Twin-Deficit Hypothesis

The twin-deficit hypothesis proposes that a larger government fiscal deficit tends to be associated with a larger current account deficit, which represents external imbalance. Fiscal expansion can reduce national saving and increase domestic expenditure, thereby increasing reliance on foreign saving, but the relationship is neither automatic nor necessarily one-for-one.

Accounting relationship

In an open economy, the identity CA = S - I states that the current account balance equals national saving minus domestic investment. Since national saving includes government saving, this can be written as CA = (Sp - I) + (T - G), where Sp is private saving and T - G is government saving.

• If private saving and investment remain unchanged, an increase in G - T, the fiscal deficit, reduces the current account balance and widens the current account deficit.
• The external deficit therefore reflects domestic investment exceeding the combined saving of households, firms and government.

Transmission from fiscal to external imbalance

Fiscal expansion may widen the external deficit through both saving and demand channels.

• A higher fiscal deficit lowers public saving, reducing aggregate national saving relative to investment.
• Higher government expenditure or lower taxes can raise aggregate demand, part of which falls on imports, worsening net exports.
• With capital mobility, higher interest rates may attract capital inflows and appreciate the currency, making exports less competitive and imports cheaper.

Why the deficits need not move together

The hypothesis is a ceteris paribus relationship, not an accounting rule requiring both deficits to change equally.

• Private saving may rise in response to fiscal expansion, partly offsetting the decline in government saving.
• Government borrowing may crowd out private investment, limiting the saving-investment gap.
• Exchange-rate movements, monetary policy, export demand and commodity prices can independently alter the current account.
• Causation may also run in reverse when an external slowdown weakens growth and tax revenue, thereby worsening the fiscal balance.