Start with a clear chart of accounts
Every transaction gets mapped to an account in your chart of accounts. Before you categorize anything, make sure that chart reflects how your business actually spends and earns money. Group accounts into the standard buckets: income, cost of goods sold, expenses, assets, liabilities, and equity.
Keep the expense list short enough to be usable but detailed enough to answer real questions. If you never look at a breakdown between two categories, merge them. If your accountant or tax form needs a line item separated, keep it its own account. Common expense accounts include rent, utilities, software subscriptions, meals, travel, advertising, contractor payments, and bank fees.
Resist the urge to create a new category for every unusual purchase. A bloated chart of accounts is harder to keep consistent, and inconsistency is what makes reports untrustworthy.
Categorize consistently, one transaction at a time
Work from your bank feed or an imported statement and assign each line to a single account. The goal is consistency: the same vendor and the same type of purchase should land in the same category every time. If you buy fuel from the same station, it should always be a vehicle or travel expense, not sometimes meals.
Read the transaction description, the amount, and the date together. A payment to a hardware store might be supplies, equipment, or a job-specific cost depending on context. When you are unsure, check the receipt or invoice rather than guessing. A note in the memo field will save you time when you revisit it later.
Set up rules for recurring transactions. Most bookkeeping tools let you tell the system that anything from a given payee goes to a specific account. Rules speed up routine work, but review them periodically because vendors change and a rule can quietly miscategorize a batch of entries.
Handle transfers, splits, and mixed transactions
Transfers between your own accounts are not income or expenses. Moving money from checking to savings, or paying down a credit card, should be recorded as a transfer or a liability payment, not a category on your profit and loss. Miscategorizing transfers inflates both income and expenses and throws off your reports.
Some transactions cover more than one category. A single office-supply order might include stamps, printer ink, and a chair. Use a split to divide the amount across the correct accounts so each report line stays accurate. Loan payments almost always need a split between principal, which reduces a liability, and interest, which is an expense.
Owner activity needs care too. Money the owner puts in is usually equity, and money the owner takes out is a draw or distribution, not payroll or an expense. Keep personal and business spending separated. If a personal charge slips onto the business account, record it as an owner draw rather than a business expense.
Review and reconcile before you close the month
Categorizing is not finished until you reconcile. Match your categorized transactions against the actual bank statement so the ending balance in your books equals the balance on the statement. Reconciliation catches missing transactions, duplicates, and amounts entered incorrectly.
Scan an uncategorized or 'ask my accountant' bucket at least monthly and clear it out. Anything parked there is a report waiting to be wrong. Also review your largest expense categories for outliers, a personal charge sitting in advertising or a refund recorded as income will stand out.
When you import statements from a PDF into a spreadsheet or accounting file, confirm the dates, amounts, and signs came through correctly before you categorize. Fixing an import error early is far faster than tracing it back after three months of reports depend on it.