Annual cap and phase-out
The Section 179 deduction is limited to an annual dollar amount (over $1 million, indexed) and phases out dollar-for-dollar above an investment threshold (over $3 million, indexed). Few small businesses approach the phase-out, but it can affect those acquiring substantial equipment in a single year.
Eligible property
Tangible personal property (equipment, machinery, furniture, computers, off-the-shelf software, certain vehicles) used more than 50% in your trade or business qualifies. Most real property does not, with limited exceptions for qualified improvement property, roofs, HVAC, fire protection, alarm systems, and security systems on commercial property.
Taxable income limit
Section 179 cannot exceed your aggregate active trade-or-business taxable income — including W-2 wages from one job and self-employment income from another. Excess Section 179 carries over to future years and is deductible when business income is sufficient.
Section 179 vs bonus depreciation
Both let you front-load depreciation. Section 179 is elective and requires positive business income; bonus depreciation is automatic (with election out available class-by-class) and can create a loss. Most planners use Section 179 first to fine-tune to a target income, then layer in bonus depreciation for the rest.
Recapture
If business use of Section 179 property drops below 50%, you must recapture (add to income) the excess of the Section 179 deduction over the depreciation that would have been allowed under straight-line MACRS. Track personal use carefully on listed property to avoid surprise recapture income.
Where this fits in the larger Schedule C picture
Schedule C has more than two dozen named expense lines plus an "Other expenses" catch-all. For most small businesses, four or five lines drive the bulk of the deduction total — vehicle, home office, depreciation, contract labor or wages, and supplies — and the remaining lines individually contribute small amounts that nevertheless add up. Treating each named line as a recurring decision rather than an afterthought, and revisiting the categories each January, often surfaces $2,000–$5,000 in additional legitimate deductions that a less disciplined process would have missed entirely.
Documentation that survives an exam
An IRS examination of this deduction will request three things: proof of payment (bank or card statement), proof of the underlying transaction (invoice or receipt), and proof of business purpose (a contemporaneous note or calendar entry). The first two are usually trivial to produce; the third is where most filers fall short. Capturing business purpose at the moment of the expense — a one-line note in your bookkeeping software or a category and memo on the receipt-capture app — converts a generic charge into a documented deduction that will withstand scrutiny three to six years later when memory has faded.