What counts as supplies
Items that are consumed within a year or have a unit cost below the de minimis safe harbor threshold ($2,500 per item or invoice). Examples: printer paper, pens, ink cartridges, file folders, postage, small office tools, cleaning supplies for the office, calendar planners.
Supplies vs. equipment
Items with a useful life of more than one year and unit cost above the safe harbor must generally be capitalized and depreciated, although Section 179 or bonus depreciation can deduct the full cost in year one anyway. Office furniture, computers, monitors, and software are typical examples that fall into the equipment bucket.
De minimis safe harbor
Reg. 1.263(a)-1(f) lets you expense items costing $2,500 or less ($5,000 with audited financials) per invoice or item without capitalization. Make the annual election by attaching a statement to your timely-filed return; most software handles this automatically.
Where it goes
Schedule C line 22 ("Supplies"). Some prefer line 18 ("Office expense") for common office consumables, reserving line 22 for industry-specific supplies (medical supplies for a healthcare provider, art supplies for a designer). Either is acceptable.
Recordkeeping
Receipts under $75 are not strictly required by Section 274 (which applies to travel and entertainment), but supplies records make the deduction defensible. A monthly Amazon order summary or a single year-end download from the office supplier suffices.
Worked example with numbers
Consider a sole prop with $100,000 in gross receipts and $30,000 in legitimate Schedule C deductions, including this category. Each additional $1,000 of qualifying expense reduces Schedule C net profit by $1,000, which reduces self-employment tax by approximately $1,000 × 92.35% × 15.3% ≈ $141, and reduces income tax by $1,000 × marginal rate. At a 22% federal marginal rate, the combined federal tax savings on each additional $1,000 of legitimate deduction is roughly $361, and state savings sit on top of that. The math is why disciplined categorization throughout the year pays for itself.
Common mistakes that disallow the deduction
The recurring ways this deduction gets disallowed in examination cluster in four categories: (1) personal-use expenses bundled with business (the deduction is disallowed entirely or apportioned downward); (2) inadequate substantiation (no receipt, no invoice, no business-purpose note); (3) the wrong line on Schedule C (not fatal, but it weakens audit defense); and (4) double-counting with another line (for example, deducting an expense on Schedule C and also on Form 8829, or as a personal itemized deduction on Schedule A). The fix in every case is contemporaneous bookkeeping and a clean chart of accounts.