Public debt is not paid off. It is rented.

Every bond is honored, but the outstanding stock is refinanced. The constraint therefore depends less on the stock alone than on its price and the volume to be rolled over each year.

A state pays off each of its securities, but almost never settles its total debt. Every maturing bond is paid to the cent, but the Treasury borrows to cover these repayments. Barring a budget surplus—and the French state budget has not seen one since 1974—the outstanding amount is refinanced rather than reduced. The principal constitutes a financing flow that leaves at maturity and returns through a new issuance. Interest represents the recurring budget burden. Amortizations determine the refinancing risk. While one measures the price of the debt, the others measure the confidence that the state must continually renew.

Yet, public debate is exclusively focused on the debt-to-GDP ratio—the refinanced stock expressed relative to a single year’s output. To be sure, this indicator is not absurd, since the stock forms the base of the rent. However, a base without a price or a repayment schedule does not tell you the bill. It is like assessing a borrower by their remaining principal relative to their income without asking for their interest rate or refinancing timeline.

The neglected indicator is the ratio of interest payments to revenue, read alongside the gross financing need and the monetary regime. This ratio measures the immediate constraint but is not sufficient on its own, because sustainability also depends on the primary balance—that is, the gap between interest rates and nominal growth, maturity, currency of issuance, and potential central bank support. This ratio does not replace debt-to-GDP: it reveals what the latter conceals.

When the stock no longer warns

Argentina defaulted in 2001 with a debt of about 60% of GDP because the market demanded nearly 35% on its 10-year dollar bond. The stock was not gigantic; it was its price and refinancing that had become impossible.

Japan offers the mirror image. With debt at more than twice its GDP, it should have sunk twenty years ago if the stock alone were enough to identify fragile countries. Yet it did not, notably thanks to near-zero rates, debt issued in its own currency, and the massive presence of its central bank. In 2022, interest absorbed only about 8% of public revenue. The 2026 budget projects 13 trillion yen for 83.7 trillion yen in tax revenue—more than 15%. For 2027, the Ministry of Finance is requesting 16.6 trillion yen, a 27% increase. In other words, nervousness emerges not when the stock crosses a symbolic threshold, but when its price feeds into the budget. Japan proves not that debt has no limit, but that the limit cannot be read in the stock alone.

In the United States, debt held by the public stands at around 101% of GDP, close to the 106% seen in 1946. The regimes differ, however, because the Federal Reserve capped long-term yields at 2.5% in 1942. As a result, post-war inflation and nominal growth rapidly eroded the real burden of the debt. Today, the average rate reaches 3.45%, compared to 1.54% in January 2021. In 2025, Washington paid $970 billion in net interest—more than the $917 billion spent on defense—representing 18.5% of federal revenue, a peak since 1991. The same relative stock as post-WWII, but an entirely unrelated financing regime.

The loop

Higher interest payments deepen the deficit. A larger deficit increases issuances. A growing stock produces more interest. If the market perceives higher risk, the required rate rises and accelerates the entire loop. When this rate persistently exceeds nominal growth while the primary deficit continues, debt can enter a self-reinforcing dynamic.

The Greece of 2011 devoted about one-sixth of its public revenue to interest without controlling the issuance of the currency in which it borrowed. Accounting scopes differ—federal revenue in the US, tax revenue in Japan, general government revenue in Greece—but the orders of magnitude clarify the constraint. Currency does not eliminate the rent: it alters its incidence across taxes, spending cuts, financial repression, and inflation.

France at the foot of the ramp

France borrows in euros, a currency whose issuance it does not sovereignly control. The ECB’s TPI could protect it against unjustified tensions, but it defends monetary transmission, not a state’s solvency. Its activation remains discretionary and conditional on debt deemed sustainable—and it has never been used!

The debt service of the French state reaches €63.6 billion in 2026, up from €51.8 billion in 2025, representing nearly one-sixth of its revenue. This figure is still at the bottom of the ramp. The average maturity is around eight and a half years, and low-coupon bonds are gradually being replaced under prevailing conditions.

Under a scenario combining weaker growth and a halved budget adjustment, the Cour des Comptes calculates general government interest payments at €107 billion in 2029. Simultaneously maintaining the energy transition, pensions, public services, and defense will force trade-offs that political debate continually postpones.

Three deadlines

If US interest payments continue to increase faster than revenue at the differential observed in 2026, they could exceed 20% of revenue as early as 2027.

If the Japanese budget adopts the ministry’s request and revenue remains close to 2026 levels, nearly one out of every five yen will be spent on interest in 2027.

Finally, the interest burden of all French public administrations will cross €100 billion before the end of the decade, barring a lasting drop in rates or a substantial reversal of deficits.

If these deadlines are met, the public debate will likely continue counting the stock, but it is the rent that will have changed in order of magnitude. Every security is repaid. The outstanding stock remains: economically, it is rented.

Three figures must therefore be visualized together: the rent relative to revenue, the volume to be refinanced, and the gap between the interest rate and nominal growth.

We count the debt. Yet the breaking point lies in its price and its timeline.