What is Replenishment Planning?

Replenishment Planning is the supply chain discipline of calculating the precise quantity of inventory required to be ordered from suppliers or shipped to locations to maintain a target service level, balancing the risk of running out of stock against the cost of holding excess inventory.

While Allocation is a "Push" process (distributing a finite amount of stock, usually for fashion/seasonal items), Replenishment is a "Pull" process (reacting to demand to refill stock, usually for basics/consumables). It answers the fundamental question: "We sold 10 units of milk today. Should we order 10 more to replace them, or 15 because a holiday is coming, or 0 because we have too much already?"

The Core Mechanics: The "Sawtooth" Model

Replenishment Planning revolves around managing the "Inventory Position" over time.

• The Reorder Point (ROP): The specific inventory level that triggers a new order. Formula: (Daily Demand × Lead Time) + Safety Stock.
• Safety Stock: The "buffer" inventory kept to protect against uncertainty (e.g., the truck is late, or sales spike unexpectedly).
• Lead Time: The time gap between placing an order and receiving it. If it takes 14 days for a supplier to deliver, you must order before you run out, covering the demand for those 14 days.

Why It Matters: The "Goldilocks" Problem

Replenishment is the engine of the "Always-On" economy.

• Service Level (Availability): The primary goal. If you promise a 98% service level, the system calculates the inventory needed to ensure that for every 100 customers who walk in, 98 find the product on the shelf.
• Working Capital Efficiency: Inventory is cash sitting on a shelf. Effective replenishment minimizes "Days of Supply." If you can lower your safety stock by 10% without hurting availability, you free up millions in cash flow.
• Logistics Optimization: It isn't just about "how much." It is about "how to ship." Good replenishment rounds orders up to fill a truck or pallet, ensuring you don't pay to ship "air."

Strategic Approaches

1. Min/Max (Static): The old way. "When we get down to 5 units (Min), order enough to get back to 20 units (Max)." This fails when demand changes (e.g., seasonality).
2. Time-Phased (Dynamic): The modern way. "Forecast demand for the next 52 weeks and order exactly what is needed for each specific week." This aligns inventory with future peaks and valleys.
3. Multi-Echelon: The advanced way. It optimizes the network as a whole. It might hold 80% of the safety stock at the central Distribution Center (where it is cheaper to hold) and only trickle 20% down to the stores, relying on fast shipping to cover spikes.