BP Curve and Balance of Payments Quiz: External Balance

The BP curve represents all combinations of national income and the interest rate at which the balance of payments is in equilibrium. At each point on the curve, the current account deficit or surplus is exactly offset by an equal and opposite capital account flow. Higher income increases imports and worsens the current account, requiring a higher interest rate to attract the capital inflows needed to maintain overall balance of payments equilibrium.

The answer is True. As domestic income rises, spending on imports increases, which worsens the current account. To keep the overall balance of payments in equilibrium, the capital account must improve by an equal amount. A higher domestic interest rate attracts capital inflows from abroad, improving the capital account. The need to raise the interest rate every time income rises gives the BP curve its positive upward slope in the income and interest rate space.

With very high capital mobility, even a small difference between the domestic and world interest rate triggers massive capital flows. This means the balance of payments can be maintained at the world interest rate across a wide range of income levels, making the BP curve nearly horizontal. Under perfect capital mobility, the BP curve is completely flat at the world interest rate, which is the key assumption used in the Mundell Fleming model to derive its policy effectiveness conclusions.

The BP curve shifts rightward when the current account improves independently of income and the interest rate. This occurs when foreign income rises and increases demand for domestic exports, or when the domestic currency depreciates and makes exports cheaper. At every combination of income and the interest rate, the balance of payments is now in surplus, meaning the economy can support a higher level of income without needing a higher interest rate to attract equilibrating capital inflows.

The BP curve slopes upward for the reason described. Points above the BP curve represent a surplus because the interest rate is higher than needed to offset the current account deficit at that income level, attracting excess capital inflows. Points below the BP curve represent a deficit. The curve shifts rightward when net exports improve. The claim that points below the curve represent a surplus is incorrect; points below represent a balance of payments deficit.

The answer is True. When capital mobility is zero, no financial capital crosses borders regardless of interest rate differences. The balance of payments is then determined entirely by the current account, specifically trade flows. Since the current account depends on income but not on the interest rate, the BP curve becomes vertical. This means only one level of income is consistent with current account balance, and changes in the interest rate have no effect on the balance of payments at all.

The relationship between the slopes of the BP and LM curves determines whether a policy shift moves the economy into balance of payments surplus or deficit. If the BP curve is flatter than the LM curve, an expansionary monetary policy that shifts the LM curve rightward will place the new IS LM intersection below the BP curve, creating a deficit. This understanding is essential for predicting the exchange rate and reserve implications of macroeconomic policy actions.

A currency depreciation improves export competitiveness and reduces import demand, strengthening the current account. This improvement means the economy can sustain a higher level of income at any given interest rate without the current account deteriorating to a point that requires capital inflows to offset it. As a result, the BP curve shifts to the right, reflecting a more favorable external position at every combination of income and the domestic interest rate.

The answer is True. To the right of the BP curve, income is higher than the equilibrium level for any given interest rate. Higher income raises imports and worsens the current account. At the prevailing interest rate, capital inflows are insufficient to offset this current account deterioration, leaving the overall balance of payments in deficit. This deficit puts downward pressure on the exchange rate under a flexible regime or drains reserves under a fixed regime.

The BP curve shifts leftward when the current account worsens independently of income and the interest rate. A fall in foreign income reduces export demand, and currency appreciation makes exports less competitive and imports cheaper. Both reduce net exports at every income and interest rate level, shifting the BP curve left. A rise in domestic interest rates does not shift the BP curve; it represents a movement along it. A rise in income also causes a movement along the BP curve, not a shift.

General equilibrium in the IS LM BP framework requires all three curves to intersect simultaneously at the same combination of national income and the interest rate. This single point ensures that the goods market, the money market, and the balance of payments are all in equilibrium at the same time. If any two curves intersect away from the BP curve, the balance of payments is not in equilibrium, creating pressures that lead to either exchange rate adjustment or reserve changes.

The answer is False. Domestic policy changes can indirectly shift the BP curve. For example, a fiscal expansion that raises income will worsen the current account, and if the exchange rate adjusts as a result, it can shift the BP curve. More directly, if the government uses exchange rate policy or if monetary expansion causes currency depreciation, the BP curve shifts rightward. While fiscal and monetary policies primarily shift the IS and LM curves, their effects on the exchange rate can also shift the BP curve.

When domestic interest rates rise, they exceed the level needed to attract just enough capital to offset the current account position at the prevailing income level. This excess capital inflow improves the overall balance of payments, placing the economy above the BP curve in surplus territory. Under a fixed exchange rate, the central bank must intervene to prevent appreciation, and under a flexible exchange rate, the currency appreciates, which shifts the IS and BP curves and restores equilibrium.

Points above the BP curve represent surplus because the interest rate is more than sufficient to attract capital inflows that offset any current account deficit. Points on the curve represent equilibrium. Points below represent deficit because income is too high or the interest rate too low to attract enough capital to offset the current account. The claim that points below represent surplus is incorrect; below the BP curve always means a balance of payments deficit.

A steep BP curve reflects low capital mobility. When capital flows respond weakly to interest rate differentials, a large increase in the interest rate is required to attract enough capital inflows to offset the worsening of the current account that comes with higher income. The BP curve becomes nearly vertical when capital mobility approaches zero, as only the current account determines external balance and interest rates have minimal influence on the capital flows needed to maintain balance of payments equilibrium.