Available-to-Promise (ATP)

Available-to-Promise (ATP) is the calculated quantity of a product that can be reliably promised to a customer for a given date, derived from current stock plus planned incoming supply, minus quantities already committed to other orders. It answers the practical question asked during order entry: "Can we deliver this, and when?" ATP is a core function of order management in an ERP system and links sales commitments to actual supply and inventory. Reliable ATP prevents over-promising, reduces late deliveries and supports realistic dates in the order-to-cash process.

How ATP is calculated

At its simplest, ATP takes the projected supply, on-hand stock and scheduled receipts from production or purchasing, and subtracts the demand already committed to confirmed orders. The remaining quantity, time-phased by date, is what can be promised to new orders without breaking existing commitments. Because supply and demand are spread over time, ATP is usually expressed per period rather than as a single number, so a salesperson can see not just whether stock exists today but when additional quantities become available. The calculation depends on accurate inventory, order and lead-time data.

Variants and related concepts

• Capable-to-Promise (CTP): goes further by checking whether production capacity and materials could be arranged to meet a date, often using APS.
• Allocation-based ATP: reserves quantities for specific customers or channels before promising.
• Backward and forward scheduling: finding the latest start that meets a date, or the earliest date achievable from now.

ATP draws on the same supply picture produced by material planning and MRP, and interacts with policies such as safety stock that may be excluded from promisable quantities.

Why it matters in the order process

ATP turns inventory and supply data into a dependable delivery commitment at the moment of sale. Without it, organisations either promise dates they cannot meet, damaging customer trust, or hold excess stock to be safe, tying up capital. A working ATP function lets sales give realistic dates immediately, supports prioritisation when supply is scarce, and feeds accurate expectations into downstream fulfilment. In make-to-stock environments ATP is straightforward; in make-to-order or engineer-to-order settings, capable-to-promise logic and capacity checks become more important.

Practical considerations

The reliability of ATP rests on data quality: real-time or near-real-time stock figures, accurate lead times, and a clear definition of which supply counts as promisable. Decisions about whether safety stock, blocked stock or unconfirmed receipts are included materially change the result and should be defined deliberately. In distributed or multi-site operations, ATP must consider stock across locations and any inter-site transfers. When evaluating ERP systems, buyers should examine how ATP is calculated, whether it is time-phased, whether it extends to capable-to-promise, and how it behaves when supply and demand change after a promise has been made.

Related topics

• MRP — Material Requirements Planning
• APS — Advanced Planning and Scheduling
• Order-to-Cash
• Material Planning