Methodology
This section provides an overview of the methodology used to gather, process, and visualize the data presented throughout Debtor Nation.
How We Got Here
Gross Federal Debt as a Share of GDP
Historical debt-to-GDP data are sourced directly from FRED's quarterly Federal Debt: Total Public Debt as Percent of Gross Domestic Product (GFDEGDQ188S). The pipeline converts FRED's percentage values to ratios for internal storage; the displayed percentages are unchanged.
This series measures gross federal debt, not debt held by the public. FRED
constructs it from Treasury's quarterly, end-of-period Federal Debt: Total Public Debt (GFDEBTN)—the sum of debt held by the public and intragovernmental holdings—and nominal Gross Domestic Product (GDP). FRED calculates ((GFDEBTN / 1,000) / GDP) × 100.
GDPDEF is not used in this calculation.
Federal Government Current Expenditures and Receipts
Federal expenditure and receipt data come from the Bureau of Economic Analysis's National Income and Product Accounts, Table 3.2, as published through FRED. Spending corresponds to Federal Government: Current Expenditures (FGEXPND), and revenue corresponds to Federal Government Current Receipts (FGRECPT). Both are quarterly series reported in billions of dollars at seasonally adjusted annual rates. These national-accounts measures are not the same as federal budget outlays and receipts. The app retains the annual rates as published rather than dividing them by four.
Inflation adjustment: Nominal
amounts are expressed in dollars of the latest common quarter using the BEA's GDP implicit price deflator (GDPDEF). The formula is nominal value × (latest-period GDPDEF / period GDPDEF).
Per-capita calculation: Nominal and inflation-adjusted amounts are divided by the quarterly BEA population series (B230RC0Q173SBEA), converted from thousands to people. The resulting figures are annualized per-person rates, not amounts incurred during a single quarter.
Share of GDP: Nominal expenditures and receipts are divided by quarterly nominal GDP. Because all three series are annualized rates, no further frequency adjustment is required.
Debt Accumulation
The interactive national-debt timeline uses the same quarterly Treasury total public debt series, GFDEBTN, normalized from millions to dollars.
Inflation adjustment: Debt is expressed in dollars of the latest common quarter using GDPDEF and the same formula described above.
Per-capita calculation: Nominal and inflation-adjusted debt are divided by the quarterly BEA population series.
Share of GDP: Gross federal debt is divided by quarterly nominal GDP after both series are converted to dollars.
Why the National Debt Matters
Shared Source and Projection Basis
All four projection charts are sourced from the Congressional Budget Office's The Long-Term Budget Outlook Data: 2026 to 2056, published February 25, 2026. The pipeline reads CBO's accompanying long-term budget projection workbook and joins the relevant tables by fiscal year.
The source workbook contains annual values for FY2011–FY2056. FY2011–FY2025 are historical values and FY2026–FY2056 are projections. The projections describe outcomes under CBO's current-law framework—that is, if current laws generally remained unchanged. All displayed source measures are percentages reported by CBO; the app does not apply a FRED series, inflation adjustment, or dollar conversion to these charts.
Federal Spending Projection
Spending by major category comes from CBO workbook Sheet 4, Outlays, by Category. The chart displays Social Security, major health care programs, other mandatory spending, discretionary spending, and net interest, each as a percentage of GDP. Its displayed range begins with the FY2025 actual value and continues with CBO's FY2026–FY2056 projections.
CBO's 2026 workbook reports Medicare, Medicaid, the Children's Health Insurance Program, and related marketplace subsidies together as major health care programs. The app retains that combined category rather than constructing separate program projections.
Federal Debt Held by the Public: GDP-Share Projection
Projected debt comes from CBO workbook Sheet 2, Debt and Deficits. The measure is federal debt held by the public as a percentage of GDP. It excludes intragovernmental holdings and therefore is not the same as the gross federal debt measure used in the How We Got Here section. CBO's reported percentages are displayed without changing their values. The chart begins with FY2025 as the actual benchmark and continues with projections for FY2026–FY2056.
Federal Spending Composition Projection
The composition chart uses the same categories and total spending measure from CBO
workbook Sheet 4. Unlike the spending projection chart, which shows each category as
a share of GDP, this view shows each category's share of total federal outlays. The
app calculates each displayed share as category outlays ÷ total outlays × 100. No
categories are reallocated or independently projected by the app. The chart begins
with FY2025 as the actual benchmark and continues with projections for
FY2026–FY2056.
Federal Deficit Projection
The annual total deficit comes from CBO workbook Sheet 2, Debt and Deficits, and is reported as a percentage of GDP. The chart displays the deficit's magnitude as a positive bar; it is equivalent to CBO's total outlays minus total revenues for each fiscal year. This is a federal budget deficit projection, unlike the NIPA current-expenditure and current-receipt gap described in the How We Got Here section. The chart begins with FY2025 as the actual benchmark and continues with projections for FY2026–FY2056.
Who Holds the Federal Debt
Who Holds U.S. Debt
The quarterly holder chart uses U.S. Treasury Fiscal Service data published through FRED. The directly sourced categories are Federal Debt Held by Federal Reserve Banks (FDHBFRBN), Federal Debt Held by Foreign and International Investors (FDHBFIN), Federal Debt Held by the Public (FYGFDPUN), and Federal Debt Held by Agencies and Trusts (FDHBATN). These are quarterly, end-of-period, not-seasonally-adjusted debt stocks.
Unit normalization: FDHBFRBN and FDHBFIN are reported in billions of dollars and are multiplied by one billion. FYGFDPUN and FDHBATN are reported in millions and are multiplied by one million. All four series are then joined on their common quarterly dates.
U.S. Public: This chart category
is derived as FYGFDPUN − FDHBFRBN − FDHBFIN. It therefore
represents domestic, non-Federal Reserve holders of debt held by the public rather
than a separately published FRED series.
Total and holder shares: The chart reconstructs total outstanding federal debt as debt held by the public plus agencies and trusts. Each holder's percentage is its nominal amount divided by that reconstructed total. Thus, the four bands sum to 100 percent apart from rounding.
Inflation adjustment: Each
nominal holder series is expressed in dollars of the latest common quarter using GDPDEF and the formula nominal value × (latest-period GDPDEF / period GDPDEF).
Foreign Holdings of U.S. Debt
The country map uses the U.S. Department of the Treasury's Treasury International Capital System Table 3, which reports foreign holdings of U.S. Treasury securities by country. The app uses the December 2025 monthly snapshot and displays total holdings, reported by Treasury in millions of nominal dollars.
Country mapping: Treasury country labels are matched to ISO country codes for the globe and ranking. Aggregate or unmatched rows that cannot be assigned to a mapped country are not displayed geographically.
Coverage: TIC totals include official and private foreign holders attributed to each country; they are not limited to foreign governments. Because the map measures Treasury securities on a monthly TIC basis while the holder chart uses a quarterly Treasury Bulletin series, the two foreign-holdings figures are related but are not expected to match exactly.
Where Does the Federal Government Spend Money?
Federal Government Outlays
Federal outlays by category come from the Office of Management and Budget's Historical Table 3.1, Outlays by Superfunction and Function, from the FY2027 President's Budget historical-tables workbook. The app reads the In millions of dollars section and displays annual fiscal-year actuals from FY1940 through FY2025. OMB's projected FY2026–FY2031 columns are not included in this chart.
Units and categories: Source amounts are multiplied by one million to convert them to dollars. The chart displays 18 function-level categories and groups them visually under National Defense, Human Resources, Physical Resources, Net Interest, and Other Functions. Parent superfunction totals are not plotted as additional categories, which avoids counting their component functions twice.
Share of total outlays: The main
chart calculates each function's displayed share as function outlays ÷ total federal outlays. Net
interest here is OMB's federal-budget measure and is distinct from the BEA
national-accounts interest-payment series described below.
Inflation adjustment: Dollar
comparisons are expressed in FY2025 dollars using OMB Historical Table 10.1's fiscal-year GDP chained price index. The formula is nominal outlays × (FY2025 GDP chained price index / fiscal-year GDP chained
price index). Percent-of-total values do not require an inflation adjustment because the
common deflator cancels from the numerator and denominator.
Comparison view and negative values: The draggable year markers feed the paired category charts and tables beneath the time series. OMB occasionally reports negative outlays for a function because of receipts or repayments. Those values remain in the source output but are rendered as zero in the positive stacked bars and omitted from the comparison rings. Undistributed offsetting receipts are also not a displayed category, so the visible positive categories should not be treated as an exact accounting reconciliation to 100 percent in every year.
Interest on Federal Debt
The quarterly interest chart uses the Bureau of Economic Analysis's National Income and Product Accounts Table 3.2 series published through FRED, Federal government current expenditures: Interest payments (A091RC1Q027SBEA). It is reported quarterly in billions of dollars at a seasonally adjusted annual rate. The app displays Q1 1947 through Q4 2025, converts billions to dollars, and retains the published annual rate rather than dividing it by four.
Accounting basis: This is a BEA national-accounts measure of federal interest payments. It is not the same series as OMB's fiscal-year net-interest outlays in the Federal Government Outlays chart.
Inflation adjustment: Nominal
interest payments are expressed in Q4 2025 dollars using GDPDEF and the formula nominal value × (Q4 2025 GDPDEF / period GDPDEF).
Share of GDP: The published annualized interest-payment rate is divided by quarterly annualized nominal GDP. Since both series are annualized, no additional frequency conversion is applied.
Per-capita calculation: Nominal and inflation-adjusted interest payments are divided by the BEA quarterly population series (B230RC0Q173SBEA), converted from thousands to people. These are annualized per-person rates.
Treasury’s Average Rate on Interest-Bearing Federal Debt
The monthly rate comes from the U.S. Treasury Fiscal Data Average Interest Rates on U.S. Treasury Securities dataset. The pipeline selects records whose security_desc equals Total Interest-bearing Debt and reads Treasury's avg_interest_rate_amt field. The displayed series runs
from January 2001 through December 2025.
Rate conversion: Treasury reports the rate in percentage points. The pipeline divides it by 100 for internal storage as a decimal ratio, and the chart formats that ratio back as a percentage without changing the underlying rate.
Measurement and coverage: Treasury calculates average interest rates from aggregate interest payments and total unmatured interest-bearing debt. The selected total covers marketable and nonmarketable Treasury debt, including Government Account Series. Treasury states that its aggregate rates for total marketable, total nonmarketable, and total interest-bearing debt exclude Treasury Inflation-Protected Securities and Treasury floating-rate notes.
Interpretation: This is a nominal average rate on the outstanding debt stock. It is not a current market yield, a rate on newly issued securities, or a rate calculated by dividing the app's interest payments by its debt series. Rates are not inflation-adjusted.
Retrieval: The pipeline requests the Treasury Fiscal Data API directly and uses an identically structured Treasury CSV export as a fallback if the API is unavailable.
Scaling the Federal Budget
The guided 3D budget tour uses FY2025 OMB Historical Table 3.1 outlay data, OMB Historical Table 1.1 receipts and deficit totals, and Treasury's total public debt outstanding from the Debt to the Penny dataset, dated May 7, 2026, for the accumulated-debt comparison.