An open economy is connected to the rest of the world through flows of goods, services, income, and capital, all recorded in the balance of payments. Reading the BOP correctly — and resisting the common errors about what a current-account deficit 'means' — is the foundation of international macroeconomics. This module builds that foundation.
The accounts
- The current account — trade in goods and services (exports minus imports), plus net primary income (interest, dividends, wages earned abroad), plus net secondary income (transfers, including remittances and aid). It records the country's net earnings from the rest of the world.
- The capital account — a small account for transfers of capital assets (debt forgiveness, migrants' transfers).
- The financial account — cross-border purchases and sales of assets: foreign direct investment (FDI), portfolio investment (stocks and bonds), other investment (loans, deposits), and the change in official reserves. It records how the current-account balance is financed.
The identity
The balance of payments balances
By construction (it is double-entry accounting), the balance of payments sums to zero: Current account + Capital account + Financial account = 0 The intuition: if a country runs a current-account deficit (it imports more than it exports, spending more than it earns abroad), it must be financing that deficit by a net inflow of capital (selling assets, borrowing, or running down reserves) — a financial-account surplus of equal size. A current-account deficit is, by identity, a capital inflow: the country is a net borrower from the world. A current-account surplus is a net capital outflow: the country is a net lender. The two sides are the same fact viewed from opposite ends, which is why you cannot change the current account without changing saving, investment, or capital flows.
The current account as saving minus investment
CA = S − I
A more illuminating identity: the current-account balance equals national saving minus domestic investment: CA = S − I A current-account deficit (CA < 0) means the country invests more than it saves — it imports the difference in the form of foreign capital. A surplus means it saves more than it invests at home and exports the surplus saving abroad. This reframes the current account away from 'trade' and toward saving and investment: a CA deficit is fundamentally an excess of domestic investment over domestic saving, financed by the rest of the world. This is why current-account balances are determined by the saving and investment decisions of households, firms, and governments — not just by trade competitiveness — and why blaming a CA deficit purely on 'cheap imports' or an overvalued currency misses the underlying saving-investment gap.
Is a current-account deficit bad?
The most common error is to treat a current-account deficit as inherently bad, like a household living beyond its means. It is not inherently anything — it depends on what is being financed and how. A deficit that finances productive investment (a country importing capital goods to build infrastructure and capacity, like a fast-growing developing economy) is healthy and expected — it is exactly how capital should flow from rich, capital-abundant countries to poor, capital-scarce, high-return ones, and the resulting assets will service the foreign borrowing. A deficit that finances consumption (an import binge, a fuel-subsidy splurge) with no corresponding productive investment is dangerous — it builds external liabilities with no means to repay them, the external counterpart of the good-debt/bad-debt distinction from the Sovereign Debt course. The questions are: what is the deficit financing (investment or consumption), how is it financed (stable FDI or flighty portfolio flows), and is it sustainable (will the external liabilities be serviceable)? A persistent deficit financed by short-term flows to fund consumption is a warning; a deficit financing high-return investment financed by FDI is fine.
The twin deficits
From CA = S − I and the fact that national saving includes government saving, a relationship emerges: a larger government budget deficit (lower public saving) tends, other things equal, to widen the current-account deficit — the 'twin deficits'. The intuition: when the government dis-saves (runs a fiscal deficit) and the private sector doesn't fully offset it, national saving falls relative to investment, so the gap is filled by foreign borrowing (a wider CA deficit). The relationship is not mechanical (private saving can offset, à la Ricardian equivalence; and investment varies), but it links the fiscal and external balances and is a recurring feature of crises — a country running large fiscal and current-account deficits simultaneously is doubly dependent on continued foreign financing, and doubly vulnerable when it stops (the sudden-stop and currency-crisis material to come). The twin deficits connect the public finance of the earlier courses to the external vulnerability of this one.
Exercise
Two developing countries each run a current-account deficit of 8% of GDP. Country A is importing machinery and inputs for an export-oriented manufacturing build-out, financed largely by foreign direct investment. Country B is importing consumer goods and fuel amid a large government budget deficit, financed by short-term portfolio inflows. (1) Use CA = S − I to describe what is happening in each. (2) Explain why the same 8% deficit is healthy for A and dangerous for B. (3) Apply the twin-deficits idea to Country B. (4) Explain what would make each country's deficit unsustainable.