- The hidden cost most owners miss: their own unpaid time
- The catch: a profit on paper, a loss in economic terms
- CFI's oil field: the same idea at a much bigger scale
- How finance teams build it into a decision
- Why sunk costs stay out of the sum
- How to work out opportunity cost in six steps
- Where I come in
- My verdict
- Frequently asked questions
Opportunity cost is the value of the next best option you give up when you make a choice. Corporate Finance Institute (CFI) puts it in one line: it's the cost of what else you could have chosen to do.
CFI points out that opportunity cost only exists when there's a choice. If you've got one option, the alternative is doing nothing, and that costs nothing. If you're choosing between A and B, the opportunity cost of A is the net benefit you'd have had from B, and the other way round.
OpenStax, the free economics textbook, adds the part that matters most for a small business. Opportunity cost is measured by what you give up, and while you can sometimes put a cash figure on it, it's often more useful to think in time or in the resources you hand over.
The hidden cost most owners miss: their own unpaid time
OpenStax splits costs into two kinds. Explicit costs are out-of-pocket payments such as wages and office rent. Implicit costs are the opportunity cost of using resources the business already owns. For small businesses, OpenStax says these are often things the owner contributes: working in the business without a formal salary, or using the ground floor of a home as a shop.
| Cost type | What it means (OpenStax) | Small business example |
|---|---|---|
| Explicit | An out-of-pocket payment | Wages, office rent |
| Implicit | The opportunity cost of resources you already own | Working without a salary, running a shop from your own ground floor |
Wikipedia gives a small everyday version. If you spend an hour and $200 buying office supplies, and your time is worth $25 an hour, the explicit cost is $200 and the implicit cost is the $25 of your hour (Wikipedia's figures, as of October 2026).
The catch: a profit on paper, a loss in economic terms
OpenStax's Eryn example is the clearest illustration I've seen. Eryn earns $125,000 a year at a law firm. She's thinking about opening her own practice, which she expects to bring in $200,000 a year. Office rent would be $50,000 and a law clerk $35,000. These are OpenStax's US dollar figures, as of October 2026.
| Item | Eryn's own practice (OpenStax example) |
|---|---|
| Expected revenue | $200,000 |
| Explicit costs (rent $50,000 + clerk $35,000) | $85,000 |
| Accounting profit | $115,000 |
| Implicit cost (the salary she gives up) | $125,000 |
| Economic profit | -$10,000 |
On paper, her practice makes $115,000. But once you count the salary she'd walk away from, her economic profit is minus $10,000 a year. OpenStax is careful here: that doesn't mean she shouldn't open the firm. It means she'd earn $10,000 less than she does now, and she might decide independence is worth that. It also notes that lost leisure time can count as an implicit cost too.
The distinction has a practical edge. OpenStax says accounting profit is a cash concept, and it's the figure a business pays income tax on. Whether the business is a success in economic terms depends on economic profit. Plenty of owners look only at the first number.
CFI's oil field: the same idea at a much bigger scale
CFI uses a deliberately huge example. A firm finds oil on its land. A surveyor says the land could be sold for $40 billion. Extracting the oil would bring in $80 billion in present value, if the firm invests $30 billion today. Accounting profit is $80 billion minus $30 billion, which is $50 billion. But the economic profit is only $10 billion, because the firm gives up the $40 billion it could have had by selling the land. The scale is CFI's illustration, as of October 2026; the logic works exactly the same for a market stall.
How finance teams build it into a decision
In financial analysis, CFI says opportunity cost is factored in through net present value (NPV). When options are mutually exclusive, the rule is to pick the one with the highest NPV. If the alternative gives a single immediate benefit, you can add that benefit to the costs of the project, and the rule becomes: go ahead if NPV is greater than zero.
You don't need a finance degree to use the idea. You need to write the alternative down and put a value on it before you decide, not after.
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Why sunk costs stay out of the sum
There's one cost you should leave out entirely. CFI says a sunk cost has already happened, can't be changed by anything you decide now, and should be ignored. In its oil example, the firm has spent $30 billion when expected revenue drops to $50 billion. Selling the land would bring $40 billion. It carries on, because $50 billion beats $40 billion, and the $30 billion is gone whichever way it goes. Sunk costs are a topic in their own right, and they're the opposite of opportunity cost: one is gone, the other is what you're about to give up.
How to work out opportunity cost in six steps
- List every realistic alternative, including doing nothing.
- Put a value on the best alternative you'd give up, in cash, time or resources.
- Add the explicit costs of the option you're choosing.
- Add the implicit costs: your own unpaid time and any salary you'd forgo.
- Ignore sunk costs, because they're the same whichever way you go.
- Choose the option with the larger net benefit.
If you'd like a wider framework for this, my guide on making informed financial decisions for your business walks through the rest of the process, and these five decisions to make before starting a business are where opportunity cost bites hardest, before you've spent anything.
Where I come in
For most small businesses and SaaS marketing teams, the scarcest resource isn't budget, it's time. Every channel you say yes to is a channel you can't give your full attention to. I've spent 23 years in marketing, and a big part of what I do is help teams decide where their marketing time and budget will earn the most, and what to stop doing so that can happen. You can see how I work on my work with me page.
My verdict
Every yes is a no to something else, and in a one-person business the something else is usually your own time. So put a value on your hours before you take on a low-paying job. If Eryn's numbers teach anything, it's that a business can look profitable and still leave you worse off than the job you left. That's fine if you've chosen it with your eyes open. It's not fine if you never did the sum.
Frequently asked questions
What is opportunity cost in simple terms?
It's the value of the next best option you give up when you choose. CFI describes it as the cost of what else you could have chosen to do.
What's an example of opportunity cost in business?
In OpenStax's example, a lawyer who leaves a $125,000 salary to run a practice making $115,000 in accounting profit has an economic profit of minus $10,000 a year.
What is the difference between explicit and implicit costs?
Explicit costs are out-of-pocket payments such as rent and wages. Implicit costs are the opportunity cost of resources you already own, such as your unpaid time.
Is opportunity cost always measured in cash?
No. OpenStax says it's often more useful to think in time or in the resources you give up.
Should sunk costs be part of an opportunity cost decision?
No. CFI says sunk costs have already happened, can't be changed and should be ignored.
