MRP systems and finite capacity scheduling, explained
A manufacturing resource planning system is usually the first serious software a growing plant buys. It is also where many plants discover that knowing what to buy is not the same as knowing when an order will ship. This page explains what MRP systems do, where they stop, and what fills the gap.
What a manufacturing resource planning system does
An MRP system keeps the product structure and the inventory in one place and calculates requirements from it.
- Bills of materials for every product, often several levels deep
- Inventory on hand, allocated and on order
- Purchase and work order suggestions with dates
- Costing, lot tracking and purchasing in the fuller suites
For purchasing and inventory control, this is exactly the right tool.
Where MRP systems for manufacturing stop
Most MRP systems plan with fixed lead times and infinite capacity. A work order gets a start date calculated backwards from its due date, as if the machine it needs were waiting for it. When five work orders need the same machine on the same day, the system shows five start dates on that day and no conflict.
- Lead times are fixed numbers, not a result of what is queued
- No sequence per machine, so no view of which job runs first
- Setup and changeover time rarely counted
- A breakdown does not move anything until someone edits dates by hand
That is why plants with a working MRP system still keep a scheduling spreadsheet next to it.
MRP system, finite capacity scheduling, or both
| Question | MRP system | Finite capacity scheduling |
|---|---|---|
| What do we need to buy? | Yes, its core job | Shortages per order and date |
| When does each job run, on which machine? | Rarely, lead times are fixed | Yes, operation by operation |
| Which orders will be late? | Only against fixed lead times | Yes, from the real queue on each machine |
| Where is the bottleneck? | Not shown | Named, with utilisation |
| What happens after a breakdown? | Dates edited by hand | Rest of the week rescheduled in one click |
Many plants need both halves. ProductionPlanning.ai covers the scheduling half, adds the shortage check on the Plant plan and above, and sits next to the MRP system or ERP you already have. Read more on MRP software and advanced planning and scheduling.
An MRP system for small business, or a schedule first
For a plant of twenty or forty people, a full MRP suite can be more than it needs on day one. If the daily pain is late orders and a spreadsheet that falls apart after every breakdown, a finite capacity schedule with shortage checks solves that first. See production scheduling software for small business.
See what the schedule adds to your MRP system
Run the demo on a real week of orders and compare the late order list with what your system shows today.
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