Inventory management is a balancing act. Businesses must maintain enough stock to meet customer demand without tying up excessive capital in products that may take months to sell.
Yet, even established retailers, manufacturers, and distributors struggle to find this balance. Some accumulate excess inventory that requires discounting or additional storage, while others run out of essential products and risk losing sales.
The problem is rarely limited to purchasing too much or too little. Inventory levels reflect a chain of decisions involving demand forecasting, procurement, production planning, supplier lead times, and the quality of information available to decision-makers.
The financial implications can be substantial. In a May 2023 analysis, McKinsey & Company reported that US retailers held about $740 billion in unsold goods. The analysis linked the inventory glut to supply chain disruptions, precautionary overordering, and a subsequent shift in consumer spending.
This illustrates a central challenge: inventory decisions based on yesterday’s conditions can become costly when demand, supply, or customer preferences change.
Excess stock and stockouts may appear to be opposite problems, but both can arise from the same underlying weakness: a mismatch between inventory decisions and actual demand.
Excess inventory
Stock levels exceed what the business can reasonably sell or use within the required period. This increases storage and handling costs, ties up working capital, and exposes products to obsolescence, spoilage or markdowns.
Insufficient inventory
Available stock falls below actual demand. This can lead to missed sales, delayed production, incomplete orders, emergency replenishment, and reduced customer confidence.
The appropriate inventory level depends on the product, demand variability, supplier reliability, replenishment time, and desired service level. There is no single stock target that works equally well across every product category or business.
Demand forecasts guide purchasing, production and replenishment. When they fail to reflect actual market conditions, businesses risk ordering too much or too little stock.
Overestimating demand can lead to excess inventory, while underestimating it can cause stockouts. These errors often stem from relying on historical averages, overlooking seasonality or failing to account for changing customer preferences and promotions.
For example, a distributor expecting monthly sales of 5,000 units might purchase 6,500 units, only to sell 4,000. This leaves excess stock, while purchasing just 3,500 units against demand of 5,000 could create a shortfall.
Regular forecast updates, comparisons with actual sales, and scenario planning help businesses adjust inventory levels as demand changes.
Long or inconsistent supplier lead times make it difficult to align inventory with actual demand. Delays caused by manufacturing schedules, port congestion, or customs clearance can lead to stockouts. In response, businesses may place larger orders, creating excess inventory when supplies finally arrive.
A 2000 study by Chen, Drezner, Ryan and Simchi-Levi in Management Science examined how forecasting and lead times influence fluctuations in supply chain orders, highlighting the value of centralised demand information.
Businesses should therefore account for lead-time variability when setting reorder points and safety-stock levels, considering supplier reliability, demand uncertainty and the cost of potential shortages.
When sales, purchasing, warehouse operations, and finance rely on disconnected systems, inventory decisions often become inconsistent. Sales teams may overlook allocated stock, purchasing may miss goods in transit, and finance may identify excess inventory only after costs have increased.
A 2012 study by Robert Bray and Haim Mendelson, published in Management Science, analysed 4,689 publicly traded US companies from 1974 to 2008. It found that approximately two-thirds exhibited the bullwhip effect, where order fluctuations exceed changes in actual customer demand.
Without accurate, shared information, businesses risk making decisions based on distorted demand signals. Integrating stock levels, sales trends, purchase orders, and supplier deliveries helps identify potential shortages and excess inventory earlier.
Applying the same replenishment rules to every product can lead to inventory imbalances. Fast-moving items may need frequent replenishment and safety stock, while slow-moving or seasonal products require more selective purchasing.
Supplier constraints, such as minimum order quantities and bulk discounts, can also encourage businesses to buy more than they need, increasing holding costs and the risk of obsolescence.
The Association for Supply Chain Management (ASCM) distinguishes between cycle stock, which supports regular demand, and safety stock, which protects against uncertainty.
Businesses should tailor ordering policies to each product’s demand patterns, value, criticality and replenishment lead time rather than rely on a single approach.
Promotions, festivals, product launches and seasonal shifts can cause demand to fluctuate sharply. Outdated forecasts may lead businesses to miss sales opportunities or accumulate unsold stock.
For example, retailers may order extra inventory ahead of peak seasons, only to face weaker demand or delayed deliveries. McKinsey’s 2023 analysis of excess retail inventory highlighted how supply chain disruptions and changing consumer spending contributed to this problem.
Manufacturers and distributors face similar risks when demand changes after production or purchasing commitments are made. Businesses can reduce these risks by updating forecasts using sales trends, promotional calendars, and seasonal patterns, while considering staggered orders or flexible production schedules.
The bullwhip effect occurs when small changes in customer demand trigger increasingly larger order fluctuations across the supply chain. For example, a temporary sales increase may prompt a retailer to order extra stock, leading distributors and manufacturers to increase their own orders and production.
When demand returns to normal, businesses across the supply chain may be left with excess inventory.
A 1997 study by Hau Lee, V. Padmanabhan and Seungjin Whang, published in Management Science, identified demand forecasting, order batching, price fluctuations and rationing behaviour as key causes of this effect.
Sharing actual customer demand data, coordinating replenishment and avoiding excessive reactions to short-term changes can help reduce these fluctuations.
A business does not necessarily have too much or too little inventory across the board. It can experience both problems at the same time.
A distributor might hold months of supply of slow-moving products while frequently running out of high-demand items. A manufacturer may have surplus finished goods that customers do not need, yet lack a critical component required to fulfil urgent orders.
This situation often reflects an imbalance in the product mix, stock allocation or replenishment priorities rather than a simple shortage of total inventory.
The distinction matters because aggregate inventory figures can hide problems at the product level. A warehouse may appear well stocked overall even when essential items are unavailable. Conversely, a high total inventory value may include goods that are unlikely to sell at their intended price.
Businesses need to assess inventory by SKU, location, and demand category, with particular attention to:
These measures provide a more useful picture of inventory health than total stock value alone.
Reducing inventory imbalance requires more than increasing stock or cutting purchase orders. Businesses need a planning process that connects demand, supply, inventory and financial objectives.
A practical approach includes five priorities.
Planning systems can support this process by bringing demand forecasts, inventory projections, supply constraints and alternative scenarios together. Rather than reacting only after shortages or surpluses emerge, decision-makers can assess potential outcomes before committing to purchasing or production decisions.
Businesses end up with too much or too little stock when demand expectations, replenishment decisions and actual operating conditions fall out of alignment. Forecasting errors, uncertain lead times, fragmented information, inflexible ordering policies and supply chain disruptions can all contribute to the problem.
The answer is not to minimise inventory at every opportunity. Excessively lean stock can expose a business to supply disruptions, while excessive buffers can tie up capital and increase the risk of waste. The objective is to maintain inventory at levels that support customer demand and operational continuity without unnecessary cost.
Achieving that balance requires accurate and regularly updated demand information, product-specific inventory policies, coordinated supply chain decisions and continuous performance monitoring. With these capabilities in place, businesses can make more informed replenishment decisions, improve stock availability and use working capital more effectively.
