What business expenses are actually deductible?

The statutory standard is that an expense must be both ordinary, meaning common and accepted in your line of work, and necessary, meaning helpful and appropriate for the business. That is a broader test than people assume and covers most genuine costs of operating: software, professional services, business insurance, advertising, supplies, contractor payments, professional development, industry publications, and business travel. It is also narrower than the folklore suggests, because the expense must actually serve the business rather than merely being paid from the business account.

The categories with specific rules are where mistakes cluster. The home office deduction requires a space used regularly and exclusively for business, and exclusively means the room is not also the guest bedroom; it is available to self-employed people but was eliminated for employees. Business meals are generally 50 percent deductible and require a business purpose and, in practice, a record of who was present and why. Vehicle use requires either the standard mileage rate or actual expenses, tracked contemporaneously, and commuting from home to a regular workplace is never deductible. Clothing is deductible only if it is unsuitable for ordinary wear, which excludes the suit you bought for client meetings.

The framing that matters most is what a deduction is worth. It reduces taxable income rather than tax owed, so a 1,000 dollar deductible purchase saves you 1,000 multiplied by your marginal rate, perhaps 220 to 350 dollars for many filers once self-employment tax is included. Spending money you did not need to spend in order to save tax is a losing trade, which is worth remembering every December when the advice to buy equipment before year-end circulates. Keep contemporaneous records, because reconstructed documentation is what fails in an audit, and a bank statement showing an amount is weaker evidence than a receipt showing what it was for.