Master production schedule (MPS)
A master production schedule (MPS) states which finished products a plant will build, in what quantities, in which time periods, typically weekly buckets over several months. It translates the aggregate S&OP plan into specific buildable items and is the direct input that material requirements planning explodes into component orders. A stable MPS is the foundation of stable supplier schedules.
Examples
Disaggregating the plan: S&OP commits 12,000 power tools for Q2 at family level. The MPS turns that into weekly builds: 450 of the 18V model, 300 of the 12V, and 175 of the brushless premium, about 925 a week across 13 weeks, sequenced around a planned line changeover in week 7.
Holding the fence: A distributor asks to double next week's order inside the 3-week frozen zone. The scheduler offers the full quantity in week 5, or half next week by pulling stock from another order plus a premium-freight top-up. The fence held, and the cost of breaking it was made visible instead of silently absorbed.
Definition
The MPS sits between two worlds. Above it, S&OP agrees on volumes by product family and month; below it, MRP needs exact items, quantities, and weeks to compute component orders. The master scheduler disaggregates one into the other, deciding which configurations to build and when, while consuming the forecast with actual customer orders as they arrive.
A schedule nobody can build is fiction, so each draft is checked with rough-cut capacity planning against bottleneck resources before release.
Stability is the master scheduler's real product. Time fences formalize it: a frozen zone (often 2 to 4 weeks) where the schedule changes only by exception, a slushy zone where substitutions within capacity are allowed, and a liquid zone where the forecast rules. Every change inside the fence cascades through MRP into supplier reschedules and expedites, which is why good plants measure schedule attainment and treat frozen-zone changes as priced decisions, not favors.