Categorizing transactions means assigning each expense or income to the right account in your chart of accounts. This determines how your financial statements look, what deductions your accountant can claim, and whether you actually understand where your money goes.

The main categories are straightforward. Income covers everything you earn from products or services. Cost of goods sold includes direct costs tied to what you sell like materials or subcontractor labor. Operating expenses are the ongoing costs of running your business. Assets are purchases with lasting value like equipment or vehicles. Owner draws and contributions track money moving between you and the business.

Operating expenses are where most transactions land and where people get confused. Common subcategories include rent, utilities, insurance, professional services, office supplies, marketing, travel, meals, bank fees, and software. The specific categories you use should reflect how you want to see your spending grouped rather than matching some generic template.

The key is consistency. If you categorize something as “supplies” once, don’t call it “materials” next month. If you split advertising across “marketing” and “promotions” randomly, your reports become meaningless. Pick a category for each type of expense and use it every time. Monthly bookkeeping that includes proper categorization prevents the scramble at tax time and gives you financial reports you can actually use.

When you’re unsure about a transaction, think about what it’s for rather than what it looks like. A laptop isn’t “electronics” - it’s equipment or computer expense depending on your capitalization approach. A business dinner isn’t “restaurant” - it’s meals and entertainment. The IRS cares about the purpose, not the vendor name.

Common mistakes include mixing personal and business expenses, creating too many categories, using “miscellaneous” as a catch-all, and categorizing the same vendor differently each month. These habits make your financial reports unreliable and create extra work when tax season arrives.

Most San Diego business owners benefit from having a San Diego bookkeeper handle categorization because the rules matter and consistency requires attention. Someone who knows your industry will set up categories correctly from the start and catch issues before they become problems on your tax return.

If you’re handling your own books, review categorization monthly before transactions pile up. Look for anything marked “uncategorized” or “ask my accountant” and deal with it while you still remember what it was. Waiting until year-end means guessing at transactions you made eight months ago, which leads to errors and missed deductions.