What usually makes a monthly close run late?

Detailed Explanation

Two things dominate: manual reconciliations, and source data that arrives after the close has already started. Manual work does not scale with volume and cannot be parallelised past the number of people who know how to do it. Late source data is worse, because it makes every downstream task wait regardless of how efficient that task is. The first move is not automation — it is documenting where the time actually goes. Close timing only becomes predictable once the bottlenecks are written down rather than assumed.