What is Sunk Costs (Economics)?

Sunk Costs (Economics) is a mental model used for better thinking and decision-making.

How do you apply Sunk Costs (Economics)?

To apply Sunk Costs (Economics), identify situations where this framework is relevant, then use it as a lens to evaluate your options and decisions. The model is most useful when combined with other complementary mental models.

What category does Sunk Costs (Economics) fall under?

Sunk Costs (Economics) falls under the Economics & Markets category of mental models. Other models in this category can be found on the Economics & Markets hub page.

Why is Sunk Costs (Economics) important?

Sunk Costs (Economics) is important because it provides a structured way to think about problems that would otherwise be approached with intuition alone. Understanding this model helps you avoid common reasoning errors and make better decisions.

Sunk Costs (Economics) Mental Model…

Sunk Costs (Economics) Mental Model… | Faster Than Normal

Economics & Markets

Section 1

The Core Idea

Sunk costs are past expenditures of time, money, or effort that cannot be recovered. In economic logic, they are irrelevant to the current decision. What matters is the marginal path forward: the future costs and benefits of each option. The $10m already spent on a failing project doesn't disappear if you shut the project down — but it doesn't increase if you keep going. The only question is whether the next dollar and the next hour produce more value in this project or somewhere else.

The principle is simple. Rational choice depends on comparing the expected outcomes of available actions from this moment on. Sunk costs are the same regardless of which action you take; they cancel out of the comparison. So they should not tilt the decision. In practice, people and organisations routinely let sunk costs dictate continuation. "We've come this far." "We can't waste what we've invested." The emotional and political weight of the past distorts the marginal calculus. The discipline is to separate "what we've spent" from "what we'll get if we continue" and to decide only on the latter.

The strategic use: before committing more resource to any project, product, or strategy, ask what the incremental return is. If the next unit of investment has a higher return elsewhere, reallocate. The sunk cost is not a reason to continue; it is a reason to be clear-eyed about the marginal decision so you don't compound the error.

Salvage value is the exception. If stopping or switching frees resources that can be used elsewhere — selling equipment, reassigning people, repurposing code — that recovery is a future benefit of the exit option. It belongs in the marginal comparison. Only the part that cannot be recovered under any choice is truly sunk. In practice, people overstate how much is sunk (they forget salvage) and understate how much is salvageable (they don't look for it). Both errors bias toward continuing.

Example in practice. A company had spent three years and $15m building an internal ERP. The system worked but was costly to maintain and limited flexibility. The CFO argued for one more year to "get value from what we've built." The right question: from today, is the expected return from the next dollar and the next engineer-year higher in fixing the ERP or in migrating to a best-in-class SaaS product? The $15m is sunk. The migration cost is a future cost of the "quit" option; the benefit is future flexibility and lower TCO. The marginal comparison favoured migration. They migrated; the sunk cost was written off; the business improved.

Sunk Costs (Economics)

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