Repair vs improvement
A "repair" maintains the asset in efficient operating condition without materially adding to its value or prolonging its useful life. An "improvement" creates new functionality, extends useful life, or adapts the asset to a new use — improvements must be capitalized and depreciated.
Tangible property regulations
Reg. 1.263(a)-3 created the BAR test (Betterment, Adaptation, Restoration) to distinguish capital improvements from repairs. Most routine maintenance — replacing burned-out HVAC components, patching a roof leak, repainting an office — is repair. Replacing the entire HVAC unit, the entire roof, or the building structure is improvement.
Routine maintenance safe harbor
Reg. 1.263(a)-3(i) provides a safe harbor for "routine maintenance" you reasonably expect to perform more than once during the asset's class life. Routine activity that meets the safe harbor is currently deductible without further analysis.
Small taxpayer safe harbor for buildings
Taxpayers with average annual gross receipts of $10 million or less may elect a safe harbor for buildings with unadjusted basis of $1 million or less. The safe harbor permits expensing of repairs, maintenance, and improvements up to the lesser of 2% of the building's basis or $10,000 per year.
Where it goes
Schedule C line 21 ("Repairs and maintenance"). Improvements that must be capitalized go on Form 4562.
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.