International Capital Flows and Equilibrium

Core Idea

International capital flows are motivated by interest rate differentials and risk considerations. Capital flows adjust to equalize risk-adjusted returns across countries. Equilibrium requires expected return on domestic assets equals expected return on foreign assets (adjusted for exchange risk).

How It's Best Learned

Set up uncovered interest rate parity: r_domestic ≈ r_foreign + expected depreciation. Show if US rate exceeds German, investors expect dollar depreciation. If not, capital flows to US until returns equalize.

Common Misconceptions

• Assuming capital flows respond instantly.
• Treating interest rate parity as a law.
• Forgetting expectations matter.

Explainer

From your work on the current account, you know that a country's external position reflects how much it's borrowing from or lending to the rest of the world. The capital account (or financial account) is the flip side: every dollar borrowed must have a corresponding capital inflow, and every dollar lent out corresponds to a capital outflow. What determines which direction capital flows? In a world of mobile capital, the answer is relative returns — adjusted for risk and expected exchange rate movements.

The fundamental equilibrium condition is uncovered interest rate parity (UIP): in equilibrium, the expected return on domestic assets must equal the expected return on foreign assets, once you account for expected exchange rate changes. If the US interest rate is 5% and the German rate is 2%, the gap doesn't persist as a free lunch. Investors will rush to US assets, buying dollars and selling euros. This drives the dollar up — and because an appreciated dollar is expected to depreciate back toward fundamentals over time, that expected depreciation is exactly the 3% gap. Equilibrium is reached when: r_domestic ≈ r_foreign + expected depreciation of domestic currency.

The dynamics of adjustment are crucial to understand. When the US rate rises relative to Germany's, capital initially flows *to* the US — investors sell euros, buy dollars, and purchase US bonds. This flow appreciates the dollar immediately (the "overshooting" phenomenon). The dollar has now appreciated *past* its long-run equilibrium, so it's expected to depreciate going forward, which is precisely what makes US and German assets equally attractive again. The equilibrium isn't that capital flows stop — it's that the exchange rate has moved enough to make the expected returns equal, so there's no further incentive for net flows.

In practice, several things complicate this clean picture. Capital flows are lumpy, not continuous: institutional investors rebalance periodically, creating discrete adjustment episodes rather than smooth convergence. Risk premiums matter — a country with default risk or political instability must offer higher interest rates just to attract the same capital, even after adjusting for expected depreciation. Capital controls in emerging markets can sever the parity condition entirely for periods of time. And expectations are endogenous: if investors believe a currency will depreciate, they demand a premium that can make that belief self-fulfilling. Understanding capital flow equilibrium means holding all these moving parts together: interest rates, exchange rates, expectations, and the risk environment all interact simultaneously.