Learning Outcomes

After completing this lesson, learners will be able to:

• Explain inventory optimisation.
• Assess inventory performance using standard measures.
• Explain postponement, Vendor-Managed Inventory, cross-docking and quick-response systems.
• Describe how the number of inventory locations affects total inventory.
• Explain the financial impact of inventory.
• Evaluate the trade-off between inventory-carrying cost and customer service.
• Distinguish between the direct and indirect costs of poor inventory management.
• Identify suitable inventory-improvement actions.

1. Inventory Optimisation

Inventory optimisation determines the appropriate quantity and location of inventory needed to achieve customer-service requirements at an acceptable cost and level of risk.

It considers:

• Customer demand
• Service-level targets
• Lead times
• Forecast accuracy
• Supply reliability
• Order quantities
• Safety stock
• Inventory locations
• Product characteristics
• Inventory costs
• Operational risks

The objective is not simply to minimise stock. It is to maintain the inventory required to support operations and customers without holding unnecessary quantities.

2. Inventory Optimisation Balance

Inventory decisions affect both customer service and financial performance.

Too little inventory
        ↓
Stockouts, delays and lost sales

Appropriate inventory
        ↓
Demand is met at a controlled cost

Too much inventory
        ↓
Higher costs, tied-up cash and obsolescence

Optimisation seeks the middle position appropriate to the organisation’s demand, risk and service requirements.

3. Inventory-Performance Measures

Inventory Turnover

Inventory turnover measures how frequently average inventory is sold or used during a period.

Inventory turnover = Cost of goods sold ÷ Average inventory value

A higher turnover may indicate efficient inventory use. However, turnover that is too high may be associated with shortages.

Days of Inventory

Days of inventory estimates how long the organisation’s average inventory will last.

Days of inventory = 365 ÷ Inventory turnover

Fewer days may reduce holding costs, but insufficient stock can threaten service continuity.

Inventory Accuracy

Inventory accuracy compares recorded inventory with physical inventory.

Inventory accuracy = Correct inventory records ÷ Total records checked × 100

Low accuracy can cause incorrect purchasing and order promises.

Fill Rate

Fill rate measures the proportion of customer demand supplied from available inventory.

Fill rate = Demand fulfilled immediately ÷ Total demand × 100

Stockout Rate

Stockout rate measures how often required products are unavailable.

Carrying-Cost Percentage

This measures the annual cost of holding inventory relative to its value.

Obsolescence Rate

This measures inventory that has become outdated or unsuitable.

Shrinkage

Shrinkage is inventory lost through:

• Theft
• Damage
• Unrecorded use
• Administrative errors
• Supplier discrepancies
• Handling losses

Forecast Accuracy

Forecast accuracy assesses how closely expected demand matches actual demand.

4. Balanced Inventory Measurement

No single measure provides a complete picture.

Inventory performance should therefore be evaluated across:

• Cost
• Availability
• Accuracy
• Speed
• Quality
• Risk

5. Inventory-Optimisation Process

1. Establish customer-service requirements.
2. Classify inventory.
3. Analyse historical and forecast demand.
4. Assess lead times and supply risk.
5. Calculate suitable replenishment parameters.
6. Review inventory locations.
7. Identify excess, obsolete and slow-moving stock.
8. Select appropriate replenishment strategies.
9. Monitor performance measures.
10. Correct deviations.
11. Review the results continuously.

6. Postponement

Postponement delays the final production, assembly, packaging or allocation of a product until more accurate demand information is available.

Example

A manufacturer produces a standard product but delays applying language-specific labels and regional packaging until confirmed customer orders are received.

Benefits

• Lower finished-goods inventory
• Reduced forecast risk
• Greater flexibility
• Lower obsolescence
• Improved product customisation

Challenges

• Requires flexible processes
• May increase final processing time
• Requires suitable product design
• Depends on reliable information
• May require specialised facilities

7. Vendor-Managed Inventory

Vendor-Managed Inventory, or VMI, allows a supplier to monitor and replenish inventory for a customer.

The customer shares inventory, sales or consumption information with the supplier.

Benefits

• Reduced ordering administration
• Improved replenishment
• Better product availability
• Greater supplier visibility
• Reduced stockouts
• Improved coordination

Risks

• Dependence on the supplier
• Inaccurate or delayed information
• Unclear inventory ownership
• Excessive replenishment
• Data-security concerns
• Weak accountability

A VMI agreement should define:

• Minimum and maximum levels
• Ownership
• Replenishment authority
• Performance measures
• Information-sharing arrangements
• Responsibilities for excess or obsolete stock

8. Cross-Docking

Cross-docking moves goods from receiving directly to dispatch with little or no storage.

Inbound vehicle
      ↓
Receiving and sorting
      ↓
Outbound staging
      ↓
Outbound vehicle

Benefits

• Reduced storage
• Shorter handling time
• Faster product flow
• Lower inventory levels
• Reduced warehouse-space requirements

Requirements

• Accurate schedules
• Reliable suppliers
• Correct product information
• Coordinated inbound and outbound transport
• Suitable facility layout
• Rapid identification and sorting

Risks

A delay in an inbound shipment may affect several outbound deliveries because little buffer inventory is available.

9. Quick-Response Systems

Quick-response systems use current demand information to replenish inventory rapidly.

They may combine:

• Point-of-sale data
• Electronic ordering
• Automated replenishment
• Short production cycles
• Frequent deliveries
• Shared supplier information

Benefits

• Lower inventory
• Faster reaction to demand
• Reduced stockouts
• Less obsolete stock
• Improved forecast updates

Requirements

• Accurate information
• Integrated systems
• Reliable suppliers
• Short lead times
• Flexible transport
• Frequent performance monitoring

10. Comparing Inventory-Reduction Approaches

These approaches reduce inventory in different ways and should be selected according to operational conditions.

11. Inventory Locations

Inventory may be held in:

• A central warehouse
• Regional distribution centres
• Local depots
• Retail stores
• Supplier facilities
• Customer sites
• Goods-in-transit locations

The number and position of locations affect inventory, transport cost and customer service.

12. Centralised Inventory

Centralisation holds inventory at fewer locations.

Potential Advantages

• Lower total safety stock
• Easier control
• Reduced facility costs
• Better inventory visibility
• Lower duplication
• Easier specialised handling

Potential Disadvantages

• Longer customer delivery distances
• Higher outbound transport cost
• Greater dependence on one facility
• Slower response to remote markets
• Increased disruption impact

13. Decentralised Inventory

Decentralisation holds inventory at several regional or local locations.

Potential Advantages

• Faster delivery
• Greater proximity to customers
• Improved regional responsiveness
• Reduced last-mile distance
• Some protection against a single-location failure

Potential Disadvantages

• Higher total safety stock
• Duplicate inventory
• Additional facilities
• Increased operating costs
• Greater coordination complexity
• Higher risk of stock imbalances

14. Number of Locations and Inventory Level

As the number of inventory locations increases, total safety stock generally increases because each location must protect itself against uncertainty.

For example, separate depots in Gauteng, KwaZulu-Natal and the Western Cape may each hold safety stock for the same product.

This can improve regional service but increase:

• Total inventory
• Facility cost
• Obsolescence risk
• Inventory imbalance
• Administrative complexity

The network decision must balance customer response time with total supply chain cost.

15. Financial Impact of Inventory

Inventory is an asset, but it requires cash and creates ongoing costs.

Working Capital

Money invested in inventory is unavailable for other business requirements.

Excess stock can weaken cash flow even when the organisation appears profitable.

Storage and Handling

Inventory requires:

• Warehouse space
• Employees
• Equipment
• Utilities
• Security
• Insurance
• Information systems

Damage and Deterioration

Products may lose value through:

• Physical damage
• Expiry
• Contamination
• Rust
• Moisture
• Incorrect handling

Obsolescence

Inventory may become obsolete because of:

• Technology changes
• Product redesign
• Regulation changes
• Customer preferences
• Packaging changes
• Project cancellation

Financing Cost

If borrowed funds are used to purchase inventory, the organisation may incur interest and other financing costs.

16. Inventory-Carrying Cost

Inventory-carrying cost is the total cost of holding inventory over a period.

It may include:

• Cost of capital
• Storage
• Insurance
• Handling
• Security
• Damage
• Shrinkage
• Expiry
• Obsolescence

A simplified estimate is:

Annual carrying cost = Average inventory value × Carrying-cost percentage

Example

Average inventory value is R2,000,000 and the annual carrying-cost percentage is 20%.

Annual carrying cost = R2,000,000 × 20%
Annual carrying cost = R400,000

17. Inventory and Customer-Service Trade-Off

Higher inventory may provide:

• Greater product availability
• Faster fulfilment
• Fewer stockouts
• Improved customer confidence

However, it may also create:

• Higher holding costs
• More capital tied up
• Greater obsolescence
• Increased storage requirements

Lower inventory may reduce costs but increase:

• Stockout risk
• Back orders
• Emergency purchasing
• Expedited transportation
• Lost sales
• Customer dissatisfaction

The appropriate balance depends on:

• Customer-service targets
• Product importance
• Lead-time reliability
• Demand variability
• Stockout consequences
• Inventory cost

18. Direct Costs of Poor Inventory Management

Direct costs can be measured and linked clearly to inventory activities.

Examples include:

• Excess storage
• Emergency transport
• Expedited purchasing
• Product write-offs
• Damage
• Shrinkage
• Obsolescence
• Stock-counting corrections
• Production downtime
• Contractual penalties

19. Indirect Costs of Poor Inventory Management

Indirect costs may be less visible but can have a serious long-term effect.

Examples include:

• Lost customer trust
• Reputational damage
• Lost future sales
• Reduced employee productivity
• Poor supplier relationships
• Management time spent resolving problems
• Delayed projects
• Reduced competitiveness
• Inaccurate planning decisions

20. South African Inventory Considerations

Inventory decisions in South Africa may need to consider:

• Long distances between major centres
• Dependence on road freight
• Port and border delays
• Imported-product lead times
• Currency fluctuations
• Infrastructure disruptions
• Security risks
• Rural distribution requirements
• Supplier concentration

An organisation may hold additional inventory to protect against these risks, but the financial cost must be measured.

21. Improving Inventory Performance

Possible improvement actions include:

• Correcting inaccurate inventory records
• Reviewing reorder points
• Adjusting safety stock
• Improving forecasts
• Reducing supplier lead times
• Applying ABC controls
• Removing obsolete stock
• Consolidating locations
• Using postponement
• Implementing VMI
• Introducing cross-docking
• Improving system integration
• Monitoring performance regularly

Improvements should address verified causes rather than simply reducing inventory across all products.

22. Lesson Summary

• Inventory optimisation balances availability, cost and risk.
• Performance must be assessed using several measures rather than one measure alone.
• Postponement delays final product configuration until demand is clearer.
• VMI gives the supplier responsibility for agreed replenishment decisions.
• Cross-docking reduces storage by moving products rapidly from receiving to dispatch.
• Quick-response systems use current demand information for rapid replenishment.
• Increasing inventory locations generally increases total safety stock.
• Inventory affects working capital, cash flow, storage costs and profitability.
• Higher inventory may improve service but increases carrying cost and financial exposure.
• Poor inventory management creates both direct and indirect costs.