Should Cost vs Will Cost: What the Gap Between Them Tells You

What Should Cost Is

A should cost is the theoretical floor—what a supplier could profitably make a part for, given current market rates for materials, labor, energy, and equipment. It starts with the engineering specs, maps them to manufacturing processes, feeds in the prevailing market price for each input, and sums them up with a reasonable overhead and margin. It is a benchmark, an anchor point. It does not reflect what anyone is actually paying.

The calculation itself is defensible: materials databases, regional labor indices, equipment catalogs, and historical process yields are all public or purchasable. The rigor is in the comprehensiveness—did you price every material input at the right quality tier, account for scrap rates, recognize whether the process step is capital-intensive or labor-intensive, factor in tooling amortization? A weak should cost misses layers. A strong one maps the supplier's cost structure as accurately as public data allows.

What Will Cost Is

Will cost is what the supplier is actually quoting or charging. It is the real number. It reflects the should cost, yes, but also the supplier's margin strategy, its current capacity, its risk posture, and its assessment of your negotiating power. If a supplier sees you as a captive customer with no alternative, will cost climbs. If the supplier has excess capacity and needs your volume, will cost descends. Will cost is what you can actually buy for today.

Why the Two Numbers Differ

The gap between should cost and will cost exists because no supplier has optimized every element of its cost structure simultaneously. A few typical drivers:

Supplier efficiency. Your should cost assumes industry-average yields, labor rates, and material handling. A world-class supplier with proprietary process know-how, vertically integrated supply, or decades of volume runs the same part at lower actual cost than your model predicts. It quotes will cost closer to its true cost floor, not the industry average. That is earned margin, not gouging.

Volume leverage. The supplier you are quoting may already be running that part at high volume for someone else. Materials are bought in bulk, tooling is amortized across thousands of units, labor is trained and efficient. Your first-time order asks the supplier to step up the line and claim capacity. Will cost reflects that—higher, because you are not yet the incumbent. Over time, as your volume grows, the gap shrinks.

Market timing. Materials markets move. If your should cost assumes copper at $10,000/tonne but spot copper is at $14,000/tonne this month, the supplier's will cost has shifted. Your model lags. Similarly, if the supplier locked in material contracts three months ago at lower prices, its will cost reflects historical pricing, not current market. The gap widens or narrows with timing.

Negotiation leverage. This is the one most people fixate on. If you only have two qualified suppliers, both know their walk-away price is backed by your scarcity. Will cost rises. If you have ten suppliers and strong competitive pressure, will cost falls. Leverage is real, but it is not the whole story, and it does not make the gap a sign of unfair pricing—it is just the equilibrium between what the supplier can charge and what you can afford.

Should Cost vs Will Cost vs Landed Cost

A third term often conflates with both: landed cost. This is will cost plus all the costs to land the part in your facility—freight, duty, landed tariff, brokerage, insurance, logistics time. For imported goods, landed cost can be 15–30% higher than will cost. It is the true all-in number for decision-making, but it is not a manufacturing cost; it is a procurement cost. When comparing should cost, will cost, and landed cost, all three are real but answer different questions: should cost answers what is this part worth, will cost answers what are we paying today, and landed cost answers what is our true cost to inventory this part in our warehouse.

What the Gap Tells You

A gap between should cost and will cost is not evidence of overcharging. It is a signal.

A small gap (0–10%) suggests the supplier is competitive, its cost structure is transparent, and margin is tight. This is either a commodified part with many bidders or a mature supplier relationship. Negotiation headroom is limited. Your energy is better spent on volume commitments or design changes that reduce the part cost itself.

A moderate gap (10–30%) suggests the supplier has earned margin through efficiency, volume position, or risk management. This is healthy and normal. The supplier is neither desperate nor unchallenged. Negotiation can move the needle, but you are negotiating with a solvent partner who has less incentive to cut corners. For cost engineering teams, this is the band where conversations shift from "lower your price" to "let's engineer the part cost down together."

A large gap (30%+) signals that either your should cost model is incomplete (you are missing a process step, material variant, or market dynamic the supplier sees) or the supplier has unusual market power or efficiency. Before accusing the supplier of margin gouging, audit your should cost. Run a cost driver analysis. Is there a supplier-side exclusive process? A material you did not account for? A regional labor cost you got wrong? Often the gap reveals a modeling gap, not a pricing one.

The key: a gap is information. Act on it by understanding its source, not by assuming malice.

Why the Gap Goes Stale

A should cost is valid for as long as its input assumptions hold. Material prices shift monthly. Labor markets tighten or loosen. Currency exchange rates move. A supplier's capacity posture changes. If you ran your should cost three months ago and the market has moved—input costs up 8%, exchange rates shifted 5%, competitor entry reshaped the supply landscape—your model is stale. Will cost has already moved. The gap has widened or narrowed. You think you have negotiation headroom; you are out of date.

This is why cost modeling teams need continuous modeling, not spreadsheets built once and read quarterly. The should-cost baseline should update whenever material indices move or market conditions shift. Then the gap stays fresh. Then negotiation targets stay realistic. Then you are not walking into a supplier meeting with a three-month-old should cost and no idea that the market has already repriced your leverage away.

Muir's BoM comprehension capability handles this automation. When you load a Bill of Material (BoM) into the system, it maps each line item to current material indices, supplier cost data, and process-capability libraries. The should-cost model updates the same day material markets move. The gap stays current, and your cost engineering team spends its time on value-add decisions—design tradeoffs, supplier strategies, scenarios—not rebuilding models by hand every time aluminum moves $50/tonne.

Closing

The gap between should cost and will cost is not the enemy. It is the question. Ask what it means. Is your supplier's margin fair given its efficiency or risk? Is your should cost missing something the supplier sees? Are you reading the market correctly, or is your model three months stale? A cost engineering leader who understands the gap owns the negotiation, not just the spreadsheet.