Most revenues are received, and most expenses are spent, during the year to which they belong. However, in the early days of this year, you might still be collecting some of last year’s money (e.g. grant holdbacks and other receivables), and paying some of last year’s bills. In the later days of this year, you might start to receive or spend money in preparation for next season. And you’ll probably find that some of this year’s transactions just can’t be settled till the early days of next year.
Besides these timing issues, cashflow involves tax transactions that are not part of your revenues and expenses. For instance, everywhere in Canada we pay GST or HST (depending on your province) on the purchase of goods and services. Cash flows out to pay the sales tax – but for most organizations it’s partly or fully recoverable. Only the non-recoverable part is an expense.
The budget document doesn’t care about the timing of cash payments: it is based on the idea of accrual accounting, where revenues and expenses are “accrued” to the year where they belong, and the actual exchange of money might happen either earlier or later.
The cashflow document is all about the timing of cash, without respect to which year various things belong.