What is the difference between ATP and CTP?

Available-to-promise (ATP) promises against the master schedule: finished goods on hand plus production already scheduled, whatever is not yet committed to other orders. Capable-to-promise goes further and checks whether the material and open capacity exist to build the order at all, so it can promise beyond what the schedule already planned. ATP promises against the plan; CTP promises against the plant's real ability to change the plan.

How is CTP different from checking stock?

A stock check only asks whether the finished product is in the warehouse now and says no if it is not, even when the line could easily build the rest by the due date. CTP treats unbuilt product as promiseable, provided it can prove the plant has the parts and the machine hours to make it in the window. It looks forward at what the plant can create, not backward at what already exists.

When should a plant use capable-to-promise?

CTP is most useful in make-to-order and assemble-to-order plants that routinely promise dates on product they have not built yet. If you mostly ship from stock, a stock check or ATP may be enough. If customers ask for quantities and dates that require building, and you want promises the floor can actually keep, CTP is the discipline that makes those promises honest.

Why do CTP promises sometimes turn out wrong?

Almost always because the data underneath is stale. If on-hand material is really an old spreadsheet estimate, or the open capacity a check sees ignores a machine that just went down, CTP will promise a date the plant cannot hit. The promising logic is fine; the gap is between the model and the floor, so keeping material and capacity data current is what makes CTP reliable.

Does CTP replace the master production schedule?

No. CTP works alongside the master production schedule, not instead of it. ATP is calculated directly from the master schedule, and CTP extends promising beyond the schedule by checking real material and capacity for a specific order. A good master schedule is still what keeps the plant's overall plan coherent; CTP is the fast, order-level check layered on top of it.

What Is Capable-to-Promise (CTP)?

Q: What is capable-to-promise (CTP)?

Capable-to-promise is an order-promising method that checks in real time whether a plant can actually make and deliver an order by the requested date, testing both material availability and open production capacity, not just whether finished goods are already in stock. It lets a plant confidently promise product it has not built yet, because it has verified the components and the machine time to build it.

Q: What does a CTP check look at?

Two things at once, and both must pass: material, meaning the components and raw materials are on hand or arriving in time, and capacity, meaning there is uncommitted machine time, tooling, and labor on the right work centers to build the order by the requested date. If material is short, CTP dates the promise to material arrival; if capacity is short, it dates it to the first open slot.

How capable-to-promise checks real material and capacity to promise a delivery date on product you have not built yet, and how it differs from a stock check and from available-to-promise.

Capable-to-promise (CTP) is an order-promising method that checks, in real time, whether a plant can actually make and deliver a new order by the requested date, testing both material availability and production capacity, not just whether finished goods are already in stock.

When a customer asks "can you have 5,000 units by the 20th?", most order-entry systems answer by looking in the warehouse. If the stock is there, they promise it; if not, they either say no or guess. Capable-to-promise is the smarter answer. It looks past the shelf and asks whether the plant, given its materials, machines, and open schedule, can genuinely produce and ship the order on time. This post defines CTP, contrasts it with a simple stock check and with available-to-promise, and shows what it takes to run it honestly. It is educational, not vendor advice, and names no products.

What is capable-to-promise (CTP)?

Capable-to-promise is a customer-order promising technique that determines the earliest date an order can be delivered by checking both material availability and the available production capacity to make it, rather than only checking existing inventory. Where a stock check looks backward at what already exists, CTP looks forward at what the plant can create. It effectively runs a fast, focused capacity and material check for the specific order on the table and returns a date the plant can actually stand behind.

The word doing the work is capable. A promise based on stock says "we have it." A promise based on capability says "even though we do not have it, here is when we can make it, because we checked the components and the open machine time and both line up." That distinction is the whole point: it lets a plant confidently promise product it has not built yet, and refuse or re-date an order it genuinely cannot make in time, instead of promising blind and disappointing the customer later.

Each method looks a layer deeper. A stock check sees only what exists; ATP adds what is already scheduled; CTP checks whether the materials and machine time to build the order exist at all.

How is CTP different from a simple stock check?

A simple stock check answers only one question, is the finished product sitting in the warehouse right now, and promises the order only if the answer is yes. It is fast and it is honest about what it knows, but it is blind to everything the plant could make. Ask a stock check for 5,000 units when 3,000 are on hand and it says no, even if the line could easily produce the other 2,000 by the due date. CTP fills that gap by treating unbuilt product as promiseable, provided the plant proves it has the parts and the machine hours to build it in the window.

This is also where CTP separates from available-to-promise logic. Available-to-promise (ATP) is a step up from a raw stock check: it looks at finished goods on hand plus production already scheduled in the master schedule, and offers whatever of that is not yet committed to other orders. But ATP still assumes the scheduled production will happen; it does not test whether adding this new order is physically possible. CTP goes the extra step, checking that the specific materials and the specific open capacity exist to make this order, so it can promise beyond what the master schedule already planned. Put simply: ATP promises against the plan, CTP promises against the plant's real ability to change the plan. The cost of that extra step is speed and data: a CTP check does more work than an ATP lookup, and it only pays off when the material and capacity numbers it reads are current, which is why plants that promise blind usually stop at ATP and plants that promise well invest in keeping the deeper picture live.

What does CTP actually check?

CTP runs two tests at once for the order in question, and both have to pass. The first is material: are the components, raw materials, and sub-assemblies either on hand or arriving in time to build the order? The second is capacity: is there enough uncommitted machine time, tooling, and labor on the right work centers, in the right window, to convert those materials into finished goods by the requested date? Only when both clear does CTP return a promise. If material is short, it dates the promise to when material arrives; if capacity is the binding limit, it dates the promise to the first open slot. This is the same finite-capacity thinking behind good capacity planning aimed at a single order in real time.

A short example makes the two gates concrete. A customer wants 5,000 units by the 20th. The warehouse holds 3,000, so ATP covers 3,000 and 2,000 must be built. CTP explodes the bill of materials for those 2,000, finds that the key component is on hand but the assembly line has only enough open time for 1,400 units before the 20th, and the rest not until the 23rd. A stock check would have flatly said no. ATP would have promised only the 3,000 already scheduled. CTP returns the honest, useful answer: 4,400 by the 20th, the full 5,000 by the 23rd. That granularity, splitting a promise by what material and capacity truly allow, is exactly what lets a salesperson give a customer a date the floor can keep, and it is why make-to-order plants treat CTP as the backbone of order entry rather than a nicety.

Both gates must pass for the requested date. If either fails, CTP does not just say no; it returns the realistic date the constraint allows.

How do you run a CTP check?

A capable-to-promise check follows a consistent sequence, whether a planner runs it by hand for one big order or a system runs it in a second for every quote:

Take the order and the requested date. Capture the product, quantity, and the date the customer is asking for.
Check finished goods and ATP first. If on-hand stock or already-scheduled production can cover it, promise from there; there is no need to build.
Explode the bill of materials for the shortfall. For the quantity that must be built, determine the components and raw materials required using the bill of materials.
Test material availability. Confirm each component is on hand or arriving, via purchase orders or production, before the build would need it.
Test capacity against the open schedule. Check that the required work centers have uncommitted time, tooling, and labor in the window, without breaking promises already made.
Return the earliest feasible date. Give the requested date if both gates pass, or the date set by the binding constraint if one does not.
Reserve or re-check on acceptance. When the customer accepts, hold the material and capacity so the promise is not quietly consumed by the next order.

What do the standards and data say?

Context from standards bodies and primary sources:

The order-promising family, available-to-promise and capable-to-promise, is defined in the planning body of knowledge maintained by the Association for Supply Chain Management (ASCM/APICS) which distinguishes ATP (based on the master schedule) from CTP (based on material and capacity availability).
ASCM's CPIM exam content manual places order promising, ATP, and capacity checking inside master planning and detailed scheduling, the same discipline that produces a realistic delivery commitment.
The difference matters at scale: the Bureau of Labor Statistics counts roughly 13 million manufacturing jobs in the United States, and make-to-order and assemble-to-order plants, where CTP is most useful, promise dates on unbuilt product every day.

The practical point: a promise is only as good as the material and capacity data behind it, so CTP is less an algorithm than a discipline of keeping those two pictures current.

Where CTP lives or dies: the data underneath

Capable-to-promise is only as trustworthy as the two pictures it checks. If on-hand material is really an estimate from a spreadsheet last touched Tuesday, or if the open capacity a check sees ignores the machine that went down an hour ago, CTP will confidently promise a date the plant cannot hit, which is worse than a cautious stock check because the customer believed it. The failure is rarely the promising logic; it is the gap between the model and the floor. Harmony is an AI-native layer that connects machines, software, and paperwork into one operational layer, with no rip-and-replace, so the inputs a promise depends on, real material on hand, real machine status, real remaining capacity on each line, become one current record instead of several stale ones. AI search returns cited answers across those records, so a planner weighing a rush order can ask what capacity is truly open on a line this week or whether a component has actually arrived and get a real answer before promising. It is the same paper-to-digital move Harmony makes elsewhere in the plant (see the CLS case study), and Harmony's digital workflows keep the promise connected to what the floor is actually doing. It also links naturally to the discipline of a solid master production schedule and to make-to-stock versus make-to-order decisions, since CTP is what lets a plant safely promise the make-to-order half.