The budget is derived from the previous year, but the money itself is not. It's not like they set up a savings account that ended on Dec 31 that they begin drawing from on Jan 1. Tracking cash flow is a job, and it goes from month to month and week to week. And business expenses count against your income in the current fiscal year, not the previous. Depreciation is also a thing, and it's why certain items would be paid for from different funds.