Tax Moves Worth Making Before December 31

Tax planning is fundamentally a timing game. The decisions that reduce your April bill aren't made in April — they're made in the preceding November and December, when you can still act on information about how the current year is shaping up. After December 31, the door closes on most meaningful moves. You're left filing a return that reflects choices you didn't know you were making.

The year-end tax checklist isn't complicated, but it requires knowing where you stand. That means pulling up your most recent pay stubs, any 1099 income, and your brokerage statements before the calendar flips. Doing it from memory in March produces guesses, not optimization.

Retirement Account Contributions: The Last Chance Window

401(k) contributions must be made by December 31 — they come from payroll, and payroll runs on the employer's schedule. If you want to maximize your contribution for the year (the 2024 limit was $23,000, $30,500 for those 50 and older), the time to adjust your contribution rate is early enough in the year's final weeks that your last payroll can include the full amount. Many people realize in December that they've left contribution room on the table and can't get it back.

IRA contributions work differently. You have until the tax filing deadline — typically April 15 — to make a prior-year IRA contribution. So technically you have until mid-April to contribute to an IRA for the previous tax year. But this grace period is frequently confused with 401(k) rules, leading people to wrongly believe they missed the IRA deadline. They haven't.

HSA contributions also have until April 15 for the prior year, but your HSA administrator needs to know which year to apply it to, so make sure you designate properly. The 2024 HSA limit was $4,150 for individuals and $8,300 for families. If you haven't maxed it, the tax benefit — contributions are triple-tax-advantaged — is among the best available in the tax code.

Tax-Loss Harvesting Before Year-End

Tax-loss harvesting means selling investments that are worth less than you paid for them to realize a capital loss, which can offset capital gains elsewhere in your portfolio. If you had a year with significant capital gains — you sold appreciated stock, a property, or cryptocurrency — the losses from other positions can reduce the taxable amount.

Capital losses can offset capital gains dollar for dollar. Beyond that, you can use up to $3,000 of net capital losses to offset ordinary income, and any excess loss carries forward to future years. For someone in the 22% federal bracket with $5,000 in net losses, the tax benefit is potentially $1,100 in the current year ($3,000 at 22%) plus the $2,000 carryforward for next year.

The wash-sale rule is the critical constraint: you cannot buy back the same or a substantially identical security within 30 days before or after selling it for a loss, or the loss is disallowed. You can immediately reinvest the proceeds in a similar (but not identical) fund — for example, selling a Vanguard Total Market ETF and buying a Schwab Total Market ETF — to maintain market exposure without triggering the wash-sale rule.

Accelerating Deductions, Deferring Income

If you're close to the threshold where itemizing beats the standard deduction, December is the time to either push yourself over by accelerating deductible expenses, or to acknowledge you won't get there and take the standard deduction without adding additional charitable gifts that won't produce a tax benefit.

Deduction acceleration strategies include making your January mortgage payment in December (the interest portion becomes deductible in the current tax year), prepaying a state tax estimate if you pay quarterly, and making charitable donations before December 31 rather than in January. None of these create new deductions — they shift the timing to maximize the benefit in the year where it helps most.

On the income side: if you're a freelancer or self-employed, you have limited ability to defer income — but you can delay sending invoices in late December if the payment won't arrive until January anyway. Income is generally taxed in the year received, not the year billed. If you know a year-end bonus is coming, you can't easily defer it, but a bonus that vests in early January is effectively income next year.

Charitable Giving Strategies for December

For itemizers, donating appreciated securities directly to charity is substantially more efficient than donating cash. If you've held stock with significant gains for more than a year, donating the shares rather than selling them first allows you to deduct the full fair market value while completely avoiding capital gains tax on the appreciation. A share of stock bought at $20 and now worth $100 — if sold — produces $80 in taxable gain. If donated directly, you deduct $100 and pay zero capital gains tax.

Donor-advised funds (DAFs) are a useful tool for bunching. If you don't give enough annually to exceed the standard deduction, but you plan to give over multiple years, a DAF lets you front-load several years of giving into one lump contribution — taking a large deduction this year — while distributing the funds to charities over time on your own schedule. Fidelity Charitable and Schwab Charitable both have DAF minimums starting around $5,000.

Self-Employed: Timing Business Expenses

If you're self-employed and had a higher income year, December is the time to make business purchases you were planning to make anyway — equipment, software subscriptions, professional development, office supplies. Deductible business expenses reduce your net self-employment income, which reduces both income tax and self-employment tax (the latter at 15.3% on the first $168,600 of net SE income in 2024). The tax benefit of a $1,000 legitimate business expense can be $350 or more in a higher bracket with SE tax.

Self-employed retirement contributions — to a SEP-IRA, Solo 401(k), or SIMPLE IRA — are another powerful lever. SEP-IRA contributions can be made up to the tax filing deadline including extensions, allowing you to contribute up to 25% of net self-employment income, up to $69,000 in 2024. This is often the largest single year-end tax move available to solo business owners.

Check Your Withholding Before January

Year-end is also the right time to check whether your withholding was approximately correct. Use your most recent pay stub to estimate your year-end W-2, add any 1099 income, subtract your expected deductions, and run a rough tax calculation. If you're going to owe significantly more than $1,000 beyond what was withheld, you might owe an underpayment penalty.

If you're significantly overwithholding — getting a large refund every year — December is the time to file a new W-4 with your employer to reduce withholding going forward. A large refund isn't free money; it's an interest-free loan to the IRS. Every $3,000 annual refund is $250 per month you could have in your own account all year.

None of this requires a tax professional to implement — though a professional is valuable if your situation involves complexity. What it requires is looking at your finances before the year ends rather than after. The difference between proactive and reactive tax planning isn't access to secret strategies; it's timing.