What a Job That Will Not Fit Tells You Before You Promise

A due date the shop cannot make is worth finding at the moment you are deciding, not at the moment you are explaining. That sentence sounds obvious and is almost never what happens. In most plants the discovery arrives weeks later, after the order is entered, after upstream steps have eaten capacity, and after somebody has already told a customer a number.

EDGEBIC by User Solutions moves that discovery earlier for one specific class of job, and does it in a way that leaves the database untouched while you think. This post covers the mechanism, the arithmetic on a worked case, what the gate is actually worth, and the several places it does not apply. It sits under the EDGEBIC results guide.

The job that cannot fit is not an error

Backward scheduling is opt-in per order. You set the direction to Backward, give the job a due date, and the engine works right to left: it places the last operation so the job ends on or before the due date, then the one before it, and so on, as late as it safely can. The cut-off date is the floor, meaning do not start before this.

Sometimes there is not enough room between the floor and the due date for the routing's hours in sequence. Three things can cause it: the due date minus the product's lead time already sits at or before the cut-off, a step would have to start before the cut-off, or the capacity between the two dates simply is not enough.

What happens next is the design decision that matters. The engine does not fail the job and it does not leave a partial plan behind. The backward attempt is abandoned completely, and the whole order is scheduled forward instead. Backward never errors out where forward would have worked, so you always end up with a readable plan. The plan just happens to be late, and the engine says by how much.

The gate, and what is still unwritten while it is open

There is one setting behind this, in Options, on the Schedule tab, under When a Backward Job Doesn't Fit:

• Accept the forward schedule is the default. The fallback is taken silently and the run saves immediately. You find the lateness afterward, in the Days Late column.
• Show a popup so I can review it holds the run instead.

With the second option on, a screen headed Backward Schedule, Jobs That Don't Fit lists every affected job with its due date, start date, priority, the forward window the engine computed, and a red pill reading how many days late. Three buttons sit at the bottom:

That last row is the load-bearing one. Until you press a button, no schedule rows exist. No capacity has been claimed. Nothing has been communicated. You are holding a proposal, which is a materially different object from a commitment, and the difference is the whole return on this feature.

The arithmetic on a documented case

Take a real routing. Job JOB-2026-0129, Bracket-B, 50 pieces, direction Backward. Cut-off date Thursday July 16, which is today. Routing is Saw-1 for 2 hours, then CNC-Mill-1 for 8 hours. The product carries a 1 day lead time tail. Day Shift runs Monday to Friday, 08:00 to 16:00, and there is no other load.

With a due date of Wednesday July 22, the job fits comfortably and right-aligns against the date.

Now the customer wants it Friday July 17 instead. Machining would have to finish by the end of Thursday July 16, because of the one-day tail between the last operation and the due date. Between the cut-off at Thursday 00:00 and that limit there is exactly one 8-hour shift. The routing needs 10 sequential hours. Ten does not fit into eight.

The backward attempt is abandoned. The forward fallback runs: Saw Thursday 08:00 to 10:00, Mill Thursday 10:00 to 16:00 and Friday 08:00 to 10:00. Work ends Friday at 10:00, the job end lands Saturday July 18, and the pill reads 1 day(s) late.

One day. That is a number you can take to a customer while the order is still a conversation. Ask for Monday July 20 and the job is comfortable. Ask for Friday and you are choosing to be a day late with your eyes open, which is a legitimate business decision and an entirely different thing from an accident.

Where the money is, and how to size it yourself

The saving here is not in the schedule. It is in the difference between two versions of the same conversation.

Version one happens in week six. The order exists, material is staged, three upstream operations have run, and the customer is asking for a status update. Your options are overtime, an expedite that displaces other work, a subcontract at short notice, or a late delivery with whatever that costs in your contract. Every one of those is priced at emergency rates, and the customer's trust takes the hit regardless of which you pick.

Version two happens before the order is saved. Your options are a different due date, a different priority, a different start floor, or a polite decline. All four are free.

To size this in your own plant, count last quarter's late deliveries and sort them by one question: on the day the date was agreed, was there enough capacity between the earliest possible start and the promised date to run the routing in sequence? The jobs where the honest answer is no were never execution failures. Multiply that count by your average recovery cost, whatever combination of premium freight, overtime, and credit that actually is for you, and you have the annual figure this gate is competing for. Most plants find the number larger than they expected, because recovery costs are spread across several budgets and never totaled.

What the gate does not cover

It applies only to new backward jobs during a scheduling run. Four honest limits follow from that.

Forward jobs get nothing. A forward order starts where you tell it and ends where it ends. If that end is past the due date, you learn it from the Late Jobs report after the run, not from a gate before it.

Reschedules do not trigger it. Jobs already on the calendar continue forward when they are replanned, by the new-jobs-only rule. The gate is for the moment a job enters the plan.

The default is silent. Out of the box the setting accepts the forward fallback without asking. If nobody has changed it, no popup has ever appeared, and lateness is being recorded rather than reviewed. Check the Days Late column after runs, or switch the setting.

It cannot stop a promise made outside the system. If sales can commit a date without a scheduling run behind it, impossible dates keep arriving and the gate never sees them. This is a process decision, not a software feature, and it is the same gate every finite scheduler needs a human to close.

One more boundary worth stating plainly: a schedule is not a reservation. Simulating or scheduling a job does not hold capacity against anyone else, so two dates promised from the same picture can both look safe and cannot both be kept. That is covered in why a quoted date can move.

Why this is a scheduling problem and not a discipline problem

The reason unrealistic dates survive review in most plants is not carelessness. It is that the check is genuinely hard to do in your head. It requires knowing the routing's sequential hours, the capacity between two specific dates on specific machines, the lead time tail, and everything else already booked in that window. Nobody does that reliably at the speed order entry runs at.

A finite capacity engine does it in the time it takes to press a button, and User Solutions has been building engines that do it since 1991. The gate simply insists that the answer is read before the commitment rather than after it. For more on the direction rules underneath, see backward scheduling explained, and for the broader economics of dates nobody checked, see the cost of an unrealistic due date.

The takeaway

A backward job that will not fit produces a forward plan, a days-late number, and a decision point where nothing has been saved yet. Turn the popup on, keep cut-off dates at today unless material genuinely forces otherwise, and treat every red pill as a customer conversation you get to have early. Bring a handful of jobs you delivered late last quarter to a walkthrough of EDGEBIC and we will run each one against the capacity you had on the day you promised it.