Inventory planning: deciding what stock is for

Decompose the total before arguing about it

Cycle stock exists because we order in batches rather than continuously. Safety stock exists because demand and supply both vary. Pre-build or seasonal stock exists because capacity is level and demand is not. Pipeline stock exists because goods take time to arrive and are already owned. Obsolete and blocked stock exists because something went wrong. These behave differently, respond to different levers, and should never be managed with one blanket target.

Policy is set per segment, not per company

A fast, predictable, high-value item and a slow, erratic, low-value one deserve different treatment even in the same warehouse. Segmenting by value contribution and by demand behaviour lets you concentrate availability effort where a stockout is expensive and to accept longer replenishment cycles where it is not. A single service target applied across a whole catalogue overserves the tail and underserves the items that pay the bills.

Targets have to be expressed in something operations can act on

A financial value target cannot be executed by a planner; a coverage target expressed in days or weeks of forward demand can. Translating the working capital envelope into per-item parameters — order quantities, reorder triggers, buffer levels — is the step most often skipped, which is why a board decision to reduce stock so frequently produces cuts in the wrong items and a service failure a few months later.

Reviewing the parameters, not just the outcome

Parameters decay. Lead times drift, demand patterns change shape, items mature and slow down. A planning process that reviews only stock outcomes will keep discovering symptoms; one that reviews parameter freshness — when each item's buffer and trigger were last recalculated against current behaviour — catches the cause. Where a system recalculates automatically, the review shifts to whether the inputs it is fed remain trustworthy.

Frequently asked questions

Is lower inventory always better?

No. Inventory buys availability, production stability and protection against supply variability. The objective is to hold the smallest amount that delivers the service and stability the business has decided to pay for, which is a different target from the smallest amount possible.

Who should own the stock target?

Supply chain typically owns the parameters and finance owns the funding envelope, with commercial owning the service commitment those parameters serve. Problems arise when one party sets a total without agreeing which of the three levers moves to accommodate it.

Why does stock rise even when sales are flat?

Common causes are order quantities set for old volumes, lead times that have lengthened without the buffer being revisited, receipts arriving in larger batches than consumption, and slow-moving lines that nobody has retired. Decomposing the total shows which of these is responsible.