MRP or advanced scheduling: planning with capacity assumed or capacity counted

Comparison criteria

Criteria are stated explicitly and neither option is declared a winner: which one fits depends on the constraint that binds hardest in your operation.

A scheduler is only as honest as the model of your plant

Finite scheduling produces a plausible-looking sequence from whatever it is told, which makes bad data more dangerous here than almost anywhere else. Run rates copied from an estimate rather than measured, routings that omit the deburring nobody documented, a resource calendar that ignores the planned maintenance window, setup times entered as a single average across dissimilar jobs — each of these produces a schedule the floor cannot achieve. Confidence then collapses quickly, because people compare the schedule with reality every single day. Validating the model against a few weeks of actual production before relying on it is the difference between adoption and an expensive unused module.

Time-phased planning fails quietly, which is why it survives

The weakness of assuming capacity is that nothing announces the problem. The plan is issued, the dates are impossible, and the gap is absorbed by overtime, expediting and a supervisor's judgement about which job matters. Because the plant delivers most of the time, the planning approach appears to work while a considerable amount of informal effort holds it together. Recognising this is the first step in the decision: measure how many orders are expedited, how often a plan is overridden, and how much overtime exists to recover dates. If those numbers are small, capacity is genuinely not your constraint.

Deciding what to schedule finitely and what to leave alone

Modelling an entire plant to the same depth is rarely worth it. The productive approach is to identify which resources genuinely constrain output and model those properly, while treating the rest with simpler assumptions. That keeps the maintenance burden proportionate and concentrates accuracy where it changes the answer. It also makes the model comprehensible, which matters because planners must be able to explain a schedule to a supervisor who disagrees with it. A model nobody can explain is abandoned within a few months, regardless of how sophisticated the underlying optimisation happens to be.

Frequently asked questions

Does finite scheduling replace time-phased material planning?

Generally not. Most implementations keep requirements planning for materials and purchasing, and schedule the production side against real capacity, with the two exchanging demand and supply information. Replacing material planning entirely means the scheduler must also handle purchasing horizons, supplier lead times and stock policy, which many are not designed to do well. Treating them as complementary — one deciding what is needed, the other deciding when it can realistically be made — is the more common arrangement.

What has to be true before scheduling software is worth attempting?

Routings that reflect what actually happens, run rates measured rather than estimated, a reliable feed of what has been completed, and someone with the authority and knowledge to own the model. Beyond the data, you need a plant where the schedule is genuinely followed; if supervisors are accustomed to sequencing by their own priorities, a scheduler produces a document that is ignored. The organisational readiness usually takes longer to establish than the technical implementation.

How do I know whether capacity or material is my real constraint?

Look at why jobs are late. If work sits waiting for parts, the constraint is supply and better sequencing changes little. If material is available and jobs queue at a particular resource, the constraint is capacity and sequencing becomes valuable. Most plants have both, varying by product and by period, so the useful measure is which cause accounts for most of your delay. Recording a reason code against every late order for a few weeks answers the question more reliably than opinion does.