Debt Sustainability Analysis

Debt sustainability analysis (DSA) is a standardised method used by the IMF, World Bank, and credit analysts to project a country’s debt trajectory over five to ten years and assess whether borrowing will remain manageable. It simulates how debt grows or shrinks based on current primary balances (spending minus taxes, excluding interest), interest costs, economic growth, and exchange rates. If projections show debt stabilising at a comfortable level, the country’s finances are deemed sustainable; if debt spirals upward, sustainability is at risk, and policy changes are needed.

The core equation

At its heart, DSA is a straightforward accounting identity. The change in debt from one year to the next depends on three factors:

1. The primary deficit. If the government spends more than it collects in taxes (excluding interest), it must borrow. A large primary deficit swells debt.

2. Interest costs. The government must pay interest on existing debt. If the interest rate exceeds GDP growth, the debt ratio rises even if the primary balance is in surplus.

3. Growth and inflation. A faster-growing economy reduces the debt ratio mechanically (the denominator expands) even if absolute debt is stable. Inflation similarly helps, eroding the real value of debt.

The debt-dynamics equation, in simplified form, is:

Debt change = Primary deficit + Interest costs − (GDP growth + inflation)

If the primary deficit and interest costs exceed growth and inflation, debt rises. If growth and inflation exceed the deficit and interest, debt falls. Sustainability means the debt ratio eventually stabilises, neither exploding nor shrinking indefinitely.

DSA methodology

The IMF’s standard DSA follows a structured process.

Step 1: Historical baseline. Gather data on debt, interest rates, growth, and primary balances for the past five to ten years. This establishes trends and baseline assumptions.

Step 2: Baseline projection. Assume current policies continue unchanged. Project the primary balance (based on announced budgets and historical patterns), estimate interest rates (based on current spreads and maturity structure), and assume GDP growth rates consistent with consensus forecasts. Run the debt equation forward five to ten years.

Step 3: Stress tests. The baseline assumes benign conditions. Reality is uncertain. DSA performs alternative scenarios:

• Lower growth. What if growth disappoints by 1–2 percentage points? Higher unemployment and lower tax revenue worsen the primary balance.
• Higher interest rates. What if investor confidence falters and borrowing costs spike? Refinancing becomes expensive.
• Currency depreciation. For countries borrowing in foreign currency, a weaker exchange rate raises the real cost of debt service.
• Commodity shock. For commodity exporters, a price collapse reduces government revenue and growth.

Each scenario shows how the debt trajectory changes under adverse conditions.

Step 4: Assessment. Compare the baseline and stress-test projections to debt thresholds specific to the country. For advanced economies, debt above 90–100% of GDP is flagged as high; for emerging markets, thresholds are lower (60–75%) because they face higher borrowing costs and are more vulnerable to crises. If debt stabilises below the threshold under baseline and reasonable stress scenarios, the country is deemed sustainable. If debt rises above the threshold, especially under stress, sustainability is at risk.

An applied example

Imagine Country C has 70% debt-to-GDP, a 2% primary deficit, 4% interest costs, 3% nominal growth, and 40% of debt denominated in foreign currency. The baseline DSA projects:

Year 1: New debt = 2% (primary deficit) + 4% (interest) − 3% (growth) = 3 percentage points. Debt rises to 73%.

If growth holds at 3%, interest remains at 4%, and the primary deficit stays at 2%, debt will stabilise around 80% by year five and gradually decline thereafter. The projection shows sustainability.

Now stress the model. Assume growth falls to 1% and interest rates rise to 6%.

Year 1 stressed: New debt = 2% + 6% − 1% = 7 percentage points. Debt rises to 77%.

If these conditions persist, debt accelerates to 100%+ within five years. The threshold for Country C might be 90%; the stress scenario breaches it. This signals elevated risk. The government should consider tightening the primary balance (cutting spending or raising taxes) to reduce borrowing, or implementing reforms to boost long-term growth.

Limitations and judgement calls

DSA is a useful framework, but it is not a prediction engine. Several judgements undermine its precision.

Growth forecasts. Estimating potential growth over five to ten years is notoriously difficult. The IMF’s forecasts are often optimistic, especially for emerging markets, leading DSA to underestimate debt sustainability risks. Conversely, structural reforms can surprise to the upside.

Interest rates. Future borrowing costs depend on investor expectations, which shift rapidly. A DSA conducted in 2019 might assume 3% interest rates; by 2021, rates had fallen to 1%. Rates are endogenous—they depend partly on the debt trajectory itself, so the model can become circular.

Primary balance assumptions. Budgets are political; stated spending plans may not be credible. A country might promise austerity but lack political will to deliver. DSA assumes planned policies hold, which is often optimistic.

Structural breaks. DSA extrapolates from history. It cannot easily capture one-time events—a pandemic, a war, a natural disaster, a sudden loss of market access—that upend the trajectory.

For these reasons, DSA is best understood as a consistency check and a communication tool, not a precise forecast. It asks: given these assumptions, is the debt path stable? If not, what changes are needed? It flags risks; it does not eliminate judgment.

Use in surveillance and lending

The IMF publishes DSAs for countries under its surveillance programme and for those seeking loans. The analysis shapes lending conditions and policy recommendations. If a DSA shows unsustainable debt, the IMF typically requires the country to adopt a fiscal consolidation programme—reducing deficits, raising taxes, or cutting spending—before disbursing funds. This is contentious; austerity can deepen recessions and cause social hardship. Critics argue DSA is too pessimistic and pushes countries toward unnecessary tightening.

Creditors and rating agencies use DSA logic to price sovereign risk. A country with deteriorating DSA prospects faces higher borrowing costs, which validates the analysis but also becomes self-fulfilling: if investors lose confidence based on a bad DSA, they demand higher rates, worsening the actual trajectory.

Central banks also monitor DSA to assess the sustainability of government debt they hold, especially relevant in quantitative easing programmes where large public-sector purchases expand the balance sheet.

Recent applications

The COVID-19 pandemic illustrates DSA’s strengths and limitations. In 2020, most countries ran massive deficits to finance stimulus and healthcare. DSAs projected debt ratios rising sharply. Many analysts warned of unsustainability, especially for highly indebted countries. Yet economies rebounded faster than expected, growth strengthened, and inflation eroded real debt. Most countries’ DSAs in 2021–2022 showed improving debt paths—vindication for optimists, but a reminder that near-term growth surprises matter enormously.

Similarly, rising interest rates after 2022 tightened fiscal conditions globally. DSAs conducted in 2023 showed higher interest assumptions than those from 2021, materially worsening projections. The sensitivity of DSA to interest-rate assumptions underscores its vulnerability to macroeconomic shocks.

Strategic insights

DSA is most useful not as a forecast but as a discipline for policy dialogue. Countries with DSAs showing sustainability have policy space; they can afford near-term stimulus or social spending. Countries showing rising debt risks must act: tighten fiscal policy, accelerate reforms to boost growth, improve tax collection, or negotiate debt relief. The framework structures that conversation and makes implicit assumptions explicit.

For investors, a country’s DSA is a key input to credit decisions. A sovereign with a credible DSA showing manageable debt dynamics is less risky to lend to, all else equal. For multilateral lenders, DSA is a gate-keeping tool: no loans without a sustainable trajectory.

See also