CFA Level I Exam · Capital Flows and the FX Market

Real Exchange Rates, Marshall-Lerner and Currency Crises

Updated 7 October 2026 · Fact-checked

The real exchange rate adjusts the nominal rate for price levels: real = nominal (domestic per foreign) × P foreign ÷ P domestic. A depreciation improves the trade balance if import and export demand elasticities sum to more than 1 (Marshall-Lerner), though the J-curve can delay this. Crises show warning signs such as reserve losses and large deficits.

Understand Real Exchange Rates and Currency Crises

A nominal exchange rate is the price of one currency in another. It says nothing about what the money buys. The real exchange rate adjusts for price levels in both countries, so it measures relative purchasing power and competitiveness.

Quote the rate as domestic currency per unit of foreign currency (d/f). Then the real rate = nominal S(d/f) × CPI foreign ÷ CPI domestic. A higher real rate means foreign goods are more expensive relative to domestic goods, so the domestic currency has depreciated in real terms. If you hold the nominal rate fixed and domestic inflation exceeds foreign inflation, the real rate falls: domestic goods get dearer, and the domestic currency has appreciated in real terms.

The Marshall-Lerner condition asks whether a real depreciation improves the trade balance. A depreciation makes imports cost more in domestic currency and makes exports cheaper abroad. With sticky prices, a nominal depreciation is also a real depreciation, so the condition applies to that real depreciation. Volumes adjust, but values depend on how strongly. The trade balance improves if the sum of the absolute price elasticities of export demand and import demand is greater than 1. This simple sum form assumes trade starts roughly balanced. With an initial deficit, a weighted version of the condition applies, where the elasticities are weighted by the relative size of exports and imports.

The J-curve describes timing. In the short run, contracts are fixed and volumes barely move, but the domestic price of imports jumps. The trade balance worsens first. Later, as volumes respond, it improves and traces a J shape, provided the Marshall-Lerner condition holds in the long run.

Currency crises are sharp falls in a currency, often after a fixed or managed rate breaks. Common warning signs: rapidly falling foreign exchange reserves, a large and persistent current account deficit, a real exchange rate that has appreciated well above trend, fast credit growth, heavy short-term foreign-currency borrowing, rising inflation, and a large fiscal deficit. A sudden stop of capital inflows often triggers the crash. No single indicator is reliable on its own.

Key formulas to remember

Real exchange rate (d/f): Real S(d/f) = S(d/f) × (CPI foreign ÷ CPI domestic); Use the same quote direction as the nominal rate. Higher value = real depreciation of the domestic currency.
Change in real rate (approximate): % change in real rate ≈ % change in nominal (d/f) + foreign inflation − domestic inflation; Approximation for small changes. Use the exact formula when options are close.
Marshall-Lerner condition: |ε exports| + |ε imports| > 1; ε = price elasticity of demand. Applies when trade is roughly balanced at the start. Sum above 1 means depreciation improves the trade balance.
J-curve pattern: Short run: trade balance worsens. Long run: it improves if Marshall-Lerner holds.; Reason: volumes are slow to adjust, but import prices rise at once.
Crisis warning signs: Falling reserves, large current account deficit, overvalued real rate, rapid credit growth, short-term foreign debt; Indicators, not guarantees. Know the list and the direction of each.

How to solve Real Exchange Rates and Currency Crises questions

Use this order for any question on real rates, elasticity, J-curve or crises.

1Identify the quote convention. Confirm the rate is domestic per foreign (d/f). If it is f/d, invert it first.
2For a real rate, put the foreign price index in the numerator and the domestic price index in the denominator when using d/f.
3Compute the real rate at each date, or use the approximation for percentage changes. Compare the two.
4Interpret direction: a higher d/f real rate is a real depreciation of the domestic currency; a lower one is a real appreciation.
5For trade balance questions, add the absolute elasticities. Above 1 means a depreciation improves the balance; below 1 means it worsens it.
6For timing questions, ask whether the horizon is short run (J-curve dip) or long run (improvement).
7For crisis questions, match the scenario to the warning signs: reserves, current account, real appreciation, credit growth, short-term foreign debt.
8Eliminate the two options that reverse direction or misstate the condition, then check arithmetic on the survivor.

Quickest way: Direction-first elimination

When to use it: Use for conceptual and direction questions, or when numerical options differ clearly.

Decide the direction before calculating. If domestic inflation is higher than foreign and the nominal rate is unchanged, the domestic currency appreciates in real terms.
For d/f rates, add foreign inflation and subtract domestic inflation to the nominal change for a fast estimate.
Strike any option with the wrong sign. Options run smallest to largest, so check where the estimate falls.
For Marshall-Lerner, just add the two elasticities and compare with 1.
For the J-curve, pick 'worsens first, improves later' unless the question says the condition fails.

Common mistakes in Real Exchange Rates and Currency Crises

Putting the domestic price index in the numerator of the real rate for a d/f quote.
Students memorise the formula without linking it to the quote direction.
Fix: With d/f, foreign CPI goes on top. Sanity check: higher foreign prices should raise the real d/f rate.
Treating a higher d/f rate as an appreciation of the domestic currency.
A bigger number feels like a stronger currency.
Fix: A d/f rate is the price of foreign currency. Higher means more domestic currency per foreign unit, so the domestic currency has depreciated.
Using the Marshall-Lerner condition as 'each elasticity must exceed 1'.
Students recall only 'greater than 1'.
Fix: It is the sum of the absolute elasticities of export and import demand that must exceed 1.
Saying depreciation always improves the trade balance immediately.
Ignoring the time lag in volume adjustment.
Fix: In the short run the balance can worsen (J-curve). Improvement needs time and a sum of elasticities above 1.
Applying the Marshall-Lerner condition to a nominal depreciation without checking that it is also a real depreciation.
Textbooks say 'depreciation' loosely, so nominal and real moves get blurred.
Fix: The condition concerns how a real depreciation affects the trade balance. With sticky prices, a nominal depreciation is also a real depreciation, so the condition applies to it. If domestic prices rise enough to offset the nominal fall, there is no real depreciation and no lasting trade effect.
Naming a single warning sign as proof of an imminent crisis.
Students over-read rules of thumb.
Fix: Warning signs are indicators that raise risk. Choose the option that lists a combination consistent with vulnerability.

Worked examples

Example 1

The nominal exchange rate is 0.80 EUR/USD (EUR per USD, domestic = EUR) at Time 0 and 0.84 at Time 1. Over the period, US prices rise 2.0% and euro-area prices rise 1.0%. Which is closest to the percentage change in the real exchange rate (EUR/USD), and what does it indicate? A) −3.0%, real appreciation of the euro B) +1.0%, real depreciation of the euro C) +6.0%, real depreciation of the euro

Show the solution

Nominal change = 0.84 ÷ 0.80 − 1 = +5.0%.
Foreign (US) inflation is 2.0%; domestic (euro-area) inflation is 1.0%.
Approximate real change = 5.0% + 2.0% − 1.0% = +6.0%.
Exact check: 1.05 × 1.02 ÷ 1.01 = 1.0604, so +6.04%.
A higher EUR/USD real rate means more EUR needed per unit of US basket value: the euro depreciated in real terms. Option A has the wrong sign, and option B has the right direction but the wrong size.

Answer: C. About +6.0%, a real depreciation of the euro.

Example 2

A country's export demand has a price elasticity of 0.4 and import demand has a price elasticity of 0.5 (absolute values). Trade is roughly balanced. Its currency depreciates. Which statement is most accurate about the long-run effect on the trade balance? A) The trade balance will worsen in the long run because the sum of elasticities is below 1 B) The trade balance will improve in the long run because the sum of elasticities exceeds 1 C) The trade balance will improve immediately because import prices rise

Show the solution

Sum of absolute elasticities = 0.4 + 0.5 = 0.9.
Marshall-Lerner requires a sum above 1. 0.9 is below 1, so the condition fails.
Because it fails, depreciation does not improve the trade balance even in the long run. The J-curve recovery does not apply.
Option B is wrong because the sum is not above 1.
Option C is wrong because higher import prices do not improve the balance when volumes respond too little; with a sum below 1 the balance worsens.
Option A matches the result.

Answer: A. The condition fails, so the trade balance worsens in the long run.

Exam tips

Always write the quote direction (d/f) beside the formula before computing. Most lost marks come from inverted rates.
Questions often hide the answer in the word 'real'. Check whether inflation differentials change the conclusion.
For Marshall-Lerner, add the elasticities and compare with 1. It takes ten seconds.
For crisis questions, pick the option with several linked vulnerabilities such as falling reserves plus a large deficit plus fast credit growth.
With no penalty for wrong answers, never leave a blank. Eliminate the option with the wrong direction first.

Practice questions from Capital Flows and the FX Market

Real Exchange Rates and Currency Crises: frequently asked questions

What is the real exchange rate formula for CFA Level I?

For a domestic-per-foreign quote, real rate = nominal rate × (foreign price level ÷ domestic price level). Use the approximation that the real change is the nominal change plus foreign inflation minus domestic inflation. Always check the quote direction first.

What is the Marshall-Lerner condition in simple terms?

It says a currency depreciation improves the trade balance if the sum of the absolute price elasticities of export demand and import demand is greater than 1. It assumes trade starts roughly balanced. If the sum is below 1, the balance worsens.

Why does the J-curve happen after depreciation?

In the short run, import and export volumes are fixed by existing contracts and habits, but imports cost more in domestic currency, so the balance worsens. As volumes adjust, the balance can improve. That recovery needs the Marshall-Lerner condition to hold.

What are the main currency crisis warning signs?

Falling foreign exchange reserves, a large current account deficit, a real exchange rate that has appreciated strongly, rapid credit growth, and heavy short-term foreign-currency debt. A sudden stop in capital inflows often triggers the crisis. No single sign is conclusive.