Weekly Nugget: Analyzing financial situations using our online App

Analyzing the seemingly unstoppable growth of public debt

Using our Interest rates menu item

October 31st, 2025

Introduction

All of us care about what we may be able to purchase with the money we may be carrying in our pockets or with a certain amount of money if we are used to just using our credit cards.

The purchasing power of a given bill in a given currency changes over time. As an example, using AI we may ask ChatGPT or any other AI engine to get estimates of what one British pound (GBP) could purchase in the city of London overtime. We asked it to search in decade intervals, in the sixty-year span comprising the period 1920 till 1970 and to find the amount of current pounds equivalent to one pound in that year. The following table shows what it reported:

YearItemsToday's Equiv.
19203 kilograms of beef, or four dozen of eggs, or 10 liters of milk, one round train ticket London to Oxford. 55
193010 movie tickets, or 6 pints of beer at a Pub, or food for 2-3 days for a family of four. 75
19403 to 4 kilograms of bread, 1 kilogram of butter (if you could find it) or 4 gallons of gasoline (it was rationed). 60
1950Five gallons of gasoline, or six pints of beer, or 2 entrances to the theater, or 2 kilograms of beef. 40
1960Five liters of gasoline, 8 pints of beer, 10 movie theater entrances, twenty daily newspapers, 5 packs of cigarettes. 25
1970Three liters of gasoline, four pints of beer, two entrances to a movie theater, 3 or 4 large loaves of bread. 15
Table 1. Purchasing power of 1 pound and today's equivalent

The sources used by ChatGPT were the UK Office for National Statistics, National Archives and historical retail price reports.

We could have performed the preceding analysis using any currency and we would have obtained similar trends with varying great depression and World War II impacts.

Some currencies

Global Causes of Inflation

But why does purchasing power change, usually in the direction of less purchasing power? Well, you have to ask yourself Who issues money. What institution is in charge of making it available?

The answer is Central Banks acting on behalf of their governments. We even have a name that describes the rate by which every currency loses purchasing power: Inflation. It is a phenomenon that is present in all economies.

Inflation

It would seem that governments make more money available than the amounts that would keep purchasing power more stable, but why?

If we look at how much money governments spend every year, we may find a clue. But because we are dealing with different currencies, we have to ask the question appropriately. That is, we must ask how much each government spends with respect to a relevant local figure such as Gross Domestic Product, and then we must compare those figures over time.

Government Expenditure and Public Debt

The following table shows the government expenditure budgets as percentage of GDP, in nominal currencies in 1970 and 2024, for a few selected countries (all data was obtained from the International Monetary Fund )

Country19732023Change p.p.
United States 31.92%36.28%4.36
United Kingdom 43.51% 44.17% 0.66
Mexico 12.74% 28.67% 15.93
Japan 23.27% 41.16% 17.89
Brazil 11.0% 45.45% 34.45
Turkey 21.8% 33.18% 11.38
France 19.75% 56.99% 37.24
Table 2. Government Expenditure as percentage of GDP Source: IMF

The economies have grown, but government expenditures have grown much more. That is why they represent a larger portion of their GDPs. If governments obtain their income from taxpayers and their income has not grown as much as the government expenditure, clearly, they must either increase taxes or get the difference elsewhere, and here is where increasing public debt makes its appearance.

Country19732023Change p.p.
United States 42.59%118.73%76.14
United Kingdom 58.54% 100.03% 41.49
Mexico 19.96% 53.1% 33.14
Japan 15.9% 249.67% 233.77
Brazil 22.44% 84.68% 62.24
Turkey 23.05% 29.26% 6.21
France 15.83% 109.88% 94.05
Table 3. Government Debt as percentage of GDP Source: IMF

Why, is this important? From Finnugget's perspective interest rates are affected by each country's credit rating because within each economy, risk free interest rates in the local currency are the local government's issued bonds. The local Central Bank won't let government issued debt in local currency default so it may print more money and generate more inflation. In addition, all other bonds issued in that currency will presumably carry more risk and correspondingly will have to pay a higher interest rate. Therefore, financing projects locally will become more expensive.

Finnugget helps you determine what the real interest rate is for any effective or nominal interest rates and any inflation rate.

Increasing public debt

But more importantly, we should all ask ourselves where is this continuously increasing sovereign debt leading us? Are citizens in countries benefitting from additional services? Who benefits and why are governments continuously operating on deficits?

Conclusion

Ever increasing public debt has many consequences. Interest and principal must be paid and it will either result in less public expenditures, future tax increases or inflation. For now, we will leave you with these ideas to ponder on them. No matter where you look, you see the same pattern of increasing public debt. Why?

Let us know what you think. Until the next post!