Dollar figures in this piece are for tax year 2026.
Sort every year-end idea into one of two piles. The first pile has to be finished by December 31, 2026: charitable gifts, equipment that must be in service, 401(k) salary deferrals, a Roth conversion, loss sales and annual gifts. The second pile can wait for the filing deadline: IRA, HSA and SEP contributions, plus the last estimated payment in January. Confusing the piles is how people rush a deposit that could have waited or miss a deadline that could not.
It is early October, so there are about twelve weeks left on the first pile. The sections below give each deadline and the 2026 limits, followed by one computed example. Each item has a longer article behind it if you need the mechanics.
What expires on December 31
- Charitable giftsA gift counts in the year it is paid. A credit card charge counts in the year you make the charge.
- EquipmentProperty must be ready and available for use in 2026 to be deducted for 2026.
- 401(k) deferrals$24,500 limit for 2026, plus $8,000 catch-up at age 50 or older. Deferrals come out of paychecks.
- Roth conversionsTaxed on the 2026 return if done in 2026, and a conversion can no longer be undone.
- Loss salesCapital losses offset gains plus $3,000. Mind the 30-day wash-sale window on both sides.
- Annual giftsThe first $19,000 per recipient in calendar 2026 stays out of taxable gifts.
- 17 daysOct 15: extended 2025 returns, last day for a 2025 SEP
- 254 daysDec 1: HSA last-month rule test date
- 384 daysDec 31: gifts, equipment, deferrals, conversions
- 499 daysJan 15, 2027: fourth estimated payment
- 5189 daysApr 15, 2027: 2026 IRA and HSA contributions
Most of the deductions people want sit at day 84, December 31. The IRA and HSA dates are 105 days later.
Retirement and HSA money that waits until spring
Two of the most useful year-end deposits are not year-end deadlines at all. A traditional or Roth IRA contribution for 2026 can be made any time until the 2026 return is due, which is April 15, 2027 for most people, and extensions do not stretch that date. The 2026 limit is $7,500, or $8,600 if you are 50 or older. An HSA works the same way: the deadline for a year is April 15 of the next year, and the 2026 limit is $4,400 for self-only coverage or $8,750 for family coverage.
SEP-IRA contributions for a self-employed person run on the longer clock. You can open the SEP and fund it as late as the due date of the return including extensions. If you extended your 2025 return, October 15, 2026 is the last day to fund a 2025 SEP.
A solo 401(k) is trickier. For contributions that count for the prior year, the plan generally has to have been established by the end of that year. There is one exception: since 2023 a sole proprietor with no employees can adopt a 401(k) after year end, as long as it is adopted by the filing deadline, extensions not counted. Because the details turn on your plan document, ask the plan provider before relying on it. The retirement deadlines article covers each plan type, and the HSA article covers eligibility.
One date to remember inside the HSA rules: the last-month rule tests whether you are eligible on December 1. That is the one HSA date that falls in the year, not after it. A new SIMPLE IRA plan is generally off the table for 2026 as well, because the start-date window closes October 1.
The deadline sorting table
| Move | Deadline | 2026 limit |
|---|---|---|
| 401(k) salary deferral | Through payroll, by December 31 | $24,500; $8,000 catch-up at 50+ |
| Charitable gift | Paid by December 31 | Itemizers: above 0.5% of AGI. Others: $1,000 ($2,000 joint) |
| Equipment for Section 179 or bonus | Placed in service by December 31 | $2,560,000 Section 179 limit |
| Roth conversion | Completed by December 31 | No dollar limit; taxed as income |
| Annual gift exclusion | Given by December 31 | $19,000 per recipient |
| IRA contribution | April 15, 2027, no extension | $7,500; $8,600 at 50+ |
| HSA contribution | April 15, 2027 | $4,400 self-only; $8,750 family |
| SEP-IRA contribution | Return due date, including extensions | Depends on compensation |
| Fourth estimated payment | January 15, 2027 | Safe harbor amount |
Charitable giving changed for 2026
A charitable gift is deductible for the year it is paid. A gift charged to a credit card is treated as made when you make the charge, so a card charge in late December counts for 2026 even if you pay the card bill in January.
Two new rules start in 2026. If you itemize, only the part of your total charitable giving above 0.5% of your adjusted gross income is deductible. At $200,000 of AGI that floor is $1,000, so the first $1,000 of gifts does nothing. If you take the standard deduction, which is $16,100 for a single filer and $32,200 for a married couple filing jointly in 2026, you can still deduct up to $1,000 of cash gifts, or $2,000 on a joint return.
The non-itemizer deduction is narrower than it sounds. It covers cash only, and not gifts to a donor-advised fund or to a supporting organization. If you are close to the line between itemizing and not, bunching two years of gifts into one may help. Keep every receipt, and see the substantiation article for what each size of gift requires.
Equipment: in service, not just bought
For 2026, a business can expense up to $2,560,000 of qualifying property under Section 179. The limit starts to shrink once the cost of such property placed in service during the year passes $4,090,000. Separately, 100% bonus depreciation is available again for qualified property acquired and placed in service after January 19, 2025.
The date that matters is when the property is placed in service, not when you sign the invoice. Property is in service when it is ready and available for its specific use, even if you are not using it yet. A machine delivered on December 28 but not installed until January is a 2027 asset. Section 179 is also limited to the taxable income from your businesses, so it cannot create a loss by itself. The choice between the two tools is covered in Section 179 versus bonus depreciation.
Buying something you do not need to catch a deduction rarely pays. A deduction returns only a fraction of the cost, and the cash is gone either way.
Estimated payments and withholding
The fourth installment for 2026 is due January 15, 2027. If you file your 2026 return by January 31, 2027 and pay the balance, you do not need to make that payment. You generally avoid the underpayment penalty by paying in at least 90% of your 2026 tax, or 100% of the tax on your 2025 return, rising to 110% if your 2025 AGI was over $150,000. The safe-harbor article works through the choices.
Withholding has a quirk that helps late in the year. Tax withheld from wages is treated as paid in equal parts on each estimated due date unless you prove the actual dates. Raising your withholding in the last paychecks of the year can therefore cover a shortfall from earlier quarters, which a late estimated payment cannot.
Example, hypothetical: three moves for a $200,000 earner
Take a single consultant with $200,000 of AGI who itemizes and sits in a 24% marginal bracket. This rate is an assumption for the example, so check your own bracket first. She is considering three moves:
First, a $40,000 piece of equipment placed in service on December 29. Second, $6,000 of cash gifts to public charities. Third, a $4,400 HSA contribution with self-only coverage, made in December.
The 0.5% floor on $200,000 is $1,000, so $5,000 of the $6,000 gift is deductible. Equipment at $40,000 saves $9,600 at 24%, the gift saves $1,200 and the HSA saves $1,056. The three deductions total $49,400 and the federal saving is $11,856. The equipment move accounts for most of the saving and the biggest outlay, so it deserves the most scrutiny. The HSA deposit could also wait until April 15, 2027 and still count for 2026.
| Tax saved | |
|---|---|
| Equipment, $40,000 | $9,600 |
| Charity, $5,000 net of floor | $1,200 |
| HSA, $4,400 | $1,056 |
Equipment dwarfs the others because the deduction is large, not because it is the best use of cash.
Computed: deduction x 24% assumed marginal rate, with a $1,000 charitable floor
Common mistakes
- Treating the December 31 and April 15 deadlines as the same, so an HSA or IRA contribution gets rushed or an equipment purchase gets delayed.
- Buying equipment in December that is not installed and operational until January.
- Forgetting that a Roth conversion cannot be recharacterized, so a bigger-than-planned conversion cannot be reversed.
- Selling a loser on December 20 and buying it back on December 28, which the wash-sale rule disallows.
- Counting on the old charitable rules: the 2026 floor means small gifts may produce no itemized deduction.
- Assuming extensions move a payment date. An extension changes when you file, not when you pay.
What to do, in order
This week
Pull a year-to-date estimate of your 2026 income and tax. Without it, none of the choices below can be sized.
By mid-October
If you extended your 2025 return, fund any 2025 SEP-IRA by October 15, 2026.
By November 15
Ask payroll how many pay periods remain, and adjust 401(k) deferrals and withholding to fit the $24,500 limit.
By December 1
Confirm HSA eligibility on that date and decide whether a Roth conversion is worth the added income.
By December 20
Order equipment so it is installed and usable by December 31, and make charitable gifts you want counted in 2026.
By December 31
Realize any harvest losses, finish gifts and make last-minute deposits that need to land in 2026.
By January 15, 2027
Make the fourth estimated payment, or plan to file by January 31 and pay the balance.
By April 15, 2027
Fund the IRA and HSA for 2026 if you have not already.
