What Is an ATP Horizon in Planning?

An ATP horizon is the forward date range across which available-to-promise is computed and quoted to customers. It is the boundary of the projection: inside it, every planning bucket has an opening balance, netted demand, planned supply, and a resulting availability figure that a salesperson can quote. Outside it, there are no buckets and therefore no calculated answer. EDGEBIC by User Solutions uses the horizon to keep promising honest, because a delivery commitment should end where the plan's knowledge ends rather than trailing off into optimism.

How it works

Available-to-promise is not a single number. It is a running calculation performed period by period. The projection starts from an opening balance, subtracts the demand landing in each bucket, adds the supply arriving in that bucket, and carries the resulting balance forward into the next one. Whatever is left uncommitted in a bucket is what can still be promised for a date in that bucket.

That calculation needs buckets to run in, and buckets only exist inside the horizon. The horizon therefore does two jobs at once. It sets how far ahead the projection will build periods, and it sets the last date for which a promise is a calculation rather than a hope. A shop with an eight-week horizon can answer "can we ship in six weeks" from data. It cannot answer "can we ship in fourteen weeks" the same way, because week fourteen has no bucket.

The bucket size matters alongside the length. A daily bucket gives fine-grained promising over a short range, which suits fast-moving stocked items. Weekly buckets suit a normal build plan, and a longer custom period suits slower planning cycles. The horizon is the outer edge; the bucket is the resolution inside it. Together they decide how precisely and how far ahead a promise can be made.

There is a temptation to set the horizon very long on the theory that more visibility is always better. It is not. Past the point where firm orders and forecasts exist, the buckets are empty of demand, so the projection shows large uncommitted availability. That availability looks reassuring and means very little, because the demand that will eventually fill those buckets has not been entered yet. A horizon that reaches well past your real demand visibility produces confident numbers with nothing behind them.

A concrete example

Think of a restaurant taking bookings. The host has a reservation book that runs eight weeks ahead. Each page is a day, and each day shows the tables already committed and the tables still free. Somebody calling for next Thursday gets a real answer, because that page exists and shows three tables still open. Somebody calling for a date six months out gets a different kind of answer, because there is no page for it. The host might say yes in principle, but that is a courtesy, not a booking backed by a count.

The reservation book's length is the horizon. The page for each day is the bucket. The tables still free on a page is available-to-promise for that day. Extending the book to twelve months does not create more tables. It just creates a lot of blank pages that all look wide open, so every request in month nine appears easy to accept, right up until reality fills those pages in.

Translated to a plant: a product with 200 units on hand, a build of 150 completing in week three, and committed orders of 80, 120, and 60 across the first three weeks has a real, computable promise position in each of those weeks. Week thirty, with no orders entered and no builds planned, shows a large notional availability that reflects nothing but an empty calendar.

How EDGEBIC uses it

The horizon governs how far forward the inventory projection is built, and every promise column a planner or salesperson reads is bounded by it. The bucket-by-bucket balance the horizon contains is the glossary term projected available balance, and the promise figure computed on top of that balance is available-to-promise. Reading the two promise columns correctly is covered in ATP discrete vs cumulative.

Because the horizon and the bucket size work together, it is worth setting them deliberately rather than accepting whatever is in place. The period grouping itself is explained in what is a planning bucket, and using the resulting numbers to answer a live customer question is walked through in how available-to-promise answers a sales question. The wider projection screen is covered in projected available balance explained.

The ATP horizon is the plan's stated limit of knowledge. Respecting it is what separates a promise from a guess. For the wider vocabulary, see the manufacturing glossary, and to see promising computed against a live plan, explore EDGEBIC.