Build-to-Schedule

Build-to-schedule is the strict version of schedule adherence and the metric of choice when mix and sequence actually matter to the customer or the downstream operation. A shop that ships the right total but builds it in a convenient order may look fine by schedule adherence and be quietly causing problems for whoever consumes the output. BTS is the metric that catches it. It is harder to score well on than plain schedule adherence by design, and that strictness is its value.

"Hitting the volume is the easy half. Hitting the mix and the sequence is what the plan was actually for."

How build-to-schedule works

The calculation compares planned to actual at three levels and combines them into a single score. Most BTS calculations multiply the three percentages, which means a 90 percent score on any one factor drops the overall number meaningfully. The arithmetic is deliberate: BTS punishes partial wins.

The three factors

• Mix. The right ratio of variants. If the plan called for 60 percent product A and 40 percent product B and the line produced 80 percent A and 20 percent B, the mix is off even if the total volume is right.
• Volume. The right total quantity. The most familiar factor and the one schedule adherence focuses on.
• Sequence. The right order. Critical when downstream operations consume the output in sequence-dependent ways, like automotive assembly lines that build vehicles in a specific configuration order.

BTS is usually calculated as the product of the three percentages, which is mathematically strict. A line at 95 percent on each of mix, volume, and sequence has a BTS of about 86 percent, not 95. The compounding is intentional; it captures the reality that all three factors have to hold for the schedule to actually be met.

Where build-to-schedule fits on the shop floor

Imagine a 30-person automotive component shop running three product variants for a tier-one supplier. The customer's assembly line consumes parts in a sequence tied to the vehicles being built that shift. The customer's daily call-off specifies not just how many of each variant but the exact sequence the parts should arrive in.

The shop reports 96 percent schedule adherence and assumes that is enough. The customer's recent scorecard shows BTS at 78 percent. The customer's downstream line has been doing extra sorting at receipt to put the parts in the right order for their assembly, which is costing them about three labor hours a shift and creating tension with the shop's account team.

The diagnosis is that the shop has been hitting volume but reordering the sequence to minimize changeovers. From the shop's perspective, that looks like good lean thinking: minimize setup, maximize flow. From the customer's perspective, it has been creating a sorting problem. The fix is twofold. First, the shop accepts that sequence is a real constraint, not just a customer preference. Second, a quick-changeover project reduces setup time enough that following the sequence costs less than it used to. Six months later BTS climbs from 78 to 93. The customer's sorting effort disappears. The relationship improves. The metric did its job by making the cost of the shortcut visible.

Common mistakes with build-to-schedule

• Treating sequence as optional. When the customer or downstream operation depends on sequence, ignoring it on the BTS calculation hides a real failure that someone is paying for.
• Rolling up across long windows. A weekly or monthly BTS averages out the sequence misses. Daily BTS is the right cadence in most cases.
• Setting BTS as a target before the system can support it. A shop with hour-long changeovers cannot reasonably hit high BTS on a sequenced schedule. Improve setup time first, then tighten the metric.
• Confusing BTS with schedule adherence. They measure different things. A shop with strong schedule adherence and weak BTS is hitting volumes but breaking sequence.
• Reporting only the headline BTS score. The three factors carry different signals. Knowing which one is dragging the number tells you where to put improvement effort.

Build-to-schedule and related Lean tools

Build-to-schedule is the strictest cousin of schedule adherence and feeds directly into customer-facing on-time delivery. It is most achievable in operations that practice heijunka, the discipline of leveling production by volume and mix, and that have the changeover capability to run mixed-model production without significant setup losses between variants. BTS is a demanding metric, but in environments where it matters, no other metric captures the full requirement as cleanly.