When we think about debt in an
economy, the central question isn’t just how much debt we have, but rather how
productive that debt actually is. To answer this, we looked at the Marginal
Productivity of Debt (MPD).
What is MPD?
Marginal Productivity of Debt
measures how many dollars of incremental economic growth (i.e., Gross Domestic
Product, or GDP) are generated for every new dollar of net credit added to the
economy over a given period. Mathematically, MPD is represented as follows:
Change in Nominal GDP ÷ Change
in Net Debt
What this measure tells us:
If, for example, MPD is +$0.75, it means that for every $1.00 of new borrowing,
our annual economic output increased by $0.75. If, let’s say, MPD drops to
+$0.35, the economy requires almost $3.00 of new borrowing just to generate
that same $1.00 of growth (simply divide 1 over 0.35 to observe the precise
value). As we can see, MPD is a direct temperature check, if you will, on the
“bang for the buck” of credit expansion.
Data and Methodology
To build a clear, historical
picture from 1952 through 2026, we pulled macroeconomic data directly from our
favorite tool, the Federal Reserve Economic Data (FRED) database from the St.
Louis Fed:
1. Economic Output Data
Series (Numerator): “GDP” (Gross Domestic Product, Quarterly, Billions of
Dollars)
2. Total Nonfinancial Debt
Data Series (Denominator): “TCMDODNS” (Domestic Nonfinancial Sectors; Debt
Securities and Loans; Liability, Level, Millions of U.S. Dollars). This
captures borrowing by households, nonfinancial businesses, and federal/state
governments, while stripping out financial sector intra-bank transactions to
avoid double-counting.
3. Data Transformations
Applied:
- Evaluated the 1-year trailing
change (“change from Year Ago”) for both GDP and Debt to capture the rolling
12-month net expansion.
- Harmonized units by scaling
debt from millions into billions using the formula: (∆GDP
x 1000) ÷ ∆TCMDODNS
Key Observations from 70+ Years of Data (1952-2026)
Let’s examine what the graph
we generated shows (red circle and lines on the graph are my markings):
The 70-year shift in U.S. debt
efficiency is stark, and the core takeaways from this analysis are as follows:
1950s – 1970s: High Efficiency Era (range from ~+$0.60 to ~+$0.85
per $1.00 of debt):
- Debt directly funded
industrial capex, factory equipment, and physical infrastructure.
1980s – 2026: Financialization & Diminishing Returns Era (range
from ~+$0.25 to ~+$0.40 per $1.00 of debt):
- Shift toward asset
refinancing, real estate turnover, and servicing legacy debt overhang.
1. The Structural Decline in Debt Efficiency is Real
Prior to the early 1980s, the
U.S. economy routinely generated ~+$0.60 to ~+$0.85 in annual GDP for every
$1.00 of net new debt issued outside of recessions. Starting in the early
1980s, this baseline experienced a persistent structural downward shift. For
the past two decades (2000s through 2026), the baseline has hovered between ~+$0.25
to ~+$0.40. It now takes significantly more credit to generate the same unit of
economic expansion.
2. Diminishing Marginal Returns to Credit
Why did this happen? Here we
draw from our experience and understanding to come up with the likely culprits.
From Productive Capex to Asset Refinancing: In the post-war era,
debt primarily funded tangible, capacity-expanding capital investments (e.g.,
manufacturing plants, highways, utility grids). Over the last four decades, an
increasing share of borrowing shifted into real estate asset turnover,
corporate financial engineering (e.g., share buybacks and M&A), and
government deficit spending.
The Drag of Debt Overhang: As total accumulated debt expanded
relative to GDP, a growing share of every newly borrowed dollar had to be spent
simply servicing, rolling over, and refinancing existing debt rather than
building new productive capacity.
3. Debt Does Not Prevent Recessions (Credit Cycle Vulnerabilities)
I like to think of this part
as a double-edge sword, because debt is a powerful tool to amplify returns both
on the way up and on the way down. You will see in a moment what I mean.
Indeed, while credit is a powerful tool at pulling future demand into the
present during expansionary periods, it does not immunize the economy from downturns:
- In every major recession –
1954, 1958, 1974, 1982, 1990, 2001, 2008, and 2020 – the MPD dropped sharply,
dipping deep into negative territory (reaching ~-$0.40 during the Great
Financial Crisis).
- Because debt creates fixed
payment obligations while economic income fluctuates, high leverage actually
amplifies downturns. When income contracts, borrowers are forced to slash
spending, payroll, and investment to service their debt, turning mild slowdowns
into sharper contractions. On this point, I think the so-called Austrian School
of Economics has it mostly right in their view of the economic cycle, but that
is a story for another day.
Conclusion:
Debt is a critical tool for
economic growth, but it has its limits. The historical data from 1952 to 2026
shows that the U.S. economy is getting diminishing marginal output from each
new dollar of credit, and accumulating more debt cannot eliminate the cyclical
reality of recessions. Unless something structural occurs in the economy that
improves the marginal output from each new dollar of credit, the U.S. will at
some point find itself facing serious economic issues. We cannot indefinitely
borrow ourselves to prosperity.