End-of-Year Tax Planning for Small Business Owners: What to Do Before December 31

Most small business owners think about taxes in April. The ones who pay less tax think about it in October, November, and December — when there's still time to do something.

Tax planning after December 31 is tax compliance. Tax planning before December 31 is tax reduction. The window is what matters.

The Fundamental Levers

End-of-year tax planning for a business owner operates on two basic mechanisms:

Shift income later or deductions earlier: Taxable income = revenue minus deductions. If you can legally defer income to the next tax year or accelerate deductions into the current year, you reduce this year's taxable income. A dollar of income deferred from December to January buys 12–16 months before that dollar is taxed.

Change the character of what you owe: Some income is taxed at ordinary rates (the highest marginal rates); some at capital gains rates (lower, for long-term qualifying assets). Some deductions reduce ordinary income; others don't. Structuring transactions to maximize favorable rate treatment is character planning.

Specific Actions Worth Reviewing Before Year-End

Review your estimated tax payments. Have you paid 100% of last year's tax liability across four quarterly installments (or 110% if your prior-year AGI exceeded $150,000)? If not, the Q4 estimated payment (due January 15) gives you one more shot to catch up and avoid underpayment penalties. Calculate your expected annual liability and compare it to what you've paid. The shortfall is your Q4 payment target.

Equipment and asset purchases. Under the OBBBA-restored 100% bonus depreciation rules, qualifying property placed in service before December 31 can be fully deducted in this tax year. If you've been planning a major equipment, software, or asset purchase, completing it before year-end changes the deduction from future years to this year. "Placed in service" is the relevant date — the asset must be operational, not just ordered or delivered.

Retirement contributions.

• SEP-IRA contributions can be made until your tax return filing deadline (including extensions) — so this is one of the later-closing windows, but you need to have the account established.
• Solo 401(k) employee elective deferrals must be made by December 31 of the tax year. The employer contribution portion can be made until the return filing deadline.
• SIMPLE IRA employee contributions must be made before December 31.
• Review your year's income and calculate maximum contribution opportunities. Retirement contributions reduce taxable income dollar-for-dollar and are among the most powerful tax reduction levers available to small business owners.

Timing of year-end invoicing. If you're on cash-basis accounting (which most small businesses use), income is recognized when received, not when invoiced. Deciding whether to send December invoices or to wait until January changes when that income appears on your return. If you expect your rate to be the same or lower next year, deferring December billings you haven't sent yet may defer the associated tax.

Vendor and expense payments. Cash-basis taxpayers can accelerate deductions by paying expenses in December that they'd otherwise pay in January. Prepaying January rent, a software subscription, or an anticipated operating expense in December pulls that deduction into the current tax year. IRS rules generally allow prepayment deductions for expenses with benefit periods of 12 months or less (the "12-month rule").

Business structure review. Have you evaluated whether your current entity structure is still optimal? Year-end is a natural time for this — after a year of operating, your income levels and business trajectory are more certain. If you've had a significantly higher income year than expected, or if you're planning a major transaction next year, the structure question is worth revisiting with your attorney and CPA now rather than after the year closes.

S-corp salary review. If you're operating as an S-corp, payroll must be run before December 31 for W-2 income to be reflected in the current year. If you've been deferring your salary and plan to take a lump sum as W-2 compensation to bring your salary to a reasonable level, that payroll must be completed before year-end.

The Meeting You Should Schedule in October or November

The most effective end-of-year tax planning happens through a proactive conversation with your CPA in October or early November — not through a December 30 phone call.

By October, you have approximately 10 months of actual financial data. Your CPA can project your full-year income, identify the most impactful planning opportunities, and advise on specific actions before there's time pressure.

By December 15, you can execute most strategies and still have time to confirm they're completed before year-end.

By December 30, you're scrambling and some options have already closed.

The proactive call to your CPA should ask: What's my projected tax liability based on what we know? What are the highest-leverage actions available before year-end? What decisions need to be made in the next 30–60 days?

The Question Every Business Owner Should Ask in Q4

At some point between October and December, ask your CPA: "Is there anything I should do before year-end that I'm not doing?"

If your CPA can't give you an answer, that's either because your planning is already optimized (possible) or because they don't have enough visibility into your situation to identify opportunities (worth investigating).

This article is educational and does not constitute legal or tax advice. Tax planning strategies depend on individual circumstances, income levels, and entity structure. Engage a qualified CPA for guidance on your specific situation.