Government debt

Public debt is discussed either as an imminent catastrophe or as an irrelevance. Both positions require ignoring something, and the something is usually the same: the composition of the debt and the currency it is denominated in.

Stock and flow

The deficit is the annual shortfall between spending and revenue. Debt is the accumulated total. A falling deficit still adds to debt; debt only falls when the government runs a surplus, or when the denominator grows.

The ratio and its denominator

Wealth Signal calculation

Debt-to-GDP can fall without repaying anything
Debt $100bn, GDP $200bn, ratio 50%. Next year debt rises 2% to $102bn while nominal GDP grows 5% to $210bn. The ratio falls to 48.6%. The debt grew, and the burden shrank. This is how several countries reduced very large post-war debt ratios — through sustained nominal growth rather than repayment.

Nominal growth includes inflation, which is why inflation erodes the real value of fixed-rate debt and why a government with large debts has an interest in it that is rarely stated out loud.

The distinction that matters most

Fact

Borrowing in your own currency is categorically different from borrowing in someone else's
A government issuing debt in a currency it controls cannot be forced into default by an inability to obtain the currency — the obligation is payable in something the state itself creates. A government borrowing in a foreign currency has no such option, which is why almost every sovereign default in modern history involved foreign-currency debt or a fixed exchange rate commitment.

This does not make debt costless. It relocates the constraint: the limit is not solvency but what happens to inflation and to the exchange rate if the debt is monetised. Those are real limits and they arrive through markets rather than through a missed payment.

What actually constrains a government

The interest burden. Interest as a share of tax revenue is a better measure than the debt ratio, because it is what actually crowds out other spending. It depends on rates, not just on debt.
r versus g. If the interest rate on debt is below the growth rate of the economy, the ratio falls without any fiscal effort. Above, it compounds upward. This single comparison determines whether debt is self-stabilising.
Maturity. Debt that must be refinanced soon is exposed to a rate spike. Long-dated debt issued at low rates locks in the terms for decades.
Who holds it. Domestic holders are generally more stable than foreign ones. Debt held by the central bank has different implications again — see quantitative easing.
Inflation. The genuine constraint on fiscal expansion: spending beyond the economy's capacity raises prices regardless of how it is financed.

The household analogy

Governments are routinely compared to families with credit cards. The comparison fails on three counts: a government does not retire, it can tax, and it issues the currency its debts are written in. It also fails in the other direction — a government cannot spend without limit, because real resources are finite and prices respond.

Why investors care

Sovereign debt trajectories affect the yield on government bonds, which anchors the price of every other asset. They constrain the fiscal response available in the next downturn. And in extreme cases they create pressure to inflate away obligations, which is a tax on everyone holding nominal claims — bondholders and cash savers first. See what a bond actually is.

Two numbers beat the headline debt ratio: interest as a share of revenue, and the gap between the average interest rate on the debt and nominal GDP growth.

Education, not advice. These lessons explain how things work. They do not tell you what to buy, and Wealth Signal does not publish recommendations. Full disclaimer.