Income deferral
Delay invoicing late-December work until January. Hold off depositing checks received Dec 30-31 until Jan 1. Defer year-end bonuses or contract milestone payments until after January 1. Each delayed dollar of income is a delayed dollar of tax — generally good if you're in a higher bracket this year than next, or if cash flow is tight.
Expense acceleration
Prepay January expenses in late December: rent, insurance premiums, software subscriptions, contractor invoices. The 12-month rule lets cash-method taxpayers deduct prepaid expenses if the coverage period does not extend more than 12 months beyond the payment date.
Section 179 / bonus depreciation
Buy and place in service equipment by December 31 to claim Section 179 or bonus depreciation in the current year. "Place in service" means ready and available for use — not just ordered or delivered. Document the in-service date carefully.
Retirement contributions
SEP-IRA contributions can be made as late as the extended return due date (October 15) for the prior tax year. Solo 401(k) elective deferrals require the plan to be in place by year-end; employer profit-sharing contributions can wait until the extended return due date.
Charitable contributions
For sole proprietors, charitable contributions are personal (Schedule A) and require itemizing. For S-corps, charitable contributions pass through on K-1 and are itemized at the shareholder level. Bunching charitable contributions every other year — making two years' worth in one calendar year — can clear the standard deduction threshold and produce a meaningful tax saving.
Where the IRS publishes guidance on this topic
The IRS publishes a layered set of free resources on most small-business tax topics: a relevant publication (usually one of Pub 334, 463, 535, 587, 946, 560, or 583), the instructions to the relevant form, the "Small Business and Self-Employed Tax Center" landing pages on IRS.gov, and the Audit Techniques Guides written for IRS examiners. Reading the agency's own materials is the cheapest tax education available. They are written in plain English, updated annually, and they reflect exactly the framework an examiner will apply if your return is selected.