Understanding Backward Scheduling
In supply chain and order management, backward scheduling is a background function used to determine when materials must be ready to meet a specific delivery deadline. Rather than starting from the moment an order is placed and adding lead times (forward scheduling), this method begins with the required delivery date and subtracts the time necessary for each step of the fulfillment process [1].
The primary goal of this process is to calculate the product availability date. This is the critical milestone by which sufficient stock must be available in the plant to fulfill the confirmed customer delivery [1]. If the material is not available by this date, or if the calculated dates fall before the current order date, the requested delivery date cannot be confirmed, and the system must switch to forward scheduling to find the next possible delivery date [2].
The Backward Scheduling Workflow
To plan an order backward, the system uses predefined time elements stored in the logistics database. Each milestone is subtracted from the previous one in a sequential chain [1].
Step 1: Establish the Required Delivery Date
The process begins with the customer’s requested delivery date. This serves as the anchor point for all subsequent calculations.
Step 2: Calculate the Goods Issue Date
The system subtracts the transit time (the time required for the shipment to travel from the warehouse to the customer) from the required delivery date. The resulting date is the goods issue date—the moment the product must leave the facility [1].
Step 3: Determine the Loading Date
From the goods issue date, the system deducts the loading time. This accounts for the time needed to physically load the goods onto the transport vehicle [1].
Step 4: Calculate Parallel Logistics Milestones
Once the loading date is established, the system typically calculates two parallel paths to ensure all prerequisites are met:
- Transportation Planning: The system subtracts the transportation lead time from the loading date to establish the transportation planning date [1].
- Picking and Packing: The system subtracts the pick/pack time from the loading date to determine the product availability date [1].
Worked Example: Calculating an Order Timeline
Note: The following scenario uses illustrative numbers to demonstrate the backward scheduling logic.
Scenario: A customer requests a delivery of custom packaging materials on October 20th.
| Logistics Step | Lead Time (Illustrative) | Calculated Date |
|---|---|---|
| Required Delivery Date | – | October 20 |
| Transit Time | 3 Days | October 17 (Goods Issue Date) |
| Loading Time | 1 Day | October 16 (Loading Date) |
| Pick/Pack Time | 2 Days | October 14 (Product Availability Date) |
In this example, the material must be physically present and available in the warehouse by October 14th to guarantee the customer receives their order by October 20th.
Product Availability Checks
Once the product availability date is determined, the system performs a product availability check. This is a background function that compares the requirement (the sales order) against various elements that influence material quantity [1].
The check considers several factors to determine if the quantity can be confirmed for the calculated date:
- Current Stock: On-hand inventory available today.
- Incoming Supply: Purchase orders, purchase requisitions, and planned production.
- Existing Commitments: Other sales orders and deliveries that have already reserved stock.
If the check is successful, the quantity is reserved, making it unavailable for other requirements, and a confirmation is generated [1].
Common Planning Constraints
Backward scheduling is highly efficient but is limited by real-world constraints. A requested delivery date cannot be confirmed if:
- Past Dates: Any of the calculated milestones (such as the product availability date) fall on a date before the order was actually created [2].
- Stock Shortages: The material is not available in the required quantity by the calculated product availability date [2].
- Capacity Limits: The warehouse or transportation provider cannot accommodate the volume on the calculated dates.
When these constraints are met, the system typically triggers forward scheduling, which calculates the earliest possible delivery date by adding lead times to the current date [2].
FAQ
What happens if the product availability date is in the past?
If the calculated product availability date occurs before the date the order was created, the requested delivery date cannot be confirmed. The system will then attempt forward scheduling to determine the next possible delivery date.
What elements influence the product availability check?
The check compares requirements against stock, existing sales orders, deliveries, purchase orders, and purchase requisitions to determine available quantities.