CFA Level I Exam · International Trade

Gains from Trade and Comparative Advantage Explained

Updated 7 October 2026 · Fact-checked

Comparative advantage means a country can produce a good at a lower opportunity cost than another country. Find each country's opportunity cost for each good, then specialize in the good with the lower cost and trade. Both countries can then consume more than they could alone, even if one has an absolute advantage in everything.

Understand Gains from Trade and Comparative Advantage

Start with a simple idea. A country has an absolute advantage in a good if it can produce it using fewer resources than another country. That means higher output per unit of labor or other inputs. Absolute advantage compares productivity directly.

A country has a comparative advantage in a good if its opportunity cost of producing that good is lower than the other country's. Opportunity cost is what you give up in another good to make one more unit of this good. This is the key idea for the exam. A country can have an absolute advantage in both goods and still have a comparative advantage in only one. Each country is better off specializing where its opportunity cost is lower.

This is why trade creates gains. Without trade, a country can consume only what it produces. With trade, each country specializes in its comparative-advantage good and exchanges it at a price between the two countries' opportunity costs. Each then consumes outside its own production possibility frontier. Total world output rises, and consumers get more variety and lower prices. Gains are not equal for everyone. Within a country, owners of factors tied to the export sector gain, while those tied to the import-competing sector can lose.

The Ricardian model explains comparative advantage by differences in technology, with labor as the only factor of production. Productivity differences across countries give different opportunity costs. The Heckscher-Ohlin model explains it by differences in factor endowments, usually capital and labor. A country exports the good that uses intensively the factor it has in abundance, and imports the good that uses intensively the factor that is scarce. A capital-abundant country exports capital-intensive goods. A labor-abundant country exports labor-intensive goods.

Both models are simple. They assume things like no transport costs and no trade barriers. Real trade also involves economies of scale, product differentiation and trade within the same industry, which these models do not fully explain.

Key formulas to remember

Opportunity cost of good X (in units of Y): Opportunity cost of X = units of Y given up ÷ units of X gained; With labor-hours per unit: OC of X = (hours per unit of X) ÷ (hours per unit of Y). With output per worker: OC of X = (output of Y) ÷ (output of X).
Comparative advantage rule: Country has comparative advantage in X if OC of X (home) < OC of X (partner); Opportunity costs of the two goods are reciprocal. If a country has the lower OC in one good, the other country has it in the other, unless the OCs are equal.
Absolute advantage rule: Absolute advantage in X if fewer inputs per unit of X, or more output per unit of input; Compares productivity only. It does not decide the pattern of trade.
Terms of trade range: OC of X (low-cost country) < trade price of X in Y < OC of X (high-cost country); Both countries gain only if the terms of trade lie strictly between the two opportunity costs.
Heckscher-Ohlin pattern: Export the good intensive in the abundant factor; import the good intensive in the scarce factor; Differences in factor endowments drive trade. Ricardian drivers are technology differences.

How to solve Gains from Trade and Comparative Advantage questions

Use this method for any question on absolute advantage, comparative advantage or trade patterns.

1Identify the data format: output per worker (or per hour) or labor-hours per unit. This decides whether you divide one way or the other.
2Check absolute advantage first if asked: higher output per input, or fewer inputs per unit, wins.
3Compute the opportunity cost of one good in terms of the other for each country. Write it as 'units of Y given up per unit of X'.
4Compare the opportunity costs across countries. The lower OC for a good means comparative advantage in that good.
5State the specialization: each country produces and exports the good where its OC is lower.
6If terms of trade are given, check they lie between the two opportunity costs. If so, both gain; compute consumption or gains if asked.
7For model questions, match the driver: technology differences point to Ricardian; factor endowments point to Heckscher-Ohlin.

Quickest way: Cross-ratio check in three lines

When to use it: Use when you get a two-country, two-good productivity table and need the comparative advantage fast.

Write the data for each country as a pair: (X, Y). Note the format first, because the rule in step 2 depends on it.
If the data is output per worker, compute the ratio X ÷ Y for each country. The country with the higher ratio is relatively better at X, so it has comparative advantage in X. If the data is labor-hours per unit, the rule works the other way: the country with the lower hours ratio (X hours ÷ Y hours) has comparative advantage in X.
The other country has comparative advantage in Y. Pick the option that matches, and ignore options that confuse this with absolute advantage.

Common mistakes in Gains from Trade and Comparative Advantage

Treating absolute advantage as the basis for trade
It feels natural that the more productive country should produce everything.
Fix: Always convert to opportunity cost. Trade is based on comparative advantage, and a country with an absolute advantage in both goods still gains by trading.
Dividing the wrong way when computing opportunity cost
Data given as 'output per worker' and 'hours per unit' need opposite handling.
Fix: Ask what is given up. With output per worker, OC of X = output of Y ÷ output of X. With hours per unit, OC of X = hours for X ÷ hours for Y.
Believing one country can have comparative advantage in both goods
Confusing it with absolute advantage.
Fix: Opportunity costs are reciprocal. If your OC of X is lower, your OC of Y is higher, so advantage is split between countries.
Mixing up Ricardian and Heckscher-Ohlin drivers
Both models give comparative advantage as the result, so the names blur.
Fix: Ricardian equals technology (labor productivity). Heckscher-Ohlin equals factor endowments (capital versus labor abundance).
Saying everyone in a country gains from trade
The headline result is that the country as a whole gains.
Fix: Trade raises national welfare, but owners of the abundant factor gain and owners of the scarce factor can lose. Gainers could compensate losers in principle.
Choosing terms of trade outside the opportunity-cost range
Students check only one country's cost.
Fix: Test the price against both countries' opportunity costs. It must be between them for both to gain.

Worked examples

Example 1

In one day a worker in Country A can make 6 units of wheat or 12 units of cloth. A worker in Country B can make 2 units of wheat or 8 units of cloth. Which statement is correct? A) B has a comparative advantage in wheat. B) A has a comparative advantage in cloth. C) A has a comparative advantage in wheat.

Show the solution

Absolute advantage: A is better at both goods (6 > 2 wheat; 12 > 8 cloth).
Opportunity cost of 1 wheat in A = 12 ÷ 6 = 2 cloth.
Opportunity cost of 1 wheat in B = 8 ÷ 2 = 4 cloth.
A has the lower opportunity cost of wheat, so A has comparative advantage in wheat.
Check cloth: OC of 1 cloth in A = 6 ÷ 12 = 0.5 wheat; in B = 2 ÷ 8 = 0.25 wheat. B has the lower cost, so B has comparative advantage in cloth.
Option A is false, option B is false, option C is true.

Answer: C. A has a comparative advantage in wheat, even though it has an absolute advantage in both goods.

Example 2

Producing one tonne of steel takes 4 labor-hours in Country X and 6 labor-hours in Country Y. Producing one tonne of grain takes 2 labor-hours in X and 5 labor-hours in Y. Which price of 1 tonne of steel, in tonnes of grain, would let both countries gain from trade? A) 0.8 B) 1.7 C) 2.6

Show the solution

Opportunity cost of 1 steel in X = 4 ÷ 2 = 2 grain.
Opportunity cost of 1 steel in Y = 6 ÷ 5 = 1.2 grain.
Y has the lower OC of steel, so Y exports steel and X exports grain.
For both to gain, the price of steel must lie between 1.2 and 2.0 grain.
0.8 is below 1.2, so Y would not sell steel for it. 2.6 is above 2.0, so X would rather make its own steel. 1.7 lies in the range.

Answer: B. A price of 1.7 tonnes of grain per tonne of steel lies between 1.2 and 2.0, so both countries gain.

Exam tips

Questions give a productivity table and ask who has comparative advantage. Compute opportunity cost for one good only, then reason by reciprocity for the other.
Watch the wording. 'Absolute advantage' is a direct productivity comparison, and an option may be correct on that basis but wrong on comparative advantage.
For Ricardian versus Heckscher-Ohlin, look for the keyword: technology or labor productivity means Ricardian; capital, labor or land abundance means Heckscher-Ohlin.
If the terms of trade are listed as options, eliminate any that sit outside the two opportunity costs. That usually leaves one choice.
With three options and no penalty, never leave a blank. Eliminate the option that claims one country has comparative advantage in both goods.

Practice questions from International Trade

Gains from Trade and Comparative Advantage in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Actuarial Core Principles (IAI)Absolute and Comparative Advantage

Gains from Trade and Comparative Advantage: frequently asked questions

What is the difference between absolute and comparative advantage?

Absolute advantage means producing a good with fewer resources than another country. Comparative advantage means producing it at a lower opportunity cost. A country can have an absolute advantage in everything but a comparative advantage in only some goods.

How do I calculate opportunity cost for comparative advantage?

Work out how much of the other good is given up for one unit of this good. With output per worker, divide the other good's output by this good's output. With labor-hours per unit, divide this good's hours by the other good's hours. Then compare across countries.

What is the difference between the Ricardian and Heckscher-Ohlin models?

The Ricardian model says comparative advantage comes from differences in technology or labor productivity. The Heckscher-Ohlin model says it comes from differences in factor endowments, such as capital and labor. In Heckscher-Ohlin, a country exports the good that is intensive in its abundant factor.

Do all people in a country gain from trade?

The country gains overall, with higher total consumption possibilities. But gains are uneven. Owners of the abundant factor tend to gain and owners of the scarce factor can lose, so the gains are shared unevenly within the country.