Material requirements planning answers one question repeatedly: given what we owe customers, what do we need, and when do we need to act?
Netting and offsetting
Gross requirements come from demand exploded through the BOM. Net requirements subtract on-hand and scheduled receipts. The result is offset backwards by lead time to give a release date — the date action must start, not the date the material is needed.
Exception messages are the product
Mature planning operations spend their time on MRP's exception messages: expedite, defer, cancel and past-due. If your planners never work an exception list, the system is being used as a record keeper rather than a planning tool.
Lead times deserve real attention
Lead times entered once at implementation and never revisited are one of the most common causes of chronic shortages and excess. Review them against actual receipt history at least annually, and by supplier where volatility is high.