A tariff looks like a tax on foreigners. It is mostly a tax on your own consumers. Taking the trade pattern as given, this page asks what taxing or capping imports does to national welfare — the topic that most often brings intermediate students to economics tutors in Singapore. Four small areas on one diagram are the whole of it.
1 · The small open economy, and why the world price binds
Take one market inside a trading country — steel. Domestic buyers have a demand curve, domestic firms a supply curve; left alone they clear at the autarky price, where the two curves cross.
Now open the border. The country is small: it cannot move the world price, so it faces a flat world supply at a fixed Pw. If Pw lies below the autarky price, buyers want more than domestic firms supply, and imports fill the gap between the two curves at Pw. Why those imports exist — the comparative-advantage reason another country makes steel more cheaply — is its own lesson; here the pattern is given.
2 · A tariff, and the four areas it creates
Impose a specific tariff t, a fixed charge per tonne imported. The country is small, so the world price holds and the domestic price rises by the full tariff, to Pw + t. Domestic supply rises, demand falls, imports shrink.
Four areas open between the old and new price lines:
- Area a — producers earn the higher price on every unit they make: a transfer from consumers to domestic firms, not a national loss.
- Area c — the government collects t on each imported unit: revenue, another transfer.
- Areas b and d — nobody receives these; they are the country’s deadweight loss.
b is the production distortion: the extra home tonnes cost more to make than to buy at the world price, so real resources are wasted. d is the consumption distortion: buyers priced out valued those tonnes above the world price, so beneficial trades never happen. Consumers lose a + b + c + d, but only b + d leaves the economy.
3 · Quotas, quota rents, and the equivalence that half-holds
A quota caps imported tonnes. Set the cap at the volume a given tariff would have allowed, and the domestic price climbs to the same Pw + t — same a, b, d. On the picture the two are identical.
One area differs, and it decides the verdict. Under the tariff, c is revenue. Under the quota, c is a rent earned by whoever holds the import licence. Auction the licences and the government captures c, so the two are welfare-equivalent; hand them to foreign exporters and c leaves the country, making the national loss b + c + d. Who gets the rent is the whole question.
The equivalence is a special case. It breaks under domestic monopoly, which a quota shelters but a tariff disciplines, and as demand grows, since a tariff fixes the price gap while a quota fixes the volume. It also assumes a small country: a large importer can push the world price down by buying less — the terms-of-trade or “optimum tariff” argument — but that is beyond this page.
4 · Do the arguments for protection survive?
Infant industry. A young sector above world cost today may fall below it at scale, so a temporary tariff buys time to grow. But if the future profits are real, private capital should fund the wait — and “temporary” tariffs rarely die.
Anti-dumping. A tariff can be defended as blocking a foreign firm that prices below cost to kill rivals. But genuine predation is rare and hard to recoup against imports; most anti-dumping duties just punish low prices that help domestic buyers.
Neither case is empty. Both are narrower than the rhetoric that invokes them.
Worked example — a stylised steel importer
Work in £ thousand (a price in £ per tonne times a quantity in thousand tonnes). Domestic demand is Qd = 100 − P, supply Qs = P − 20, the world price Pw = 40, the tariff t = 10.
Step 1 — Autarky. Set Qd = Qs: 100 − P = P − 20, so P = 60. Since 40 < 60, the world price binds and the country imports.
Step 2 — Free trade. At P = 40, Qs = 20 and Qd = 60. Imports are the gap, 40.
Step 3 — The tariff bites. The domestic price rises to Pw + t = 50. Now Qs = 30 and Qd = 50, so imports fall to 20 — cut in half.
Step 4 — The transfers. Producer gain a = ½(20 + 30)(10) = 250. Revenue c = 10 × 20 = 200.
Step 5 — The deadweight triangles. b = ½(30 − 20)(10) = 50; d = ½(60 − 50)(10) = 50.
Step 6 — The identity. Consumer loss = ½(60 + 50)(10) = 550, and it splits exactly: 550 = 250 (a) + 200 (c) + 100 (b + d).
Step 7 — Interpret. The tariff moved 250 to producers and 200 to the treasury, but destroyed 100 of surplus to do it. That 100 buys nothing — it is the cost of protecting 10 extra home tonnes and denying 10 to willing buyers.
Could you draw the two price lines, shade all four areas, and say which are transfers and which the country simply loses? Writing the identity a + b + c + d — and defending which pieces leave the economy — is exactly what trade-policy questions reward. A one-on-one economics tutor builds the tariff diagram from the curves with you until the welfare split is automatic. Book a trial session.
Practice
Q1. Another small economy imports wheat: Qd = 120 − P, Qs = P − 40, world price 50, tariff 10. Find imports before and after, government revenue, and the deadweight loss.
Q2. For Q1’s market and tariff, find the import quota that reproduces the tariff’s domestic price. State the national welfare loss if the licences are (a) auctioned, or (b) handed free to foreign exporters.
Answers. Q1: autarky 80, so the world price binds. Imports fall 60 → 40; revenue = 10 × 40 = 400; deadweight loss = 50 + 50 = 100 (the identity: 650 = 150 + 400 + 100). Q2: the quota is the post-tariff volume, 40, which drives the price to 60 — the tariff price. (a) Auctioned, the government keeps the rent 400, so the national loss is 100, identical to the tariff. (b) Given to foreigners, the 400 rent leaves, so the national loss is b + c + d = 500.
Key takeaways
- The domestic price rises by the full tariff in a small open economy — a price-taker cannot shift the world price, and every welfare area follows from that.
- Two of the four areas are transfers, two are losses. Producer gain a and revenue c stay inside the country; the triangles b and d are surplus destroyed.
- The consumer loss splits as a + b + c + d. Writing that identity, and naming which pieces are transfers, is the most-tested skill here.
- A quota matches a tariff on price but not on area c. Auction the licences and it is revenue; give them away and the country loses that rectangle too.
Why Singapore students choose our economics tutoring
- Areas derived, not memorised: sessions build a, b, c and d from the demand and supply curves, so you can reconstruct the welfare split under exam pressure.
- The distinctions examiners test, drilled: transfer versus deadweight loss, tariff versus quota, small versus large country.
- One-on-one and matched to your course: a PhD tutor works from your own notation and past papers, whether your module follows Krugman–Obstfeld, Feenstra, or your lecturer’s own handouts.
FAQ
Q: What exactly is the deadweight loss of a tariff?
A: The two triangles b and d — the production and consumption distortions. They are surplus that disappears rather than moving to producers or the government, so the country is worse off.
Q: Why does the domestic price rise by the whole tariff?
A: Because a small country is a price-taker: it cannot lower the world price by importing less, so the full charge passes into the domestic price.
Q: Is a tariff or a quota worse for consumers?
A: On price they are identical. The difference is where area c goes: to the treasury under a tariff, to whoever holds the licence under a quota.
Q: Who gets the money from an import quota?
A: The licence-holder earns the rent. Auction the licences and the government captures it; give them to foreign exporters and the money leaves the country.
Q: Does the infant-industry argument justify tariffs?
A: Only under strict conditions that private lenders somehow will not finance. Since temporary tariffs prove hard to remove, most economists treat the case cautiously.
Book an economics tutor in Singapore or online
Trade policy rewards students who can draw the tariff diagram from the curves and name every area — transfer or loss — not just say “tariffs are bad.” One-on-one sessions build that fluency on your own past papers, from the welfare identity to the tariff-quota comparison. Tell us your course and exam date, and we will match you with the right tutor this week.
