# Opportunity Cost: The Price of What You Didn't Choose

> Opportunity cost is the value of the best option you give up when you choose. See the definition, how to calculate it, examples and the common mistakes.

Canonical: https://mentarium.io/mental-models/opportunity-cost.md

Mental model

6 min read By [Nemo](https://mentarium.io/about) Updated October 30, 2026

> **Opportunity cost** is the value of the best alternative you give up when you make a choice. Every use of money, time or attention rules out other uses, so the real cost of anything is not just what you pay, but what that money, time or attention could have done in its next-best use.

- **Category**: Mental model (economics and trade-offs)
- **Origin**: Friedrich von Wieser, late 19th century; Frédéric Bastiat, 1850
- **Best used for**: Spending, career moves and how you use your time
- **Related**: Sunk cost, regret minimization, expected value

## Ask yourself

- What is the best thing I could do with this money, time or attention instead?
- If I weren't already doing this, would I start it today?
- What am I saying no to by saying yes here?
- Is the option I'm comparing against real, or one I'd never actually do?
- What does this choice cost me in a year, not just today?

## What is opportunity cost?

Opportunity cost is the value of the best option you give up when you choose something. The real price of anything is not only what you pay, but what that same money, time or attention could have done instead.

Every choice is a trade. A $40,000 car costs $40,000, but it also costs whatever that money would have become if you had invested it, paid down debt or used it to start a business. A year spent on a master’s degree costs tuition, plus the salary and experience you would have earned in that year.

The model’s power is that it makes the invisible visible. Prices are printed. Alternatives are not. Most people compare an option with doing nothing, when the honest comparison is with the next-best thing they could do.

## Where does opportunity cost come from?

The term comes from economics. The Austrian economist Friedrich von Wieser is usually credited with naming and developing the concept in the late 19th century, as part of the Austrian school’s view that value comes from what people give up to get something.

The idea is older. In 1850, the French economist Frédéric Bastiat published “That Which Is Seen, and That Which Is Not Seen.” His famous example: a broken shop window gives the glazier work, so some people call it good for the economy. Bastiat pointed out the unseen cost: the shopkeeper would have spent that money on something else, like shoes or books, and now can’t. The repair is seen; the lost alternative is not.

Psychologists later studied why we miss these costs. Research on “opportunity cost neglect,” including work by Shane Frederick and colleagues published in 2009, found that people deciding whether to buy something often fail to think about what else the money could buy, and that simply reminding them of the alternative made them more likely to keep the money. The cost was there all along. It just wasn’t on their mind.

## How to use opportunity cost

You use opportunity cost by naming the specific best alternative for each choice and comparing against it, not against nothing. The steps:

1. **Name the resource.** Money, time, attention, energy or reputation. Many big decisions spend more than one.
2. **List the realistic alternatives.** What would you actually do with this resource otherwise? Not fantasy options, real ones.
3. **Pick the best alternative.** That one, and only that one, is the opportunity cost.
4. **Estimate both values.** In money where you can, in rough terms where you can’t. [Expected value](https://mentarium.io/mental-models/expected-value) helps when outcomes are uncertain.
5. **Ask the fresh-start question.** “If I weren’t already doing this, would I start it today?” It strips out the past and leaves only the forward trade.
6. **Ignore what’s already spent.** Money and time you can’t recover are [sunk costs](https://mentarium.io/mental-models/sunk-cost). They don’t belong in the comparison.
7. **Decide, and note what you gave up.** Writing “I chose X over Y” makes the trade explicit and gives you something to review later.

A useful shortcut for small purchases: translate the price into a concrete alternative. “This gadget is two weekends away” or “this subscription is a week of groceries a year.”

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## 3 real-world examples

### Business

Say a small agency is offered a large, low-margin client. On its own, the client looks like pure gain: more revenue. The opportunity cost question is: what would the team do with those hours otherwise? If the honest answer is “pitch two higher-margin clients we’ve been too busy to chase,” the big client may cost more than it pays. If the answer is “sit idle,” taking it is easy.

### Personal life

Say you’re offered a promotion that adds 15 hours a week. The visible gain is salary and title. The opportunity cost is what those 15 hours currently do: time with young kids, a side project, sleep, health. None of these come with a price tag, which is why they get underweighted. Naming them doesn’t decide the question, but it makes it a real comparison instead of “more money vs nothing.” The [regret minimization framework](https://mentarium.io/mental-models/regret-minimization-framework) is a good partner here.

### Investing

Say you’ve held a stock for years and it’s flat. Many investors keep it because selling would “lock in” a loss compared with what they paid. Opportunity cost says the purchase price is irrelevant. The question is whether this money is likely to do better here or in your best alternative, whether that’s an index fund or paying off a loan. Every day you hold, you’re implicitly choosing it over everything else.

## Common mistakes

The most common mistake is comparing an option with doing nothing instead of with your best real alternative. Others:

- **Counting every alternative.** The opportunity cost is the single best option you gave up, not the sum of all of them.
- **Using fantasy alternatives.** “That money could have been in a stock that went up tenfold” isn’t a real alternative unless you would have picked it.
- **Letting sunk costs in.** What you already spent is gone either way. It changes how a choice feels, not what it costs from here on.
- **Ignoring non-money costs.** Time, health and attention are the scarcest resources most people have, and they rarely show up in a spreadsheet.
- **Paralysis.** Everything has an opportunity cost. For small, [reversible decisions](https://mentarium.io/mental-models/reversible-decisions), a rough guess is enough.

## Opportunity cost vs sunk cost

Opportunity cost looks forward at what you’ll give up; sunk cost looks backward at what you’ve already spent. Good decisions count the first and ignore the second.

|  | Opportunity cost | Sunk cost |
|---|---|---|
| Time direction | Future | Past |
| Question | What else could this do from now on? | What have I already put in? |
| Should it affect the decision? | Yes, always | No (only as information, not as a reason) |
| Typical error | Ignoring it because it’s invisible | Counting it because it’s painful |
| Related bias | Opportunity cost neglect | [Sunk cost fallacy](https://mentarium.io/biases/sunk-cost-fallacy) |
| Example | A job offer costs the career you’d build elsewhere | Three years in a degree you no longer want |

## The Mentarium take

Opportunity cost is the most important idea in economics that almost nobody uses in daily life. People don’t fail to understand it; they fail to remember it at the moment of choice. The alternative is silent, and silence loses to a price tag every time.

The fix is mechanical, and that’s the point. In the Map step of the Mentarium Decision Loop (Frame → Map → Stress-test → Decide → Review), every option gets a line that says “instead, I could…” with the best real alternative. If you can’t fill that line, you haven’t mapped the decision yet.

It anchors two of our standard Model Stacks. Quitting a job = Opportunity Cost + Regret Minimization + Reversible vs irreversible decisions. Big purchase = Opportunity cost + Margin of safety + Ten-ten-ten rule. In both, opportunity cost does the same job: it turns “should I?” into “is this better than my next-best option?”, which is the only question that ever mattered.

One habit we recommend: in your decision journal, write down the option you gave up next to every big choice. When you review it later, you won’t only learn whether your choice worked. You’ll learn whether your alternative would have been better, which is how you get better at choosing between them.

**Counters** [Sunk Cost Fallacy](https://mentarium.io/biases/sunk-cost-fallacy)

## FAQ

### What is opportunity cost in simple terms?

It is what you give up when you choose one thing over another. If you spend Saturday painting the fence, the opportunity cost is the best other thing you could have done with that Saturday, whether that's earning money, resting or seeing friends.

### How do you calculate opportunity cost?

In its simplest form: the return of the best option you didn't choose minus the return of the option you did choose. For money, compare expected returns. For time or wellbeing, the numbers are rough, but naming the alternative still makes the cost visible.

### What is the difference between opportunity cost and sunk cost?

Opportunity cost looks forward: what you give up from now on. Sunk cost looks backward: money or time already spent that you can't recover. Good decisions count opportunity costs and ignore sunk costs.

### Who came up with opportunity cost?

Austrian economist Friedrich von Wieser is usually credited with naming and developing the concept in the late 19th century. Earlier, Frédéric Bastiat's 1850 essay on "what is seen and what is not seen" made the same point about hidden alternatives.

### Why do people ignore opportunity cost?

Because the alternative is invisible. The price of a purchase is printed on the tag, but the thing you would have done with that money isn't. Research on opportunity cost neglect suggests people weigh it more when they are simply reminded of it.

## Related models & biases

[Mental model Sunk Cost A sunk cost is any money, time or effort already spent that cannot be recovered whatever you decide next. As a mental model, it means pricing the past out of the decision: you compare only the future costs and benefits of each option, starting from where you stand today.](https://mentarium.io/mental-models/sunk-cost) [Mental model Regret Minimization Framework The regret minimization framework is a decision method in which you imagine yourself near the end of your life, around age 80, and ask which option you would be least likely to regret. Associated with Jeff Bezos, it helps with big, personal choices where short-term fear hides long-term priorities.](https://mentarium.io/mental-models/regret-minimization-framework) [Mental model Expected Value Expected value is the average result you would get from a choice if you could make it many times: each possible outcome multiplied by its probability, then added up. It lets you compare risky options on one number, as long as you also check the worst case, since a good average can hide a ruinous outcome.](https://mentarium.io/mental-models/expected-value) [Mental model One-Way vs Two-Way Door Decisions Reversible vs irreversible decisions is the idea that how carefully you decide should depend on how easily you can undo the choice. Jeff Bezos called them two-way doors (reversible, decide fast) and one-way doors (irreversible, decide slowly) in his 2015 shareholder letter. Most decisions are two-way doors treated like one-way doors.](https://mentarium.io/mental-models/reversible-decisions) [Cognitive bias Sunk Cost Fallacy The sunk cost fallacy is the tendency to keep investing in a project, plan or relationship because of the time, money or effort already spent, even when the future costs outweigh the future benefits. Past costs cannot be recovered, so a rational choice ignores them and compares only what lies ahead.](https://mentarium.io/biases/sunk-cost-fallacy)

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