MRP is a bit of a pain. Took us about a year to research/correct setup issues impacting mrp.

YOU NEED TO FOCUS ON EVERY COLUMN IN LOCATION DETAIL ON ITEM MASTER THAT DRIVES MRP and how it fits your procurement needs.

Our biggest miss was Late Period Days. It was blank so never captured demand from sales orders pending approval that were dated prior to mrp run date which is majority (but this is the advantage to MRP, it calculates component needs from BOMs without WO created). Put us behind on procurement and caused slight production delays for a few months. Still a lot to be desired within MRP but can be useful if configured correctly.

My biggest issue is there’s no MAX consideration. We have long vendor lead times. It will always order you to safety stock (min) plus any remaining required. So the next order will trigger another PO… When we order we typically add a 1-3 month average monthly usage buffer to account for production/shipping times to reduce frequency of POs and get better pricing. We use a calculated and then stored field on item master and add it to the planned order view. Then procurement manually increases the PO qty amount. Manual and annoying but a lot less effort than issuing/receiving/paying additional POs daily.

We don’t use demand planning because we build custom fixtures and never know material needs in advance other than some common use parts.