What Is a Due Anchor in Backward Scheduling?

A due anchor is the terminal deadline that a backward-scheduled job's last operation must end by: the engine right-aligns every step of the job against this anchor, working in reverse so the final step lands at or before it, with the anchor derived from the due date and the product's end-item lead time. It is the fixed point a just-in-time plan hangs from, the way a wedding cake is scheduled backward from the reception hour so it arrives fresh rather than four days early.

This entry is part of the EDGEBIC by User Solutions glossary; the broader dictionary lives in the manufacturing glossary.

Why Backward Scheduling Needs an Anchor

Backward scheduling is the just-in-time discipline: instead of starting a job as early as possible and letting slack pile up at the end, the engine places the job so it finishes just in time, with the slack sitting deliberately in front. To do that, it needs a single fixed deadline to align the last step against and then work backward from. That deadline is the due anchor.

Get the anchor wrong and the whole job shifts. Set it a day too early and the plan starts needlessly sooner; set it a day too late and the job misses its promise. So the anchor is computed carefully from two things: how the due date is stored, and how long the finished part takes to reach the customer.

How the Anchor Is Computed

Two adjustments turn a due date into a usable anchor.

First, the time-of-day rule. A due date entered with no time means finish by the end of that day, so the engine sets the anchor to the following midnight, giving the job the full working day. A due date that carries a specific time is honored exactly as entered. This avoids the classic off-by-a-day error where a date-only deadline is read as its opening midnight and a full working day silently vanishes.

Second, the end-item lead time. The product's delivery, cure, or ship tail after the last operation is subtracted from the due date. If the part needs 2 calendar days of freight, manufacturing must finish 2 days before the due date so the tail lands the part on the customer's dock exactly on time.

A Concrete Example

A customer order is due Friday, entered as a date with no time. The product carries a 2-day end-item lead time for shipping.

The engine first reads the date-only due date as "end of Friday," so the raw anchor is the midnight at the end of Friday. Then it subtracts the 2-day lead-time tail, moving the manufacturing deadline to the end of Wednesday. That Wednesday deadline is the due anchor. The engine right-aligns the job's last operation to finish by then, schedules the earlier steps backward from it, and the 2 days of freight carry the finished part to Friday. If the part had no lead time, the anchor would simply be end-of-day Friday.

How EDGEBIC Uses It

In EDGEBIC, the due anchor is the terminal deadline of a backward pass. When a new job is set to schedule backward, the engine builds the anchor from the due date (next midnight for a date-only value, exact for a timed one) minus the product's end-item lead time, then places the steps in reverse order, each right-aligned to a deadline derived from its successors, so the last step ends at or before the anchor.

Backward scheduling only applies to new jobs with a real due date; a job that has already started reschedules forward from its resume point instead. And if the backward pass cannot fit between the job's floor and its anchor, the whole job rolls back and schedules forward instead, which makes it a backward-infeasible job. For the full mechanism and how direction is chosen, see the backward scheduling overview.