Inventory types: how to analyse your stock by root cause and make better decisions

Inventory types only start to make sense when you look at stock by root cause. In reality, the issue is not how much inventory you hold. What matters is which decisions created it and what impact those decisions are having on the business.

Many organisations manage inventory as an aggregate: total value, days of cover or turns. That approach hides a critical reality. Stock is the outcome of multiple operational, commercial and financial decisions that have built up over time. Supplier MOQs, biased demand forecasts, inflated lead times or poorly planned campaigns can all sit inside the same number, making any rigorous analysis difficult.

For that reason, a traditional inventory classification adds limited value from a management perspective. The real question is not whether stock is cycle stock or safety stock. The focus should be on inventory by cause: what generated it, how much control you have over it and how it affects service, cost and working capital.

Making this shift is essential for any organisation that wants more precise decision-making. Once you understand where inventory comes from, you can act with judgement, prioritise properly and avoid local optimisations that end up damaging end-to-end supply chain performance.

Why you have too much stock

Most companies do not carry excess inventory for one single reason. It usually comes from multiple decisions compounding over time.

Supplier MOQs, optimistic forecasts, inflated lead times or poorly planned campaigns all create additional stock. The issue is that, when inventory is analysed as an aggregate, those causes get mixed together and visibility is lost.

Many organisations then try to fix the problem with generic actions: cutting cover, tweaking order quantities or putting pressure on procurement. Without understanding the root cause, however, these actions often create side effects such as stockouts or service deterioration.

In other words, excess inventory is not a volume problem. It is a diagnosis problem.

The mistake of managing it all the same way

One of the most common inventory management mistakes is treating all stock in the same way.

Applying the same policies to every product (the same cover targets, the same replenishment rules or the same review criteria) ignores operational reality. And that reality is simple: not all inventory follows the same logic.

Stock created by an MOQ should not be managed in the same way as safety stock. Equally, it makes little sense to treat a stable-demand item the same as a highly volatile one.

This one-size-fits-all approach usually leads to two issues. Some SKUs end up with excess inventory, while others run into stockouts. Most critically, both problems can exist at the same time.

So the first step towards efficient management is accepting that inventory is not a single thing. It is made up of different layers that behave differently.

Inventory types by root cause

To make better decisions, you need to break inventory down by what created it. This approach helps you understand which part of stock is structural, which is temporary and which is simply inefficient.

Lot-size stock

This type of inventory appears when purchasing or production decisions are driven by minimum lot sizes (MOQ) or local efficiency targets.

In these cases, the business buys or makes more than it needs in the short term, which increases stock levels. While it may make sense from a unit cost perspective, it often creates structural overstock if it is not managed properly.

Forecast-driven stock

Forecast-driven inventory is directly linked to the quality of demand planning.

When there is a positive bias, meaning demand is consistently overestimated, orders exceed what is actually needed. This stock is particularly risky because it looks “planned”, yet it is really hidden inefficiency.

Variability-driven stock

Uncertainty in demand or supply forces companies to hold safety stock.

In many cases, however, this inventory is oversized. That happens when variability is not measured properly or when static parameters are used that no longer reflect today’s reality.

Lead time-driven stock

Lead time is one of the strongest drivers of inventory. The longer the replenishment lead time, the more cover you need.

Issues arise when lead times are unreliable or padded for safety. That creates a knock-on effect that increases stock structurally.

Promotion-driven stock

Promotional and seasonal campaigns require demand to be anticipated, which means building inventory in advance.

If campaigns are not planned properly, excess stock after the campaign is common, especially when actual demand falls short of expectations.

Obsolete stock

Obsolete inventory relates to products that have lost demand or commercial relevance.

This type of stock is one of the biggest sources of inefficiency because it ties up capital and takes up space without creating value. It is also often the result of past decisions that were not reviewed in time.

What decision to take in each case

Once you have identified the causes behind inventory, the next step is deciding what to do in each situation. The goal is not to reduce stock indiscriminately. It is to act specifically on each type.

Reduce lot sizes

For lot-size stock, reviewing purchasing and production conditions is essential.

That may involve renegotiating supplier MOQs, adjusting order frequency or rethinking your manufacturing strategy. The aim is to reduce excess without sacrificing operational efficiency.

Fix the forecast

If the issue is coming from the forecast, improving demand planning quality is the priority.

That includes measuring and managing bias, separating baseline demand from promotions and building more robust consensus processes within S&OP.

Reset safety stock

For safety stock, recalculate levels based on real variability.

Rather than covering uncertainty with inventory alone, it also helps to work on the drivers: improve forecasting, reduce lead times or increase operational flexibility.

Take action with suppliers

Where lead time is the root cause, decisions should focus on supplier management.

Shortening lead times, improving reliability or diversifying supply (dual sourcing) are key levers to reduce the inventory required.

Plan promotions properly

For promotional stock, better planning is the lever.

Clear separation between promotional and baseline demand, volume adjustments and defined exit strategies are all critical to prevent residual overstock.

Remove stock

For obsolete inventory, the decision is straightforward: action is required.

That can mean clearance, targeted promotions or discontinuation. While margin may take a hit, doing nothing is usually more costly over time.

Where you are losing money

The biggest cost of inventory is not always obvious.

Beyond the stock value itself, there are hidden costs such as obsolescence, storage, operational complexity and service impact. Poorly managed inventory can even create excess and stockouts at the same time.

When the cause of stock is not understood, it is also common to take decisions that reduce inventory in the short term but worsen overall profitability.

That is why the real economic impact is not how much inventory you have, but what kind of inventory you are accumulating.

How to do it without spreadsheets (or chaos)

Many companies try to manage this complexity in spreadsheets. As the number of SKUs, locations and variables grows, however, spreadsheets stop being viable.

The main issue is not just calculation capacity. It is traceability and consistency. Keeping rules consistent, updating parameters in real time or simulating scenarios reliably becomes difficult.

That is why managing inventory by cause requires tools that can:

• Model different policies.
• Segment products.
• Support data-driven decisions.

Without that, the process becomes manual, slow and error-prone.

Real example: Tareca Vending

A clear example of this approach is the success story of Tareca Vending.

The company faced a common situation: high inventory levels combined with difficulty maintaining service. By analysing stock by root cause, they found that much of the problem was not total volume, but how inventory was distributed.

From there, they redefined replenishment policies, adjusted parameters and prioritised decisions based on the real impact of each inventory type.

The result was a significant improvement in the balance between inventory and service level, showing that the answer is not simply “reduce stock”, but manage it better.

Start managing your inventory by root cause

Taking this step does not mean transforming your entire planning model overnight. It does require a fundamental change in how you analyse inventory. Moving from an aggregated view focused on how much stock you hold to a structured view focused on why you hold it is what enables decisions with real impact.

Once you start breaking inventory down by cause, internal conversations change. Stock reduction stops being a generic goal and becomes a set of concrete levers: where to adjust purchasing policies, where to improve forecasting, where to act with suppliers or where to accept the issue is structural. Most importantly, you can prioritise based on real economic impact.

This approach improves operational efficiency and helps balance the three core supply chain dimensions: service, cost and capital. Optimising inventory is not about driving it to the minimum. It is about aligning it with business reality and constraints.

That is why relying on Excel alone is often not enough. As complexity increases (more SKUs, more locations, more variables), it becomes essential to have solutions that can model scenarios, segment properly and support more consistent decision-making.

This is where solutions like SCP Studio help structure the approach. By integrating demand, inventory and supply planning, they make it possible to analyse stock end to end, understand its causes and adjust policies continuously. It is not only about visibility. It is about turning that visibility into real operational decisions with impact on service, cost and capital. So if you want to apply this approach to your inventory management, request a free demo and we will show you how.