Why firms earn zero economic profit in the long run
"In the long run, firms in perfect competition earn zero profit." Read that for the first time and it sounds like a business plan for going broke. Why would anyone grow strawberries for nothing? The sentence is right, but two words in it are doing all the work: economic and long run. Once you see what they mean, the zero stops being strange and starts being obvious.
"Zero" is not what it sounds like
Economists count costs differently from an accountant. The accountant adds up the bills: rent, wages, seeds. The economist also counts what the owner gives up by running the farm instead of doing something else: the pay from another job, the interest the money could have earned. That is the opportunity cost of Lesson 1, applied to the owner's own time and money. Economic profit is what is left after all of that. So a farm with zero economic profit is not a farm that pays nothing. It pays its owner exactly what they could have earned in their next best option, no more.
Lesson 6's farmer, Mateo, has his costs counted that way. Keep it in mind as his profit falls to zero.
Start with a profit
Mateo grows strawberries on a small farm, one of thousands selling the same berries. He is a price taker: the market sets the price, $14 a crate, and he only chooses how many crates to grow. His land costs $100 a day whatever he grows, and each batch of ten crates costs more than the one before once the farm gets crowded. At $14, here is what each quantity earns him:
| Crates a day | Revenue at $14 | Total cost | Profit |
|---|---|---|---|
| 60 | $840 | $660 | $180 |
| 70 | $980 | $730 | $250 |
| 80 | $1,120 | $820 | $300 |
| 90 | $1,260 | $940 | $320 |
| 100 | $1,400 | $1,100 | $300 |
His best choice is 90 crates, for $320 a day above every cost, his own time included. But everyone can see the price of strawberries, anyone can plant them, and a crate of berries is a crate of berries. So $320 a day is not only a profit. It is an invitation.
Entry pushes the price down
Each new farm adds its crates to the market's supply, so the whole supply curve shifts to the right. Demand has not changed, so the new crossing with demand sits lower: a lower price for every farm, Mateo's included. Move the slider to let farms in, and watch what the price does to Mateo's best profit.
At $12 Mateo still clears $140 a day, so farms keep arriving. At $11, $60. At $10.25 his best quantity, 80 crates, brings in 80 × $10.25 = $820, and 80 crates cost him exactly $820. Profit: zero. Nobody outside the market sees a reason to join, nobody inside sees a reason to leave, and the price stops moving. That is the long-run equilibrium: "long run" because it takes time to start a farm or close one.
Why it stops exactly at the bottom of ATC
The price did not stop at a random number. $10.25 is the lowest point of Mateo's average total cost (ATC, the cost of one crate with the rent spread over all the crates). Here is why it has to be. Profit is (price − ATC) × crates: a block between the price line and the ATC curve. The block is zero only when the price line touches the ATC curve. And a price-taking firm picks the quantity where marginal cost equals the price, so the touch happens where MC meets ATC, which, as the average rule says, is at ATC's minimum. Slide the price down and watch the block shrink.
Notice that $10.25 is the only price at which the block disappears: above it there is a profit block and entry, below it a loss block and exit.
Losses work the same way, in reverse
Suppose a glut pushes the price to $9.50. Mateo's best is still 80 crates, now for 80 × $9.50 = $760 against $820 of cost: a loss of $60 a day, for him and for every farm like his. Some owners let their lease run out and do something else. Each one that leaves takes its crates out of the market's supply, the supply curve shifts left, and the price rises. It stops rising at the same place it stopped falling: $10.25, where the remaining farms break even. Profit attracts entry, losses cause exit, and both roads lead to the bottom of ATC.
The trap on tests
- Zero economic profit is not zero income. It means every cost is covered, including the owner's own time and money. Economists call it a normal profit, and it is enough to keep every farm in business.
- Shutdown and exit are different decisions. Shutting down is short run: stop growing while the rent is still owed, when the price falls below the minimum of average variable cost ($9 for Mateo). Exiting is long run: leave the market for good, when the price stays below the minimum of ATC ($10.25). Between $9 and $10.25, Mateo grows at a loss and waits.
- The long-run price is at the bottom of ATC, not of MC. Entry stops where price equals the lowest average total cost. Marginal cost is only there because the firm chooses its quantity on the MC curve.
- It takes free entry. The whole argument rests on newcomers being able to join. Where a license, a patent or a huge setup cost keeps them out, profit can last. That is the next lesson, on monopoly.
Quick check
1. The price is $11. Mateo grows 80 crates: revenue $880, cost $820, profit $60. What happens in the long run?
New farms enter, market supply shifts right, and the price falls until the profit is gone: at $10.25, the lowest point of ATC, where 80 crates bring in exactly what they cost.
2. Mateo's land rent rises from $100 to $160 a day, for every farm. Where does the long-run price end up?
Higher. The extra $60 is a fixed cost, so every total cost in the table rises by $60 and ATC rises: at 80 crates it is now $880 ÷ 80 = $11.00, still the lowest point. At $10.25 every farm would lose $60, farms exit, and the price rises to $11.00, where profit is zero again.
3. True or false: "In long-run equilibrium, strawberry farmers earn nothing."
False. They earn zero economic profit: the price covers rent, wages, seeds and what the owner could have earned elsewhere. The farm pays its owner as much as their next best option, which is exactly why they stay.