Most year-end tax planning advice arrives too late for the moves that require months of preparation. But several high-value strategies remain available deep into December -- some right up to December 31, and a few that extend into mid-January or even April. This checklist organizes the remaining moves by their actual deadlines so you can prioritize what still matters.
The critical distinction is between moves that must happen by December 31 and those with later deadlines that people mistakenly rush. Confusing the two either costs money or creates unnecessary stress. Check each strategy's actual deadline before acting.
Tax planning is a year-round exercise, and the best moves -- Roth conversions, income shifting, entity elections -- require lead time that December cannot provide. But several strategies remain viable in the final weeks of the year, and missing them means waiting 12 months for the next opportunity.
The critical distinction is between moves that must happen by December 31 and those with later deadlines that people mistakenly rush. A 401(k) contribution increase, for example, must hit payroll before year-end. An IRA contribution for 2027, on the other hand, can wait until April 15, 2028. Confusing the two either costs money or creates unnecessary stress.
December 31 Deadline: Moves That Cannot Wait
Max Out Your 401(k) or 403(b)
The 2027 employee contribution limit is projected at $24,050 (up from $23,500 in 2026, pending IRS inflation adjustment). If you are 50 or older, the catch-up contribution adds $7,500 for a total of $31,550. For those aged 60 to 63, the enhanced catch-up under SECURE 2.0 allows $11,250 for a total of $35,300. Technical detail
Check your year-to-date contributions on your most recent pay stub. If you are behind, calculate how many paychecks remain and increase your deferral percentage to close the gap. Most employers process 401(k) changes within one to two pay periods, so submitting the change in the first week of December typically leaves enough cycles to catch up.
Dollar example: If you have contributed $18,000 through November and have two remaining biweekly paychecks, you need to defer $3,025 per paycheck to reach the $24,050 limit. That requires a temporary spike in your deferral percentage, which you can reset in January.
Harvest Investment Losses
- Pays tax on $12,000 in realized capital gains
- At 23.8% combined rate: $2,856 in capital gains tax
- $15,000 in unrealized losses remain on paper, producing no current tax benefit
- $15,000 loss offsets $12,000 gain completely
- Remaining $3,000 loss deducts against ordinary income
- At 24% bracket, the ordinary income deduction saves another $720
- Reinvests in a similar (not identical) fund to maintain market exposure
Capital losses first offset capital gains dollar for dollar, including both short-term and long-term gains. Remaining losses offset up to $3,000 of ordinary income ($1,500 if married filing separately). Unused losses carry forward indefinitely. Technical detail
The wash sale rule under IRC Section 1091 prevents you from claiming the loss if you repurchase a "substantially identical" security within 30 days before or after the sale. This means:
- You cannot sell a mutual fund at a loss and buy the same fund back within 30 days
- You can sell a fund at a loss and immediately buy a similar but not identical fund (e.g., switch from one S&P 500 index fund to a total market fund)
- The rule applies across all your accounts, including your IRA and your spouse's accounts
Dollar example: You hold a stock position with $15,000 in unrealized losses and have $12,000 in realized capital gains from earlier in the year. Harvesting the loss eliminates the $12,000 gain (saving roughly $2,856 at the 23.8% combined rate) and gives you a $3,000 deduction against ordinary income. At the 24% bracket, that is another $720 in savings.
Charitable Contributions: Cash and Appreciated Stock
Cash donations must clear or be charged by December 31. Donations of appreciated stock must be transferred to the charity or donor-advised fund (DAF) by year-end, and brokerage transfers can take five to seven business days, so mid-December is the practical deadline for stock gifts.
If you are considering a bunching strategy -- concentrating multiple years of giving into a single year to exceed the standard deduction -- December is when you execute the lump-sum contribution. A DAF is the practical vehicle: you contribute the full bunched amount in the bunching year, claim the deduction, and then distribute grants to charities over the following years.
The charitable deduction limit for cash gifts is 60% of adjusted gross income (AGI). For appreciated assets held more than one year, it is 30% of AGI. Non-itemizers can deduct cash contributions up to $1,000 ($2,000 for married filing jointly) starting in 2026 under OBBBA. Technical detail
Pay State and Local Taxes Early (If Bunching)
If you are bunching itemized deductions, paying your January state estimated tax payment or your property tax bill before December 31 pulls that deduction into the current year. The SALT deduction is capped at $40,000 for married filing jointly ($20,000 for married filing separately) under OBBBA. Technical detail
This only helps if your total SALT payments for the year are below the cap and the early payment pushes you over the standard deduction threshold for itemizing. If you are already at the cap, paying early accomplishes nothing.
Accelerate or Defer Income
If you have any control over the timing of income -- a bonus, a freelance invoice, a stock option exercise -- the last weeks of December are when you decide which year to recognize it.
- Accelerate income into this year if you expect to be in a higher bracket next year, or if you have losses to offset the additional income
- Defer income to next year if you expect lower income, anticipate a life event that will reduce your tax rate, or want to stay below a threshold that triggers phase-outs (IRMAA, Roth IRA eligibility, premium tax credits)
For employees, bonus timing is typically controlled by the employer. For self-employed individuals, sending an invoice on December 28 versus January 2 can shift thousands of dollars between tax years. Cash-basis taxpayers recognize income when received, not when billed, so the timing of payment matters.
Bunch Medical Expenses
Medical expenses are deductible only to the extent they exceed 7.5% of AGI. IRC Section 213(a). If you have significant medical costs and are near the threshold, scheduling and paying for elective procedures, dental work, or vision correction before December 31 can push you over.
Dollar example: Your AGI is $100,000. The 7.5% floor is $7,500. You have $6,000 in medical expenses so far this year. A $4,000 dental procedure in December brings your total to $10,000, creating a $2,500 deduction. At the 22% bracket, that saves $550. If you wait until January, the $4,000 starts fresh against next year's floor and may produce no deduction at all.
Q4 Estimated Tax Payment (January 15)
The fourth quarter estimated tax payment for the current tax year is due January 15 of the following year. If you underpaid earlier quarters, this is your last chance to true up before penalties begin to accrue. Technical detail
If you owe a large balance, an alternative is to increase your W-2 withholding in December. Federal withholding is treated as if paid evenly throughout the year regardless of when it was actually withheld, which means a December withholding spike can retroactively cover underpayment for earlier quarters. This trick does not work with estimated payments, which are credited on the date paid.
April 15 Deadline: Moves That Are Not Actually Urgent in December
IRA Contributions
You have until the tax filing deadline (April 15, 2028 for the 2027 tax year) to make traditional or Roth IRA contributions. The 2027 limit is expected at $7,000 ($8,000 if 50 or older). IRC Section 219(b)(5)(A) sets the IRA contribution limit. Section 219(b)(5)(B) provides the age-50 catch-up. There is no advantage to rushing this into December unless you want the money invested sooner for growth.
HSA Contributions
Health Savings Account contributions can also be made up to the April 15 filing deadline. For 2027, limits are projected at approximately $4,300 for individual coverage and $8,550 for family coverage ($1,000 catch-up if 55 or older). You must have had a qualifying High Deductible Health Plan during the applicable months.
SEP-IRA Contributions
Self-employed individuals and small business owners can contribute to a SEP-IRA up to the tax filing deadline, including extensions (October 15 if you file an extension). The limit is 25% of net self-employment income, up to $70,000 (2027 projected). This is the most generous deadline on the list and rarely requires December action.
| Deadline | Move |
|---|---|
| Mid-December | Donate appreciated stock (allow 5-7 business days for transfer) |
| Last trading day of December | Execute tax-loss harvesting trades (T+1 settlement) |
| December 31 | Max out 401(k)/403(b) via payroll |
| December 31 | Make charitable cash contributions |
| December 31 | Pay state taxes early (if bunching SALT) |
| December 31 | Accelerate or defer income |
| December 31 | Pay medical expenses (if bunching) |
| January 15 | Q4 estimated tax payment |
| April 15 | IRA and HSA contributions for prior year |
| April 15 (or Oct 15 with extension) | SEP-IRA contributions for prior year |
If your CPA is unavailable in December, that is itself a data point worth considering when you evaluate the relationship. Year-end planning is one of the most valuable services a proactive CPA provides. A personalized projection showing your exact bracket, phase-out proximity, and room for each strategy is often worth thousands of dollars more than a generic checklist.
A CPA with access to your full-year data can run a projection showing your exact bracket, where you stand against phase-out thresholds, and how much room you have for each strategy. The difference between a generic checklist and a personalized projection is often thousands of dollars.
Specifically, a December tax planning session should answer:
- Whether harvesting losses creates a net benefit after accounting for your expected future gains and the wash sale rule
- The exact dollar amount of charitable bunching that pushes you past the standard deduction
- Whether accelerating or deferring income keeps you below IRMAA thresholds, ACA subsidy cliffs, or credit phase-outs
- How much 401(k) room remains and whether a mega backdoor Roth (if your plan allows it) is worth executing before year-end
If your CPA is unavailable in December -- as many are -- this is itself a data point worth considering when you evaluate the relationship. Year-end planning is one of the most valuable services a proactive CPA provides.