Available-to-Promise (ATP) — Manufacturing Glossary

Available-to-Promise (ATP) is the uncommitted portion of a manufacturer's current inventory and planned production that can be promised to new customer orders. ATP gives sales teams a real-time answer to the question every customer asks: "When can you deliver?" — without over-committing resources that are already allocated to existing orders.

At User Solutions we see ATP as the critical link between the sales office and the shop floor. Manufacturers with accurate ATP stop over-promising and under-delivering, which is the fastest path to customer retention.

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How ATP Works

ATP is calculated from the Master Production Schedule (MPS) and existing customer order commitments:

ATP Calculation Method

Period 1 (current): ATP = On-Hand Inventory + MPS Quantity - Total Customer Orders booked before next MPS arrival

Subsequent periods: ATP = MPS Quantity - Customer Orders committed against that period's MPS

ATP quantities carry forward — uncommitted production in Week 3 remains available for orders due in Week 5.

Key Principle

ATP never double-counts. Each unit of inventory or planned production is committed to at most one customer order. Once an order consumes ATP, that quantity is no longer available for future promises.

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ATP Example

A manufacturer produces industrial valves. Current data:

• On-hand inventory: 50 units
• Safety stock: 10 units (not available for promising)

Week 1 ATP: 50 (on-hand) - 10 (safety stock) - 30 (committed) = 10 units

Week 2 ATP: 100 (MPS) - 60 (committed) = 40 units

Week 3 ATP: No MPS, no uncommitted inventory = 0 units (but Week 2 ATP carries forward, so 40 could cover Week 3 needs)

Week 4 ATP: 100 (MPS) - 35 (committed) = 65 units

Scenario: A new customer calls requesting 45 valves by Week 3.

The sales representative checks ATP:

• Week 1 ATP: 10 (not enough)
• Week 1 + Week 2 cumulative ATP: 10 + 40 = 50 (enough for 45)

The rep can promise delivery of 45 valves by Week 2 (or early Week 3 with shipping). The system immediately reduces Week 2 ATP from 40 to 5 so the next inquiry gets an accurate picture.

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Why ATP Matters for Scheduling

Prevents over-promising. Without ATP, sales teams estimate delivery dates based on intuition or outdated information. ATP provides a real-time, data-driven answer that accounts for existing commitments.

Connects sales to production. ATP links customer promises directly to the MPS, which feeds MRP and ultimately the shop floor schedule. When a sales rep consumes ATP, the commitment is visible to planning.

Reduces schedule disruptions. When every customer order is backed by ATP, planners are not surprised by orders that were promised without checking capacity. The schedule stays intact, and on-time delivery improves.

Works with scheduling software. Tools like Resource Manager DB provide the capacity visibility that supports ATP accuracy. If the MPS is capacity-validated through finite scheduling, ATP commitments are trustworthy.

Supports capable-to-promise (CTP) decisions. When ATP is insufficient, CTP logic can evaluate whether additional production capacity exists to accept the order — elevating ATP from a simple inventory check to a dynamic capability assessment.

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Related Terms

• Capable-to-Promise (CTP) — An advanced method that evaluates whether additional capacity and materials exist to promise orders beyond ATP.
• Independent Demand — Customer demand that ATP manages, ensuring uncommitted supply is accurately tracked.
• Safety Stock — Buffer inventory typically excluded from ATP to maintain a minimum floor.

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FAQ

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This term is part of the Manufacturing Glossary. For a deep dive into material planning, see our MRP Guide.