What is the difference between a budget and expense tracking?

Detailed Explanation

A budget is forward-looking: a plan that allocates income across necessities, savings and discretionary spending before the month starts. Expense tracking is backward-looking: a record of what actually happened. It exists to test the plan, not to replace it. You need both, and they only work together if the categories match. Tracking with a different category set than the budget produces two sets of numbers that cannot be compared, which is the usual reason people conclude that budgeting "does not work" for them.