Opportunity cost is the value of the best thing you did not do. Enter the amount, the time period, and the annual return of the option you are taking alongside the one you are giving up, and the calculator shows where each one ends and what the gap between them is worth.
Set the first return to zero and it answers the simplest version of the question: what does spending this money now cost me compared with putting it to work? Open the optional section to take tax off the gain and convert the answer back into today's money.
What opportunity cost actually measures
Every decision to use money, time, or attention on one thing is simultaneously a decision not to use it on everything else. Opportunity cost is the value of the best of those alternatives.
The word "best" is doing the work. Opportunity cost is not the sum of everything you could have done, and it is not a vague sense of missed chances. It is one number: what the single strongest alternative would have produced. That precision is what makes it usable.
It also never appears in your accounts. No ledger records the return you did not earn, which is exactly why the concept exists. Accounting profit measures what happened. Economic profit subtracts what would have happened otherwise, and it is the harder and more honest measure.
The opportunity cost formula
Opportunity cost = Value of the best alternative − Value of the option chosen
When the comparison is between two investments held over the same period, each side compounds:
Future value = Amount × (1 + Rate ÷ n)^(n × Years)
Where n is the number of compounding periods per year.
Then, if you want the after-tax and real figure rather than the nominal one:
After tax = Amount + (Gain × (1 − Tax rate))
In today's money = After-tax value ÷ (1 + Inflation)^Years
Tax applies only to the gain, not to the capital you started with. Inflation applies to the whole ending amount, because the question it answers is what that sum will actually buy.
Two worked examples
Choosing between two uses of capital. You have $250,000. You can put it into a project you expect to return 6% a year, or into an alternative returning 11%. The horizon is three years.
Your option = $250,000 × 1.06³ = $297,754
Alternative = $250,000 × 1.11³ = $341,908
Opportunity cost = $44,154
The project is profitable. It also costs you $44,154 relative to the thing you could have done instead, and that number will appear in no report anyone writes about it.
Spending now against investing. A $15,000 purchase you could defer for two years, against an account returning 3% compounded monthly.
Alternative = $15,000 × (1 + 0.03 ÷ 12)^24 = $15,926.36
Opportunity cost = $926.36
Add a 22% tax on the gain and 1.5% annual inflation and the picture changes again. Tax takes $203.80, leaving $15,722.56. Discounting two years of inflation gives $15,261.29 in today's money, so the real opportunity cost is $261.29 rather than $926.36. Most of what looked like a gain was the currency losing value and the tax authority taking a share.
Why the alternative you pick decides everything
The formula is trivial. Choosing what goes on the other side of it is the entire exercise.
The correct comparison is the best available alternative, which for a business is usually one of three things:
The cost of capital. If money is not deployed here, it services debt or is returned to shareholders. Weighted average cost of capital is the floor.
The next project on the list. If you have more good ideas than funding, the opportunity cost of any project is the best one it displaces.
A risk-adjusted market return. For genuinely idle capital, what a passive investment of comparable risk would have earned.
The most common error is comparing an ambitious project against doing nothing, which flatters everything. If your alternative return is zero, you have decided the money had no other use, and that is almost never true.
The second most common is comparing returns of different risk. A 15% expected return from a speculative project and an 11% expected return from a safe one are not directly comparable, and adjusting for risk before comparing is not optional.
Opportunity cost outside money
The calculator handles capital, but the concept extends further, and for most operators the non-cash versions matter more.
Engineering time. A quarter spent on one feature is a quarter not spent on the next best one. This is the largest and least measured opportunity cost in most software businesses.
Management attention. The scarcest resource in any growing company. A leader running one initiative is not running another.
Balance sheet capacity. Debt taken for one purpose is debt unavailable for another, which is why lines of credit have an opportunity cost even when undrawn.
Positioning. Choosing to serve one segment is choosing not to serve another well, and reversing that decision takes years.
In each case the arithmetic is unavailable and the discipline still applies: name the best alternative explicitly, before deciding, rather than after.
Where opportunity cost misleads
The alternative is hypothetical. You are comparing a real decision against an estimate of something that never happened, and estimates of paths not taken are unusually flattering.
Sunk costs contaminate it. Money already spent belongs in neither side of the comparison. What matters is only what each option produces from here.
It ignores risk unless you make it. Two returns are not comparable until both are adjusted for the chance of not getting them.
It ignores optionality and learning. A project with a lower expected return that teaches the organisation something, or opens a door, is worth more than its cash flows suggest.
It can paralyse. Every choice has an opportunity cost. Applied to everything, the concept becomes a reason never to commit. It is a tool for material decisions, not for all of them.
Opportunity cost, sunk cost, and economic profit
Concept | What it refers to | What to do with it |
|---|---|---|
Opportunity cost | The value of the best alternative forgone | Include it in every material decision |
Sunk cost | Money already spent and unrecoverable | Ignore it entirely |
Economic profit | Accounting profit minus opportunity cost | The honest measure of whether a choice created value |
Hurdle rate | The minimum return that clears the alternative | The practical expression of opportunity cost |
Economic profit is where this becomes concrete. A business earning 8% on capital that costs 11% is reporting a profit and destroying value, and the only metric that shows it is the one that subtracts the alternative.
How operators actually use it
Name the alternative before you decide, in writing. The discipline is not the arithmetic, it is being forced to state what else the money could do.
Use your cost of capital as the default floor. Nothing should be approved below it, because below it the capital was better used elsewhere by definition.
Rank the whole list, then fund downwards. Opportunity cost only becomes visible when projects compete against each other rather than against approval.
Apply it to time as seriously as to money. For most companies the binding constraint is engineering and management capacity, not cash.
Revisit it when the alternatives change. A project approved when the alternative returned 3% may not survive a world where the alternative returns 9%.
Further reading from Revenue Memo
FAQs
How do I calculate opportunity cost?
Work out what the option you are choosing will be worth at the end of the period, do the same for the best alternative, and subtract one from the other. Putting $250,000 into a 6% project instead of an 11% one for three years costs $44,154.
What is a simple example of opportunity cost?
Spending $15,000 today rather than investing it at 3% for two years. The investment would have grown to $15,926, so the opportunity cost of the purchase is $926 before tax and inflation.
Is opportunity cost the same as sunk cost?
No, and they are opposites in how you should treat them. Opportunity cost is about the future and belongs in every decision. Sunk cost is money already spent that cannot be recovered, and it should be excluded entirely.
Should opportunity cost include inflation and tax?
For any comparison over more than a year or two, yes. Tax reduces the gain you actually keep, and inflation reduces what the ending sum will buy. The calculator above applies tax to the gain and then converts the result into today's money.
What is the opportunity cost of capital?
The return your capital could earn in its next best use of comparable risk. For most businesses this is the weighted average cost of capital, and it is the floor any investment has to clear before it is worth making.
Does opportunity cost appear in financial statements?
No. Accounts record what was spent and earned, not what could have been. This is precisely why economic profit, which subtracts opportunity cost from accounting profit, gives a different and usually less flattering answer.
How do I choose the right alternative to compare against?
Use the single best option genuinely available to you, adjusted for risk. That is usually your cost of capital, the next project on your funding list, or a comparable market return. Comparing against doing nothing sets the bar at zero and makes every decision look good.