There are about 95 days left in 2026, and almost every tax-saving move that matters this year shares one feature: a hard December 31 deadline. Equipment must be placed in service, not merely ordered. Retirement plans must exist, not merely be intended. Charitable gifts must clear, estimates must be paid, and contractor paperwork must be collected while vendors still answer their email. Miss the date and the deduction waits a full year — or vanishes entirely.
This checklist distills year-end planning into the ten moves with the biggest after-tax payoff for small business owners, updated for the One Big Beautiful Bill Act (OBBBA) rules now in force for 2026. Work through them in October, not December, while there is still time to act on what you find.
1. Get Equipment Placed in Service by December 31
If you buy equipment this year, the write-off depends on when it goes to work — not when you sign the purchase order. Property must be acquired and placed in service by December 31, 2026 to generate a 2026 deduction.
The good news is that 2026 is the most generous equipment year in recent memory. The OBBBA permanently restored 100 percent bonus depreciation for qualified property acquired after January 19, 2025, and raised the Section 179 expensing limit to $2,560,000, with phase-out starting at $4,090,000 of equipment placed in service. For most small businesses, that means the full cost of machinery, vehicles, computers, and furniture bought and installed this year can be deducted this year.
Practical cautions: delivery slips kill deductions, so confirm lead times in writing for anything ordered in Q4. Listed property such as vehicles needs a mileage log to survive an audit. And if a purchase would create a loss you cannot use, consider whether spreading the deduction over future years beats bunching it into 2026.
2. Revisit Your SALT Strategy and PTE Election
The OBBBA raised the itemized state and local tax (SALT) deduction cap to $40,000 for 2026, with inflation adjustments and a scheduled reversion to $10,000 in 2030. If you live in a high-tax state, that higher cap changes the math — but for many pass-through owners, the bigger lever remains the state pass-through entity tax (PTE) election, which converts capped individual SALT into a fully deductible entity-level tax.
Q4 is decision time because PTE elections, estimated payments, and extension mechanics are state-specific and deadline-driven. Model the election against your projected K-1 income, your resident and nonresident filings, and the timing of the entity-level payments so the deduction lands in the right year. Owners who skip this review routinely leave five figures on the table in high-tax states.
3. True Up Withholding and Your Q4 Estimated Payment
Withholding tables and estimated payments set early in the year rarely match reality after OBBBA's new and expanded deductions. A few minutes of projection now prevents both an underpayment penalty and an interest-free loan to the Treasury.
Your fourth-quarter estimated payment is due January 15, 2027. To stay inside the federal safe harbors, aim to have paid at least 90 percent of this year's tax or 100 percent of last year's tax (110 percent if your adjusted gross income exceeds $150,000, or $75,000 if married filing separately). Pass-through owners with lumpy K-1 income should annualize rather than assume four equal quarters were enough. Also confirm your payroll system is capturing any new reporting categories your employees need for OBBBA-era deductions, such as qualified tips and overtime.
4. Max Out Retirement Contributions While the Window Is Open
Retirement funding is the rare deduction that pays you twice — once on this year's return and again in compounding. The 2026 limits give you meaningful room:
- 401(k) elective deferrals: $24,500, plus an $8,000 catch-up at age 50 and older, or an $11,250 catch-up for ages 60 through 63.
- Total annual additions: $72,000 per participant across employee and employer contributions.
- SEP IRA: up to 25 percent of compensation, capped at $72,000.
- SIMPLE IRA: $17,000 in salary reduction, plus catch-up contributions.
- Traditional and Roth IRAs: $7,500, plus a $1,100 catch-up at 50 and older.
Deadlines differ, and that is the trap. A Solo 401(k) must be established by December 31 for you to make 2026 elective deferrals, while a SEP IRA can be opened and funded as late as your filing deadline. Employers considering a new safe harbor 401(k) needed it effective by October 1, and existing safe harbor plans owe employees their annual notice by December 1. If any of those dates apply to you, calendar them this week.
5. Time Income and Deductions to Your Advantage
Cash-basis businesses control which year income and expenses land in, and December is when that control is worth the most. If 2026 was a high-income year, consider deferring year-end invoices into January while accelerating deductible spending into December: prepay January rent, stock up on supplies, pay outstanding vendor bills, and schedule equipment repairs before New Year's Eve.
Prepaid expenses are deductible this year under the 12-month rule as long as the benefit period does not extend more than a year past the payment date. Accrual-basis businesses have less flexibility but can still review year-end accruals for bonuses, warranty reserves, and other fixed liabilities. Match the timing to your marginal rate forecast — deferring income into a year when you expect higher rates can backfire.
6. Bunch Charitable Gifts to Beat the Standard Deduction
With the 2026 standard deduction at $32,200 for joint filers, $16,100 for single filers, and $24,150 for heads of household, most owners take the standard amount every year — which means routine annual giving produces zero tax benefit. Bunching fixes that: concentrate two or three years of donations into 2026 so itemized deductions clear the standard amount, then take the standard deduction in the off years.
A donor-advised fund makes bunching painless. You claim the full deduction in the contribution year while directing grants to charities over time, and donating appreciated stock instead of cash avoids capital gains tax on the appreciation. Coordinate large gifts with liquidity events and Roth conversions so all three land in the year your bracket makes them cheapest.
7. Harvest Losses, Manage Gains, and Consider a Roth Conversion
Capital gain and loss planning remains one of the highest-return exercises you can do before year-end. Review your portfolio for positions trading at a loss and harvest enough to offset realized gains, plus up to $3,000 of ordinary income ($1,500 if married filing separately). Watch the wash-sale rule: repurchasing the same or a substantially identical security within 30 days before or after the sale disallows the loss.
A lower-than-usual income year — common for owners who reinvested heavily or had a slow K-1 year — is also the ideal window for a partial Roth conversion. Model the conversion amount against your bracket headroom, the phaseouts for OBBBA-era deductions, and Medicare premium thresholds before executing. Conversions done in December still count for 2026, but custodian processing queues are longest then, so start early.
8. Top Up Your HSA and Spend Down Your FSA
Health account deadlines cut in opposite directions, which is why both belong on the same checklist line. Health Savings Account contributions for 2026 — $4,400 for self-only coverage or $8,750 for family coverage, plus a $1,000 catch-up at 55 and older — can be made until April 15, 2027, but funding now starts tax-free growth sooner. Confirm your high-deductible plan still qualifies and that payroll HSA salary reductions are on track.
Flexible Spending Accounts run the other way: most plans require you to spend the balance by December 31 or forfeit it beyond a small rollover allowance. Schedule the dental work, order the glasses, and stock the medicine cabinet before the balance evaporates.
9. Start 1099 Prep Now Under the New $2,000 Threshold
January's information-return crunch is avoidable if you do the groundwork in Q4. For 2026, the OBBBA raised the reporting threshold for Forms 1099-NEC and 1099-MISC from $600 to $2,000 per payee, with inflation adjustments beginning in 2027. That spares many small vendor relationships from reporting — but every contractor at or above $2,000 still needs a correct Taxpayer Identification Number on file, and the furnishing deadline is February 1, 2027 (moved from January 31, which falls on a Sunday).
Act now: collect missing Forms W-9 before final payments go out, verify vendor names and TINs against IRS records, confirm which payees are corporations exempt from reporting, and flag attorney payments, which keep their own $600 gross-proceeds rule. Clean vendor records in October mean penalty-free filing in January.
10. Review Your Entity Structure and Real Estate Cost Segregation
Businesses outgrow their entity choices. A Q4 review should confirm your structure — sole proprietorship, partnership, S corporation, or C corporation — still fits your income level, state footprint, financing needs, and exit plans under OBBBA-era rules, including the now-permanent 20 percent qualified business income deduction and the more generous Section 1202 exclusion for C corporation stock. S corporation owners should document that officer compensation remains reasonable relative to distributions.
If you placed real estate in service in 2025 or 2026, also evaluate a cost segregation study. Reclassifying building components into shorter-lived property accelerates depreciation dramatically, and a study performed now can still pull deductions back through a change in accounting method. Coordinate the study with your PTE posture and bonus depreciation position so the accelerated deductions land where they help most.
Keep Your Year-End Books Audit-Ready
Every move on this checklist rests on the same foundation: books clean enough to act on. You cannot time deductions you cannot see, defend a home-office or vehicle write-off without a log, or file February information returns from a shoebox of invoices. Reconcile your accounts monthly through year-end, keep equipment invoices with their placed-in-service dates, and track charitable gifts, mileage, and contractor payments in one ledger you trust.
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