Total Cost of Ownership (TCO) in Purchasing: Supplier Selection and Green Procurement

In brief: A situation frequently seen in practice is that, after a tender is awarded to the lowest bid, freight, rejection, and excess stock costs emerge within a few months. The main reason is that the offer with the lowest unit price often does not correspond to the lowest-cost supplier. Total cost of ownership (TCO) adds transportation and customs, quality, inventory carrying, administration, and risk costs to the unit price and makes suppliers comparable. This article covers the components of TCO, a numerical example with two suppliers, and how green procurement criteria can be included in supplier selection.

Why Is Unit Price Misleading?

The low unit price of a distant supplier can rarely be evaluated on its own. It is accompanied by higher freight and customs, extra safety stock caused by the long lead time, a larger minimum order quantity, and currency and delay risk. A significant part of these costs does not appear in the purchasing budget; they are spread across the logistics, quality, warehouse, and finance budgets. The function of TCO is to collect these scattered costs in a single comparison table.

What Are the Components of TCO?

Example: TCO Comparison of Two Suppliers

Assume there are two offers for a component used at 10,000 units per year. A is a distant supplier and B is a nearby one. The inventory carrying cost rate is assumed to be 25% per year (figures are for illustration purposes; CU: currency unit).

The line in the table that requires the most explanation is inventory carrying cost. A's minimum order quantity is 5,000 units; because of the long lead time, safety stock is also 1,500 units. Average stock is 5,000 / 2 + 1,500 = 4,000 units, and the delivered unit cost is 8.70 CU. The annual carrying cost is 4,000 × 8.70 × 25% = 8,700 CU, which corresponds to 0.87 CU per unit. For B, the order quantity is 1,000 and safety stock is 300 units; the calculation (500 + 300) × 9.15 × 25% = 1,830 CU gives about 0.18 CU per unit.

With this calculation the ranking is reversed. A's unit price is 11% lower; nevertheless, B's total cost of ownership is 0.54 CU lower per unit, and about 5,400 CU lower per year. In case the carrying rate may have been overestimated, when the rate is reduced to 15%, A is 9.62 and B is 9.36, and the ranking does not change. It is recommended to add such a sensitivity check to every TCO report; management, seeing to what extent the result depends on which assumption, trusts the analysis more easily.

How Are Green Procurement Criteria Added?

The basic reference on this subject is the ISO 20400 sustainable procurement guidance. The guidance recommends embedding environmental and social criteria in every stage of procurement rather than adding them at the end of the process. Criteria frequently used in supplier selection are listed below:

• Product carbon footprint or environmental product declaration (EPD)
• The supplier's scope 1 and 2 emissions data and reduction targets
• Share of recycled or renewable content
• Packaging reduction and use of returnable packaging
• Transport distance and mode
• Environmental management system (e.g., ISO 14001) and social compliance audits

There are two ways of reflecting these criteria in the decision: (1) monetizing emissions with an internal carbon price and adding them directly to TCO; (2) evaluating them as a separate dimension alongside TCO with weighted scoring. The table below shows the second approach (1-5 points):

Weights must be determined according to the organization's priorities and before offers are received. Weights determined afterwards often serve to justify a decision made in advance.

How Is TCO Linked to Planning?

The moment purchasing selects a supplier, the planning parameters are also largely determined. Lead time and its variability affect safety stock (see 5 Common Mistakes in Safety Stock Calculation), minimum order quantity affects average stock, and supplier capacity affects the options in the S&OP supply review. In practice, the planning team is often seen to learn of this decision only when the order is opened. For strategic items, it is recommended that the decision be made together with the planning team's parameter calculations.

The criterion on which supplier selection is based should not be unit price;
what is decisive is the total cost of the material to the organization.

Technology and Digitalization: Digital Decision Support in Purchasing

TCO calculation and the supplier scorecard become reliable only when costs other than price (delay, quality, inventory, transportation) are measured regularly. A manually maintained scorecard is updated in most companies once a year, during the supplier evaluation period. When order and delivery records are kept digitally, the same data accumulates automatically with each order.

Enterprise Resource Planning (ERP) is the enterprise transaction system that records orders, inventory, purchasing, production, and finance transactions in a common database; it is the master data and transaction source for planning. It is the source of price, delivery date, quality rejection, and invoice data, and allows the calculation of TCO components and the supplier scorecard.

E-Procurement is a purchasing structure in which the request, quotation, approval, and order steps are carried out in a traceable way through digital workflow. It makes all steps from request to order traceable and standardizes the comparison of quotations with TCO criteria.

Electronic Data Interchange (EDI) is the transfer of documents such as orders, call-offs, shipping notices, and invoices between companies in a standard format without human intervention. It transfers order, confirmation, and shipment documents automatically and makes it easier to compare committed and actual delivery dates.

Internet of Things (IoT) is the infrastructure in which sensors on machines, vehicles, warehouses, and products transmit data automatically over a network; location, temperature, status, and consumption data are collected without human input. Through container and vehicle tracking, it makes lead time variability measurable; this data is directly reflected in the inventory and delay costs in TCO.

Artificial Intelligence (AI) and Machine Learning (ML) are methods that learn patterns from data to produce forecasts, classifications, and recommendations; machine learning is the sub-field of artificial intelligence that learns from data. They categorize spend, detect supplier risk signals (delay trend, quality deviation) at an early stage, and help extract important clauses from contracts.

Business Intelligence (BI) is the analytics layer that combines data from different sources and presents it to decision makers through dashboards and reports. It presents the supplier scorecard and category-level TCO analysis through dashboards.

Division of tasks between artificial intelligence and the purchasing team. Artificial intelligence contributes most to preparation and monitoring work in purchasing. Classifying scattered spend items, comparing offers in different formats on the same basis, and early detection of deviations in a supplier's delivery performance are among these tasks. Criterion weights, strategic supplier relationships, and the final selection remain the responsibility of the purchasing team.

The invoice shows the unit price, while the scorecard shows the total cost;
the right decision can be made by evaluating the two pieces of information together.

Implementation: Checklist

1. Identify strategic and high-spend items; start the TCO analysis with them.
2. Fix the inventory carrying cost rate as a single value together with finance.
3. Define the data sources (logistics, quality, warehouse) for the TCO components.
4. Approve the evaluation criteria and their weights before offers arrive.
5. Add sustainability criteria to the decision by monetizing them or through weighted scoring.
6. Show the sensitivity of the result to the main assumptions in the report.
7. Generate the supplier scorecard automatically from ERP data (on-time delivery, quality, price); move TCO items from scattered spreadsheets to a common data source.

Related Articles

• 5 Common Mistakes in Safety Stock Calculation and the Correct Approach
• Sustainability in the Supply Chain: Scope 3 Emissions, CBAM, and Their Effects on Planning
• Spare Parts Planning in Defense and Aerospace: Repair Cycle, Criticality, and Obsolescence

Frequently Asked Questions

For which items should TCO analysis be performed?

It is recommended to start the analysis with high-spend and strategic items, that is, materials that are single-sourced, have long lead times, or carry high quality risk. A simplified calculation is sufficient for low-value routine items.

Does green procurement increase cost?

It may increase the unit price. However, evaluated in terms of TCO, less packaging, shorter transport distances, and less scrap can reduce total cost. In addition, carbon costs such as CBAM directly make high-emission materials more expensive.

Can an ISO 20400 certificate be obtained?

No. ISO 20400 is a guidance standard and is not used for certification. It explains how to embed sustainability criteria into procurement policy and processes.

How is the inventory carrying cost rate determined?

The cost of capital, storage, insurance, obsolescence, and scrap costs are added up and divided by average inventory value. It is recommended that this rate be determined once together with the finance unit and that the same value be used in all TCO and inventory calculations; otherwise, each analysis will give a different result.

Can artificial intelligence make supplier selection?

It cannot do so on its own. It makes an important contribution in classifying data, detecting risk signals, and comparing offers. Criterion weights, assessment of strategic relationships, and the final decision should remain the responsibility of the purchasing team.

References

• Ellram, L. M. (1995). Total cost of ownership: an analysis approach for purchasing. International Journal of Physical Distribution & Logistics Management, 25(8), 4-23.
• ISO 20400:2017. Sustainable procurement, Guidance.
• Kraljic, P. (1983). Purchasing must become supply management. Harvard Business Review, 61(5), 109-117.

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