Inventory overstocking can harm both financial stability and operational efficiency. When an organization is overstocked, it ties up capital in excess inventory that might not sell, increasing storage costs and the risk of inventory obsolescence. Additionally, the funds used to purchase the excess inventory could have been better invested in other areas of the business, such as marketing or research and development. Overstocking also hampers cash flow, as money is locked in stock rather than available for immediate operational needs. Managing inventory effectively is critical for maintaining a healthy balance sheet and ensuring that resources are optimally allocated. Here is an in-depth exploration of the main causes of overstocking, their implications, and possible solutions.

1 Inaccurate Demand Forecasting

One of the primary causes of overstocking is inaccurate demand forecasting. When businesses rely on outdated forecasting methods or insufficient data, they can easily overestimate demand, leading to overstocking. A prime example is the clothing industry, where fashion trends can change rapidly. A well-known fashion brand recently faced challenges after overestimating demand for a new clothing line based on flawed data analysis, leading to unsold inventory.

To address this issue, companies can implement new technologies that automatically select the best forecasting methods for the data, incorporating trends and seasonal patterns to ensure accuracy. By improving forecasting accuracy, businesses can better align their inventory with actual demand, leading to more precise inventory management and fewer overstock scenarios. For instance, a Hardware retailer using Smart Demand Planner reduced forecasting errors by 15%, demonstrating the potential for significant improvement in inventory management​​​​.

2 Improper Inventory Management

Effective inventory management is fundamental to prevent overstocking. Without accurate systems to track inventory levels, businesses might order excess stock and incur higher expenses. This issue often stems from reliance on spreadsheets or inefficient ERP systems that lack real-time data integration.

State-of-the-art technologies provide real-time visibility into inventory levels, allowing businesses to automate and optimize reordering processes.  A large electric utility company faced challenges in maintaining service parts availability without overstocking, managing over 250,000 part numbers across a diverse network of power generation and distribution facilities. The company replaced its outdated system with Smart IP&O and integrated it in real-time with their Enterprise Asset Management (EAM) system. Smart IP&O enabled the utility to use “what-if” scenarios, creating digital twins of alternate stocking policies and simulating performance across key performance indicators, such as inventory value, service levels, fill rates, and shortage costs. This allowed the utility to make targeted adjustments to their stocking parameters, which were then deployed to their EAM system, driving optimal replenishments of spare parts.

The outcome was significant: a $9 million reduction in inventory, freeing up cash and valuable warehouse space while sustaining target service levels of over 99%​

3 Overly Optimistic Sales Projections

Businesses, especially those in growth phases, may predict higher sales than they achieve, leading to excess inventory intended to meet anticipated demand that never materializes. An example of this is the recent case with an electric vehicle manufacturer that projected high sales for its truck but faced production delays and lower-than-expected demand, resulting in an overstock of components and parts. This miscalculation led to increased storage costs and strained financial resources.

Another automotive aftermarket company struggled to forecast intermittently demanded parts accurately, frequently resulting in overstocking and stockouts.  Using AI-driven technology enabled the company to significantly reduce backorders and lost sales, with fill rates improving from 93% to 96% within just three months. By leveraging Smart IP&O forecasting technologies, the company could generate accurate estimates of cumulative demand over lead times, providing better visibility of potential demand scenarios. This allowed for optimized inventory levels, reducing storage costs and improving financial efficiency by aligning inventory with actual demand​.

4 Bulk Purchasing Discounts

The appeal of cost savings from bulk purchases can prompt businesses to buy more than needed, tying up capital and storage space. This often leads to storage challenges when excess stock is ordered to secure a discount.

To address this challenge, businesses should weigh the benefits of bulk discounts against the costs of holding excess inventory. Next-generation technology can help identify the most cost-effective purchasing strategy by balancing immediate savings with long-term storage costs. By implementing Smart IP&O, MNR could accurately forecast inventory requirements and optimize its inventory management processes. This led to an 8% reduction in parts inventory, reaching a high customer service level of 98.7% and reducing inventory growth for new equipment from a projected 10% to only 6%.

5 Seasonal Demand Fluctuations

Difficulty in aligning inventory with seasonal demand can result in surplus stock once the peak sales period ends. Toy manufacturers, for example, might produce too many holiday-themed toys only to face low demand after the holidays. The fashion industry frequently experiences similar challenges, with certain styles becoming obsolete as seasons change. The latest technologies can help businesses anticipate seasonal demand shifts and adjust inventory levels accordingly. By analyzing past sales data and predicting future trends, businesses can better prepare for seasonal fluctuations, minimize overstocking risk, and improve inventory turnover.

6 Supplier Lead Time Variability

Unreliable supplier lead times can lead to overstocking as a buffer against delays. If lead times improve or demand decreases unexpectedly, businesses may have excess inventory. For example, an auto parts distributor might stockpile components to mitigate supplier delays, only to find lead times improving suddenly.

Advanced technology can help by providing real-time data and predictive analytics to manage lead time variability better. These tools allow companies to dynamically adjust their orders, reducing the need for excessive safety stock.

7 Inadequate Inventory Policies

Outdated or incorrect inventory policies, such as faulty Min/Max settings, can lead to over-ordering.  However, using Modern technology to regularly review and update inventory policies ensures they align with current business needs and market conditions. By keeping policies up-to-date, businesses can reduce the risk of overstocking due to procedural errors. A recent case study demonstrated how a major retailer used Smart IP&O to revise inventory policies, resulting in a 15% reduction in overstock​​.

8 Promotions and Marketing Campaigns

Misalignment between marketing efforts and actual customer demand can cause businesses to overestimate the impact of promotions, resulting in unsold inventory. For example, a cosmetics company might overproduce a limited edition product, expecting high demand that doesn’t materialize. Leveraging Smart IP&O can help align marketing initiatives with realistic demand expectations, avoiding excess stock. By integrating marketing plans with demand forecasts, businesses can optimize their promotional strategies to better match actual customer interest.

9 Fear of Stockouts

Companies often maintain higher inventory levels to avoid stockouts, which can lead to lost sales and unhappy customers. This fear can drive businesses to overstock as a safety net, especially in industries where customer satisfaction and retention are crucial. A notable example comes from a large retail chain that significantly increased its inventory of household goods to avoid stockouts. While this strategy initially helped meet customer demand, it later resulted in excess inventory as consumer purchasing patterns stabilized. This overstocking contributed to a profit drop of nearly 90% in the second quarter, largely due to markdowns and the clearing of excess stock.

To mitigate such situations, businesses can utilize advanced inventory planning and optimization tools to provide accurate demand forecasts. For instance, a leading electronics manufacturer used Smart IP&O solution to reduce inventory levels by 20% without impacting service levels, effectively reducing costs while maintaining customer satisfaction by ensuring they had the right amount of stock on hand​​​​.

10 Overcompensation for Supply Chain Issues

Businesses may overstock to safeguard against ongoing supply chain disruptions, but this can lead to storage issues. For instance, a tech company might stockpile components to avoid potential supply chain hiccups, resulting in surplus inventory and increased costs. Advanced systems can help businesses better anticipate and respond to supply chain challenges, balancing the need for safety stock with the risk of overstocking. A technology firm used Smart IP&O to streamline its inventory strategy, reducing excess stock by 20% while maintaining supply chain resilience​​.

11 Long Lead Times and Unreliable Suppliers

Prolonged lead times and unreliable suppliers can lead businesses to order more stock than needed to cover potential supply gaps. However, less critical Items that are forecasted to achieve very high service levels represent opportunities to reduce inventory.  By targeting lower service levels on less critical items, inventory will be “right size” over time to the new equilibrium, decreasing holding costs and the value of inventory on hand. A major public transit system reduced inventory by more than $4,000,000 while improving service levels using our cutting-edge technology.

12 Lack of Real-Time Inventory Visibility

Without real-time insights into inventory, businesses often order more stock than necessary, leading to inefficiencies and increased costs. Smart IP&O enabled Seneca companies to model demand at each stocking location and, using service level-driven planning, determine how much to stock to achieve the service level we require.  By running and comparing different scenarios, they can easily define and update optimal stocking policies for each tech support rep and stockrooms.

The software has provided field technicians with evidence they did not have before, showing them their actual consumption, frequency of part use, and rationale for stocking policies, using 90% as the targeted service level norm.  Field technicians have embraced its use, with significant results:  “Zero Turns” inventory has dropped from $400K to under $100K, “First Fix Rate” exceeds 90%, and total inventory investment has decreased by more than 25%, from $11 million to $ 8 million.

In conclusion, overstocking seriously threatens business profitability and efficiency, leading to increased storage costs, tied-up capital, and potential obsolescence of goods. These issues can strain resources and limit a company’s ability to respond to market changes. However, overstocking can be effectively managed by understanding its causes, such as inaccurate demand forecasting, prolonged lead times, and unreliable suppliers. Implementing robust AI-driven solutions like Smart IP&O can help businesses optimize inventory levels, reduce excess stock, and enhance operational efficiency. By leveraging advanced forecasting and inventory optimization tools, companies can find the right balance in meeting customer demand and minimizing inventory-related costs.

You may remember the story of Goldilocks from your long-ago youth. Sometimes the porridge was too hot, sometimes it was too cold, but just once it was just right. Now that we are adults, we can translate that fairy tale into a professional principle for inventory planning: There can be too little or too much inventory, and there is some Goldilocks level that is “just right.” This blog is about finding that sweet spot.

To illustrate our supply chain fable, consider this example. Imagine that you sell service parts to keep your customers systems up and running. You offer a particular service part that costs you $100 to make but sells for a 20% markup. You can make $20 on each unit you sell, but you don’t get to keep the whole $20 because of the inventory operating costs you bear to be able to sell the part. There are holding costs to keep the part in good repair while in stock and ordering costs to replenish units you sell. Finally, sometimes you lose revenue from lost sales due to stockouts.  

These operating costs can be directly related to the way you manage the part in inventory. For our example, assume you use a (Q,R) inventory policy, where Q is the replenishment order quantity and R is the reorder point. Assume further that the reason you are not making $30 per unit is that you have competitors, and customers will get the part from them if they can’t get it from you.

Both your revenue and your costs depend in complex ways on your choices for Q and R. These will determine how much you order, when and therefore how often you order, how often you stock out and therefore how many sales you lose, and how much cash you tie up in inventory. It is impossible to cost out these relationships by guesswork, but modern software can make the relationships visible and calculate the dollar figures you need to guide your choice of values for Q and R. It does this by running detailed, fact-based, probabilistic simulations that predict costs and performance by averaging over a large number of realistic demand scenarios.  

With these results in hand, you can work out the margin associated with (Q,R) values using the simple formula

Margin = (Demand – Lost Sales) x Profit per unit sold – Ordering Costs – Holding Costs.

In this formula, Lost Sales, Ordering Costs and Holding Costs are dependent on reorder point R and order quantity Q.

Figure 1 shows the result of simulations that fixed Q at 25 units and varied R from 10 to 30 in steps of 5. While the curve is rather flat on top, you would make the most money by keeping on-hand inventory around 25 units (which corresponds to setting R = 20). More inventory, despite a higher service level and fewer lost sales, would make a little less money (and ties up a lot more cash), and less inventory would make a lot less.

Figure 1: Showing that there can be too little or too much inventory on hand

Without relying on the inventory simulation software, we would not be able to discover

• a) that it is possible to carry too little and too much inventory
• b) what the best level of inventory is
• c) how to get there by proper choices of reorder point R and order quantity Q.

Without an explicit understanding of the above, companies will make daily inventory decisions relying on gut feel and averaging based rule of thumb methods. The tradeoffs described here are not exposed and the resulting mix of inventory yields a far lower return forfeiting hundreds of thousands to millions per year in lost profits.  So be like Goldilocks.  With the right systems and software tools, you too can get it just right!    

Consider the problem of replenishing inventory. To be specific, suppose the inventory item in question is a spare part. Both you and your supplier will want some sense of how much you will be ordering and when. And your ERP system may be insisting that you let it in on the secret too.

Deterministic Model of Replenishment

The simplest way to get a decent answer to this question is to assume the world is, well, simple. In this case, simple means “not random” or, in geek speak, “deterministic.” In particular, you pretend that the random size and timing of demand is really a continuous drip-drip-drip of a fixed size coming at a fixed interval, e.g., 2, 2, 2, 2, 2, 2… If this seems unrealistic, it is. Real demand might look more like this: 0, 1, 10, 0, 1, 0, 0, 0 with lots of zeros, occasional but random spikes.

But simplicity has its virtues. If you pretend that the average demand occurs every day like clockwork, it is easy to work out when you will need to place your next order, and how many units you will need.  For instance, suppose your inventory policy is of the (Q,R) type, where Q is a fixed order quantity and R is a fixed reorder point. When stock drops to or below the reorder point R, you order Q units more. To round out the fantasy, assume that the replenishment lead time is also fixed: after L days, those Q new units will be on the shelf ready to satisfy demand.

All you need now to answer your questions is the average demand per day D for the item. The logic goes like this:

1. You start each replenishment cycle with Q units on hand.
2. You deplete that stock by D units per day.
3. So, you hit the reorder point R after (Q-R)/D days.
4. So, you order every (Q-R)/D days.
5. Each replenishment cycle lasts (Q-R)/D + L days, so you make a total of 365D/(Q-R+LD) orders per year.
6. As long as lead time L < R/D, you will never stock out and your inventory will be as small as possible.

Figure 1 shows the plot of on-hand inventory vs time for the deterministic model. Around Smart Software, we refer to this plot as the “Deterministic Sawtooth.” The stock starts at the level of the last order quantity Q. After steadily decreasing over the drop time (Q-R)/D, the level hits the reorder point R and triggers an order for another Q units. Over the lead time L, the stock drops to exactly zero, then the reorder magically arrives and the next cycle begins.

Figure 1: Deterministic model of on-hand inventory

This model has two things going for it. It requires no more than high school algebra, and it combines (almost) all the relevant factors to answer the two related questions: When will we have to place the next order? How many orders will we place in a year?

Probabilistic Model of Replenishment

Not surprisingly, if we strip away some of the fantasy from the deterministic model, we get more useful information. The probabilistic model incorporates all the messy randomness in the real-world problem: the uncertainty in both the timing and size of demand, the variation in replenishment lead time, and the consequences of those two factors: the chance of stock on hand undershooting the reorder point, the chance that there will be a stockout, the variability in the time until the next order, and the variable number of orders executed in a year.

The probabilistic model works by simulating the consequences of uncertain demand and variable lead time. By analyzing the item’s historical demand patterns (and excluding any observations that were recorded during a time when demand may have been fundamentally different), advanced statistical methods create an unlimited number of realistic demand scenarios. Similar analysis is applied to records of supplier lead times. Combining these supply and demand scenarios with the operational rules of any given inventory control policy produces scenarios of the number of parts on hand. From these scenarios, we can extract summaries of the varying intervals between orders.

Figure 2 shows an example of a probabilistic scenario; demand is random, and the item is managed using reorder point R = 10 and order quantity Q=20. Gone is the Deterministic Sawtooth; in its place is something more complex and realistic (the Probabilistic Staircase). During the 90 simulated days of operation, there were 9 orders placed, and the time between orders clearly varied.

Using the probabilistic model, the answers to the two questions (how long between orders and how many in a year) get expressed as probability distributions reflecting the relative likelihoods of various scenarios. Figure 3 shows the distribution of the number of days between orders after ten years of simulated operation. While the average is about 8 days, the actual number varies widely, from 2 to 17.

Instead of telling your supplier that you will place X orders next year, you can now project X ± Y orders, and your supplier knows better their upside and downside risks. Better yet, you could provide the entire distribution as the richest possible answer.

Figure 2 A probabilistic scenario of on-hand inventory

Figure 3: Distribution of days between orders

Climbing the Random Staircase to Greater Efficiency

Moving beyond the deterministic model of  inventory opens up new possibilities for optimizing operations. First, the probabilistic model allows realistic assessment of stockout risk. The simple model in Figure 1 implies there is never a stockout, whereas probabilistic scenarios allow for the possibility (though in Figure 2 there was only one close call around day 70). Once the risk is known, software can optimize by searching  the “design space” (i.e., all possible values of R and Q) to find a design that meets a target level of stockout risk at minimal cost. The value of the deterministic model in this more realistic analysis is that it provides a good starting point for the search through design space.

Summary

Modern software provides answers to operational questions with various degrees of detail. Using the example of the time between replenishment orders, we’ve shown that the answer can be calculated approximately but quickly by a simple deterministic model. But it can also be provided in much richer detail with all the variability exposed by a probabilistic model. We think of these alternatives as complementary. The deterministic model bundles all the key variables into an easy-to-understand form. The probabilistic model provides additional realism that professionals expect and supports effective search for optimal choices of reorder point and order quantity.