An aging report sorts open receivables into buckets, typically current, 1 to 30 days past due, 31 to 60, 61 to 90, and over 90. It shows which customers owe money, how much, and how late it is. Older balances are less likely to be collected, so the aging also informs bad-debt estimates.
For cash forecasting, aging is a starting point, not a forecast. Each customer's real payment behavior, plus contract terms such as retainage, should drive the expected receipt date. A thirteen-week cash outlook built on explicit collection assumptions is more reliable than one that assumes every invoice is paid on its due date.