owe less than $1,000 after subtracting withholding and refundable credits.

Withholding adjustments have an advantage over estimated payments: the IRS treats withheld taxes as paid evenly throughout the year, even if you increase withholding only in the final quarter.

Technical detail

IRC Section 6654(g). Taxes withheld are deemed paid in equal installments on each quarterly due date, regardless of when they were actually withheld.

That means a December withholding bump can retroactively cover shortfalls from earlier quarters -- estimated payments cannot do this.

Project Full-Year Income

Build a rough projection of your full-year adjusted gross income (AGI). Include salary, bonuses (check with your employer on timing), investment income, rental income, K-1 income, and any expected capital gains from sales you plan to make. This number drives nearly every decision below: whether you should harvest losses, whether charitable bunching makes sense, whether a Roth conversion fits, and how much room you have in your current tax bracket.

For 2026, the key bracket thresholds for married filing jointly are:

Tax Foundation, 2026 Federal Income Tax Brackets. Standard deduction for MFJ: $32,200; Single: $16,100.

Check Estimated Payment Adequacy

If you make quarterly estimated payments, September 15 is the due date for Q3. Before you write that check, verify you are meeting one of the safe harbor thresholds: 90% of your current-year tax liability, or 100% of your prior-year tax (110% if your prior-year AGI exceeded $150,000).

Technical detail

IRC Section 6654(d). The 110% threshold applies to taxpayers with AGI above $150,000 ($75,000 if married filing separately).

For a full walkthrough of estimated payment calculations, see Estimated Tax Payments: Who Owes Them, When They're Due, and How to Calculate.

September key date: September 15, 2026 -- Q3 estimated tax payment due.

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October: Harvest Losses, Review Investments

October is the action month for your investment portfolio. You need a full 31 days before December 31 for any tax-loss harvesting to clear the wash sale window, which makes early-to-mid October the practical deadline.

Tax-Loss Harvesting

Tax-loss harvesting means selling investments that are currently below your purchase price to realize a capital loss. Those losses offset capital gains dollar-for-dollar, and up to $3,000 of excess losses ($1,500 if married filing separately) can offset ordinary income each year. IRC Section 1211(b). Unused losses carry forward indefinitely under IRC Section 1212(b).

The strategy only works if you avoid the wash sale rule. Under IRC Section 1091, if you buy "substantially identical" securities within 30 days before or after a loss sale, the loss is disallowed. The disallowed loss gets added to the basis of the replacement shares, so it is not permanently lost -- but it is deferred, which defeats the purpose of year-end harvesting.

**Practical implications for October timing:**

• Sell the losing position no later than early November to ensure the 30-day post-sale window closes before December 31.
• If you want to stay invested in the same market segment, buy a similar (but not substantially identical) fund immediately. For example, sell an S&P 500 index fund at a loss and buy a total stock market fund. The IRS has not defined "substantially identical" with bright-line rules for mutual funds, but tracking different indexes is generally accepted as safe.
  Technical detail

  IRS Revenue Ruling 2008-5 addresses the basis adjustment mechanics for wash sales but does not define "substantially identical" for index funds.
• After 31 days, you can repurchase the original position if you prefer it.

For investors with net long-term capital gains, harvesting short-term losses is especially valuable because short-term losses first offset short-term gains (taxed at ordinary rates up to 37%) before netting against long-term gains (taxed at 0%, 15%, or 20%). IRC Section 1(h). The 2026 0% long-term capital gains rate applies to taxable income up to $98,900 MFJ / $49,450 single.

Review Appreciated Stock for Charitable Donations

While reviewing your portfolio, flag any highly appreciated long-term holdings you might donate rather than sell. Donating appreciated stock held for more than one year lets you deduct the full fair market value while avoiding capital gains tax entirely. The deduction limit for appreciated property donations is 30% of AGI.

Technical detail

IRC Section 170(b)(1)(C). The 30% limit applies to contributions of capital gain property to public charities. Any excess carries forward for up to five years.

This sets up the charitable giving decisions you will finalize in November.

October key date: Begin tax-loss harvesting by mid-October to ensure 30-day wash sale window clears by mid-November.

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November: Charitable Giving and Roth Conversions

November is decision month for two of the highest-impact year-end strategies: charitable contributions and Roth conversions. Both have December 31 deadlines, but both require planning time.

Charitable Giving: Bunch vs. Spread

The 2026 standard deduction is $32,200 for married filing jointly and $16,100 for single filers. If your total itemized deductions (including state and local taxes capped at $10,000, mortgage interest, and charitable contributions) do not exceed the standard deduction, you get zero incremental tax benefit from charitable gifts.

Bunching solves this. Instead of giving $8,000 per year for three years ($24,000 total, never enough to itemize), you give $24,000 in a single year and take the standard deduction in the other two. The total charitable giving is identical, but the tax savings can be several thousand dollars.

Starting in 2026, the OBBBA introduced a 0.5% AGI floor on charitable deductions for itemizers. Only the amount of your charitable contributions exceeding 0.5% of AGI is deductible.

Technical detail

OBBBA Section 110502. For a taxpayer with $200,000 AGI, the first $1,000 of charitable contributions produces no deduction.

Additionally, taxpayers in the 37% bracket have their charitable deduction benefit capped at 35%. OBBBA Section 110501.

There is also a new provision for non-itemizers: a deduction of up to $1,000 for individuals ($2,000 MFJ) for cash donations made directly to operating charities. Contributions to donor-advised funds do not qualify for this non-itemizer deduction. OBBBA Section 110503.

Donor-Advised Fund (DAF) Funding

If you plan to bunch, a donor-advised fund is the most flexible vehicle. You contribute cash or appreciated securities to the DAF, take the full deduction in the contribution year, and then distribute grants to your chosen charities over time. The deduction limits are the same as for direct gifts to public charities: 60% of AGI for cash, 30% for appreciated property. IRC Section 170(b)(1)(A). DAF sponsors are classified as public charities.

Fund the DAF before December 31 of the bunching year. There is no requirement to distribute the funds to end charities by year-end -- the deduction is locked in upon contribution to the DAF.

Qualified Charitable Distributions (QCDs) for Those 70 1/2 and Older

If you are 70 1/2 or older, a qualified charitable distribution lets you send up to $111,000 per person directly from your IRA to a qualifying charity. The distribution is excluded from your gross income entirely -- it never appears as taxable income.

Technical detail

IRC Section 408(d)(8). The $111,000 limit applies per individual for 2026 and is indexed for inflation under SECURE 2.0 Act Section 307.

QCDs are often superior to deducting a charitable contribution because:

• The income exclusion reduces your AGI, which affects Social Security taxation thresholds, Medicare IRMAA surcharges, and other AGI-dependent calculations.
• You do not need to itemize to benefit from a QCD. It works equally well for standard deduction filers.
• A QCD can satisfy all or part of your required minimum distribution for the year.

The distribution must go directly from the IRA custodian to the charity. If the funds touch your personal account first, the QCD treatment is lost.

### Roth Conversion Window

Roth conversions must be completed by December 31 to count for the current tax year. There is no extension.

Technical detail

IRC Section 408A(d)(3). Unlike IRA contributions, which can be made until the filing deadline, conversions are irrevocable and must occur by calendar year-end.

November is the time to decide whether a conversion makes sense, because you need your near-final income projection (from the September assessment, updated for any changes) to determine how much room you have in your current bracket. Converting $50,000 that pushes you from the 22% bracket into the 24% bracket has a different calculus than converting $50,000 that stays entirely within the 12% bracket. For a detailed walkthrough of conversion math and bracket optimization, see Roth Conversions Explained.

Key considerations before converting:

• You need cash on hand to pay the tax on the conversion. Paying the tax from the conversion itself reduces the amount that enters the Roth and, if you are under 59 1/2, triggers a 10% early withdrawal penalty on the withheld amount.
• Once converted, you cannot reverse it. The recharacterization option was eliminated by the Tax Cuts and Jobs Act in 2018.
• If you are subject to RMDs, you must take your full RMD for the year before converting any additional amount.

November key dates: Make charitable giving decisions early enough to process stock transfers (allow 5-10 business days for appreciated stock donations). Begin Roth conversion paperwork.

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December: Final Moves and Hard Deadlines

December is execution. Most year-end tax strategies have an absolute December 31 cutoff, and several require lead time.

### Max Out Your 401(k)

The 2026 employee contribution limit for 401(k), 403(b), and most 457 plans is $24,500. IRC Section 402(g). IRS Notice 2025-XX confirmed the 2026 limit. The catch-up contribution for workers age 50 and older is an additional $8,000, bringing the total to $32,500. Workers aged 60 through 63 get a higher catch-up limit of $11,250 under SECURE 2.0, for a total of $35,750. SECURE 2.0 Act Section 109.

If you are behind on contributions, contact your payroll department immediately. Most plans require at least one full payroll cycle to process a contribution rate change. If you have two December pay dates, you may be able to allocate a large percentage of your final paychecks to the 401(k) -- but this requires coordination with your employer's plan administrator, and not all plans allow mid-period changes.

Important for high earners: Starting in 2026, participants who earned more than $150,000 in FICA wages in the prior year must make catch-up contributions on a Roth (after-tax) basis. SECURE 2.0 Act Section 603. This does not affect the base $24,500 contribution -- only the catch-up portion.

IRA Contributions

Traditional and Roth IRA contribution limits for 2026 are $7,500 per person ($8,500 with the age-50 catch-up). IRC Section 219(b)(5)(A). Unlike 401(k) contributions, IRA contributions can be made until the April 15, 2027, filing deadline. There is no urgency to fund these in December unless you want the money invested and compounding sooner.

Make the Final Estimated Tax Payment (If Applicable)

The Q4 estimated tax payment is due January 15, 2027 -- but if you file your return and pay the balance due by January 31, 2027, no Q4 estimated payment is required. IRC Section 6654(h). If you will not file that early, make the Q4 payment by January 15 or increase your December withholding to cover the gap (remember: withholding is treated as paid ratably throughout the year).

Prepay State Income Taxes (If Bunching Itemized Deductions)

If you are bunching deductions this year and your total state and local tax (SALT) deduction will not exceed the $10,000 cap, consider making your Q4 state estimated payment before December 31 instead of January 15. This pulls the deduction into the current year. IRC Section 164(b)(6). The $10,000 SALT cap was made permanent by the OBBBA. This strategy only helps if (a) you are itemizing, and (b) your total SALT deduction is not already at $10,000.

Last-Minute Deduction Opportunities

Several deductions require only a December 31 deadline:

• Medical expenses above 7.5% of AGI are deductible if you itemize. IRC Section 213(a). The 7.5% floor was made permanent by the OBBBA. If you are close to the threshold, scheduling and paying for elective procedures, dental work, or vision care before year-end can push you over.
• Business equipment purchases can be fully expensed under IRC Section 179 (up to $1,270,000 for 2026) or bonus depreciation if placed in service by December 31. IRC Section 168(k).
• Student loan interest is deductible up to $2,500 above the line, regardless of whether you itemize, subject to income phaseouts. IRC Section 221.

Annual Gift Tax Exclusion

The 2026 annual gift tax exclusion is $19,000 per recipient ($38,000 for married couples making split gifts). IRC Section 2503(b). These gifts do not reduce your income tax, but if you are implementing an estate plan that involves annual gifting, December 31 is the deadline for 2026 gifts. Unused exclusion does not carry forward to the next year.

December key dates:

• December 31 -- Deadline for Roth conversions, charitable contributions, 401(k) contributions, tax-loss harvesting, and annual gifts.
• January 15, 2027 -- Q4 estimated tax payment due (or file and pay in full by January 31).

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Quick-Reference Calendar

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Key Dollar Thresholds for 2026

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Frequently Asked Questions

What if I missed September and October? Is it too late to do year-end planning in December?

No, but your options narrow. Roth conversions, 401(k) contributions, and charitable gifts can all still happen in December. What you lose is the ability to tax-loss harvest with a clean wash sale window (you would need to wait 31 days before repurchasing, pushing you into late January) and the luxury of adjusting withholding over multiple pay periods. If you are starting in December, focus on the moves that only require writing a check or initiating a transfer.

Should I harvest losses even if I have no capital gains this year?

Yes, if you have unrealized losses worth realizing. Up to $3,000 in net capital losses can offset ordinary income each year, and any excess carries forward indefinitely. IRC Section 1212(b). If you are in the 24% bracket, a $3,000 ordinary income offset saves $720 in federal tax. Over several years of carryforward, the cumulative benefit can be meaningful.

How do I decide between a QCD and a regular charitable deduction?

If you are 70 1/2 or older and have IRA assets, the QCD is almost always superior. It reduces your AGI (a regular deduction does not -- it only reduces taxable income). Lower AGI means lower Social Security taxation, lower Medicare premiums, and lower exposure to the 3.8% net investment income tax. The main exception is if you have appreciated stock you want to donate -- QCDs can only come from IRAs, not brokerage accounts, so donating the stock directly is more efficient for that specific asset.

Can I do a Roth conversion and a QCD in the same year?

Yes, but the order matters. If you have an RMD for the year, the first dollars out of your IRA satisfy the RMD before they count as a conversion. IRS Publication 590-B. The first distributions from an IRA in any year are applied toward the RMD. You can use a QCD to satisfy the RMD (keeping it out of taxable income), then convert additional amounts to Roth. This is a powerful combination for retirees who are charitably inclined and want to reduce future RMDs simultaneously.

Do I need a CPA for year-end tax planning, or can I do this myself?

The month-by-month steps above are designed for self-implementation. Where a CPA adds value is in the projections -- modeling how a Roth conversion interacts with your Social Security taxation, IRMAA thresholds, and state taxes, or determining the optimal bunching cadence for charitable giving over a multi-year period. If your AGI is above $200,000, you have multiple income types, or you are within two years of retirement, the planning session typically pays for itself in the first year.