Keep the three lead-time workflows separate
Manufacturing lead time adds pre-processing, active processing, and post-processing. Order lead time compares an order date with a delivery date or forecasts delivery from a stated interval. Supply-chain lead time adds supply delay and reorder delay. The inputs are conditional because these formulas answer different questions.
Manufacturing lead time includes more than cycle time
Manufacturing lead time equals pre-processing plus processing plus post-processing. Processing time is the cycle-time component only. Reporting its share of the total helps show whether waiting and handoff time or active production is the larger contributor.
Use elapsed calendar days for orders
A forecast adds the stated whole calendar-day interval to the order date; zero days returns the same date. Actual order lead time subtracts the order date from the delivery date, so July 1 to July 15 is 14 elapsed days. Weekends and holidays are included, and the order date is not counted as an extra day.
Supply-chain lead time adds two inventory delays
Supply-chain lead time equals supply delay plus reorder delay. The published example combines a 1-day supply delay with a 14-day reorder delay for a 15-day total. This simplified planning relationship does not model demand variability or safety stock.
Document the calendar and operational assumptions
Real delivery can depend on business-day calendars, cut-off times, time zones, supplier variability, queues, batching, transport, inspections, partial shipments, disruptions, and service-level rules. Treat the result as a transparent planning estimate and apply the organization's written convention for commitments.