Year-End Tax Planning: Why Starting in September Beats Starting in December
Most people treat year-end tax planning as a December task, when really, December is too late.
Most people treat year-end tax planning as a December task.
Every year, the same pattern plays out: the holidays approach, someone mentions taxes, and a scramble begins to find deductions, make contributions, and arrange finances before December 31st. Some years it works out reasonably well. More often, the best opportunities have already closed by the time the conversation starts.
The advisors who consistently deliver the best year-end outcomes for their clients don't do anything magical in December. They started the conversation in September when there were still four months of runway to make decisions thoughtfully, coordinate with a CPA, and execute without pressure.
This post is about what that looks like in practice. We’ll touch on five specific moves worth making right now, while they can still make a meaningful difference, and why each one loses value the longer you wait.
Why September? The Case for Starting Now
Before getting into specific moves, it's worth understanding why timing matters so much in year-end tax planning.
Several of the most valuable tax-saving strategies require time, not just money.
Retirement account establishment deadlines. A Solo 401(k) plan must be established by December 31st of the year you want to make contributions for that year. You can fund the account as late as your tax filing deadline, but the plan itself must exist before the calendar year closes. A business owner who realizes in December that a Solo 401(k) would save them thousands in taxes has a narrow window (sometimes just days) to set one up. Starting in September gives months of unhurried setup time.
Income and deduction timing. Deciding whether to accelerate income into this year or defer it to next requires visibility into your full-year picture. In September, you have eight months of actual data and four months of projections. In December, you have eleven months of actual data and three weeks to act. The decisions are the same; the quality of the information and the time to execute are very different.
Tax-loss harvesting. Selling investments at a loss to offset capital gains requires time to reinvest in appropriate replacement securities, navigate wash-sale rules, and coordinate with your overall portfolio strategy. Harvesting losses in September leaves room for multiple rounds of review. Harvesting in December is a compressed, reactive exercise.
Estimated tax payments. The Q3 estimated payment was due September 15th. The Q4 payment is due January 15th. Understanding your full-year income picture now, while you can still adjust the Q4 payment, is far preferable to calculating it after the fact.
September is not too early. December is, for many of these moves, genuinely too late.
Move #1: Maximize Your Retirement Contributions
This is the single most powerful tax-reduction tool available to most of our clients, and the one most consistently underutilized.
Every dollar contributed to a pre-tax retirement account reduces your taxable income by that same dollar. For someone in the 24% federal tax bracket, a $10,000 contribution saves up to $2,400 in federal income taxes. For someone in the 32% bracket, it saves up to $3,200. Add state income taxes and the savings grow further.
For business owners: The options are broader and the planning more nuanced.
A SEP IRA allows contributions of up to 25% of net self-employment income, with a 2026 maximum of $72,000. Contributions can be made as late as the tax filing deadline including extensions, giving you flexibility on timing. Simple to administer, no plan document required.
A Solo 401(k) is available to self-employed individuals with no full-time employees other than a spouse. It allows both an employee contribution of up to $24,500 and an employer profit-sharing contribution of up to 25% of compensation, with a combined maximum of $72,000 ($80,000 with catch-up for those 50-59 and 64+ and $83,250 with catch up for those 60-63). The Solo 401(k) offers the highest potential contribution ceiling for high-earning sole proprietors, but again, the plan must be established by December 31st. If you don't currently have one, the evaluation needs to happen now.
A SIMPLE IRA works well for small businesses with employees, offering lower contribution limits but simpler administration than a 401(k).
For everyone approaching age milestones: If you'll be 50 or older by December 31st, you're eligible for catch-up contributions that increase your limits significantly. If you'll be 60, 61, 62, or 63, SECURE 2.0 created an enhanced catch-up provision that allows even higher limits. Confirm whether these apply to you and whether you're taking full advantage.
For military members: Log into your TSP account and confirm your current contribution rate. If you're not on pace to hit the annual contribution limit before December 31st, calculate what rate adjustment would get you there, and make it now. The four months remaining in the year are enough to meaningfully close a contribution gap if you act today rather than in November.
Move #2: Tax-Loss Harvesting
Tax-loss harvesting is the practice of selling investments that have declined in value to realize a capital loss, which can then be used to offset capital gains and reduce your overall tax liability.
The mechanics: if you've realized capital gains elsewhere in your portfolio this year (from selling investments that went up in value, receiving mutual fund distributions, or similar events), those gains create a tax liability. Losses realized from selling other positions offset those gains dollar-for-dollar. If losses exceed gains, up to $3,000 of excess losses can be deducted against ordinary income in a given year, with additional losses carried forward to future years.
The September advantage is meaningful. Harvesting losses in September gives you time to:
Evaluate your full portfolio picture with Q3 data before making decisions. Reinvest the proceeds in appropriate replacement securities without triggering the wash-sale rule, which disallows a loss if you repurchase the same or "substantially identical" security within 30 days before or after the sale. Coordinate with your overall income picture to ensure the harvesting strategy makes sense given your full-year tax situation.
December harvesters face all of the above with a compressed timeline that makes thoughtful execution difficult.
For business owners: A profitable business year makes tax-loss harvesting more valuable, because you have gains to offset. Review your personal investment accounts alongside your business income picture for the most complete view.
For military members: If you have investments outside your TSP (taxable brokerage accounts, inherited investments, deployment savings that were invested) this strategy may apply. Coordinate with your financial planner to review your portfolio for harvesting opportunities.
Deduction timing can shift significant tax liability between years.
Move #3: Income and Deduction Timing
Within certain limits, you have meaningful control over when income is recognized and when deductions are taken. That timing can shift significant tax liability between years.
This strategy is most powerful when you know approximately which tax bracket you'll land in for the current year and have a clear projection for next year. If you expect a higher income year in 2026 than 2027, accelerating deductions into 2026 and deferring income to 2027 reduces your overall tax burden across both years.
For business owners:
Accelerating deductions: Business expenses paid before December 31st are generally deductible in the current year. This includes equipment purchases, professional services, prepaid business insurance, and charitable contributions made through the business. Section 179 and bonus depreciation allow certain business assets to be fully deducted in the year of purchase rather than depreciated over time. Knowing this makes the timing of equipment purchases a tax planning decision, not just an operational one.
Deferring income: If you're near a tax bracket threshold, deferring a year-end invoice or delaying a receivable into January shifts that income to the following year. This requires careful cash flow planning. For businesses with some flexibility on billing timing, it's a legitimate and legal strategy.
For military retirees with encore careers: Coordinating the timing of TSP or IRA distributions with earned income is a meaningful planning opportunity. A year with lower earned income may be a better year to take a distribution; a year with higher earned income may be better served by deferring. This kind of multi-year income management is exactly where working with a fee-only financial planner alongside a CPA produces its highest value.
Move #4: Charitable Giving Strategy
For clients who give charitably, the method and timing of giving can produce meaningfully different tax outcomes. The strategies that work best require advance planning.
Qualified Charitable Distributions (QCDs): Available to IRA owners age 70½ and older. A QCD allows you to transfer money directly from your IRA to a qualified charity. The current limit is up to $111,000 per year as of 2026 and married couples are each allowed to donate up to the individual limit for a total of $222,000. In addition to the annual limit, each tax payer can make a one time QCD donation up to $55,000 to a charitable remainder trust or charitable gift annuity. The key benefit: the distribution satisfies your required minimum distribution obligation but is excluded from your taxable income entirely. This is more tax-efficient than taking the RMD, paying taxes on it, and then making a charitable gift, particularly for clients who don't itemize deductions.
Donor-Advised Funds (DAFs): A donor-advised fund allows you to make a large charitable contribution in a high-income year, capture the full deduction immediately, and then distribute the funds to specific charities over time. This is particularly useful in years when income is elevated (a business sale, a large bonus, a one-time distribution) where bunching charitable giving into a single year maximizes the deduction's impact.
Bunching strategy: For clients whose annual charitable giving doesn't exceed the standard deduction threshold, combining two years of planned giving into one year can push total itemized deductions above the standard deduction. This can make the giving deductible in a way that wouldn't otherwise be possible.
All of these strategies require setup time. A donor-advised fund can't be opened retroactively. A QCD requires coordination with the IRA custodian. September provides the time to evaluate which approach fits your situation and execute it cleanly.
Move #5: A Year-End Review Checklist
Beyond the four specific strategies above, here is a practical September checklist for military families and business owners:
For business owners:
Confirm retirement account contribution pace, and establish any new plans before December 31st
Calculate Q4 estimated tax payment (due January 15th)
Evaluate business purchases for Section 179 or bonus depreciation
Assess whether an S-corp election for 2027 should be evaluated now, before the March 15th filing deadline
Coordinate with your CPA on income deferral or acceleration decisions
For military members:
Confirm TSP contribution rate is on pace for the annual limit
Review Roth vs. Traditional TSP election in light of this year's income and promotion timeline
Update beneficiary designations on all accounts if any life changes have occurred
Review VA disability rating status and any pending claims
Coordinate pension income with any other income sources for bracket management
For everyone:
Review withholding. If you received a large refund last year, consider adjusting to improve cash flow; if you owed a large amount, adjust to avoid underpayment penalties
Review all beneficiary designations on retirement accounts, life insurance, and other financial accounts
Confirm that estate documents like your will, power of attorney, healthcare directive are current
The Bottom Line
The gap between good year-end tax outcomes and great ones is almost always a function of when the conversation started, not how sophisticated the strategies were.
Starting in September means four months of thoughtful decision-making, coordinated execution, and unhurried planning. Starting in December means a compressed scramble through a narrowed set of options.
At Clear Insight Wealth Management, we work with business owners and military families on year-round financial planning because the best outcomes are built over months, not days. If you'd like to make sure your 2026 year-end picture is as strong as it can be, we'd love to start that conversation now.
