How the Federal Interest Data Is Built

Three monthly series from the US Treasury, each as far back as its public API serves it. Net interest, national defense, total receipts and total outlays come from the Monthly Treasury Statement from March 2015, with fiscal year 2014 taken from the prior-year column of the September 2015 statement. Gross interest expense on the public debt by security type runs from May 2010. The average interest rate on the interest-bearing debt runs from January 2001.

The federal fiscal year runs from October 1 to September 30 and is named for the calendar year it ends in, so fiscal year 2026 is October 2025 through September 2026. A fiscal year is complete once its September statement is in; until then the pages show the months so far and say so.

Treasury provides the source observations; TFTC validates the rows before caching the parsed data.

Monthly Treasury Statement, Table 9

Receipts and outlays by budget function, from Treasury's Fiscal Data Monthly Treasury Statement dataset. The statement posts at 2:00 pm Eastern on about the eighth business day of the following month. Read in two date ranges, 2015 to 2020 and 2021 to date, so each response stays bounded. Only the complete, parsed snapshot is cached, for 24 hours; the raw responses are fetched without persistent caching.

Interest expense on the public debt outstanding

Treasury's Fiscal Data interest expense dataset: accrual-basis interest by security type, 38 lines a month, posted a few business days after month end. Read in two date ranges, 2010 to 2019 and 2020 to date.

Average interest rates on Treasury securities

Treasury's Fiscal Data average interest rates dataset, read for eight series (all interest-bearing debt, marketable and non-marketable debt, bills, notes, bonds, TIPS and floating rate notes), re-read every 24 hours.

Two different interest figures exist and the news uses both. Net interest is budget function 900 in the Monthly Treasury Statement: budget interest excluding interest credited to federal trust funds and other government accounts, and netting other budget interest receipts. It is the figure the budget, the Congressional Budget Office and the “interest now exceeds defense” headlines use. Gross interest expense counts every dollar of interest the debt accrues, including the part paid to federal trust funds on Government Account Series, and is reported separately from budget net interest.

Every comparison on these pages with defense spending, receipts or outlays uses net interest, because national defense, receipts and outlays are net budget figures from the same statement. Gross interest has its own page and is never set against defense or receipts.

Table 9 lines are picked by their line code, which has been the same in every statement the API serves, and each is confirmed against its label before use: net interest is line 320 (“Net Interest”), national defense is line 140 (“National Defense”), total receipts is line 120 and total outlays is line 340. The two totals are both labelled “Total”, so each is confirmed by the section row it hangs from (“Receipts” and “Net Outlays”) through the table's parent identifiers. If a line code ever stops matching its label, the line is found by the label and the section structure instead, and a month where that also fails is dropped and reported rather than published.

Interest expense lines are sorted into buckets by their category, group and type descriptions:

Treasury bills

The amortized discount on bills; bills pay no coupon.

Treasury notes

Accrued coupon interest plus amortized discount, less amortized premium.

Treasury bonds

Accrued coupon interest plus amortized discount, less amortized premium.

TIPS

Accrued coupon interest and the inflation compensation added to principal, plus amortized discount, less amortized premium.

Floating rate notes

Accrued interest plus amortized discount, less amortized premium. Issued since January 2014.

Savings bonds

Series EE, HH, I and other savings bonds.

Other public issues

Domestic and foreign series, State and Local Government Series, matured debt and miscellaneous interest.

Government Account Series

Interest paid to the government's own trust funds and accounts, such as Social Security and Medicare, on the securities they hold. This is the intragovernmental interest that net interest leaves out.

The total is always the sum of the buckets, and the public issues figure is the total less the Government Account Series. Average rate rows are matched by their security description; Treasury's July 2005 row spelled the marketable total without a space, and both spellings are read.

From the 6th to the 25th of each month the site checks each of the three feeds at 19:15 and 23:15 UTC for changes anywhere in each feed, using validated uncached reads and a fingerprint of its full history. Only changed feeds expire, along with the hub, dependent series pages and both JSON files. An MTS change also refreshes the email chart. A check that finds nothing new changes nothing. The Monthly Treasury Statement posts at 2:00 pm Eastern on about the eighth business day; the September statement, which closes the fiscal year, has posted as late as the 20th of October, which is why the window runs to the 25th. The pages use static rendering with a daily cache window as a backstop. A failed refresh retains the last valid cached snapshot. An initial request without valid data fails rather than publishing an empty dataset.

Each weekday morning an automated check compares the published data with the calendar and alerts TFTC when the previous month's statement is overdue on any feed: after the 16th of a month, or the 25th for the September statement.

Fiscal years use the statement totals, while comparisons over twelve months require twelve consecutive calendar months ending at the month shown.

Fiscal-year totals

Read from each statement's own fiscal-year-to-date column at the fiscal year's last statement, not summed by TFTC, so they match Treasury's published totals to the dollar. A year in progress uses the newest statement's year-to-date column; its change is against the statement's prior-year column, which covers the same months a year earlier.

Trailing twelve months

Exactly twelve consecutive calendar months ending at the month shown, summed by TFTC. Empty before twelve months are available or when any interior month is missing. Incomplete windows are excluded from records and the crossover.

Interest as a share of defense, receipts and outlays

Net interest divided by the same period's national defense, total receipts or total outlays, in percent. Fiscal-year shares use fiscal-year totals; monthly tables use trailing twelve months over trailing twelve months, because receipts arrive unevenly through the year.

Change on a year earlier

Net interest for a month against the same month a year earlier; for a fiscal year, against the prior fiscal year, or the same months of it when the year is in progress.

The crossover

The first month whose trailing twelve months of net interest exceeded the same twelve months of national defense, the first complete fiscal year where net interest exceeded defense, and, stated separately because single months swing with payment timing, the first single month above defense. The pages also say whether every trailing-twelve-month reading since the crossover has stayed above defense.

Gross interest by type

The sum of the Fiscal Data lines in each bucket for the month and fiscal year to date, as listed above. Shares are each bucket's part of the total.

Records

The highest single month, trailing twelve months and complete fiscal year of net interest, the highest trailing-twelve-month share of receipts, and the high and low of the average rate on all interest-bearing debt, each within the record on this page.

Every page and file states one update date, taken from the data: the newest month of the feed the page reads, stamped at 19:00 UTC on that month's record date (the last day of the month the statement covers), after Treasury's 2:00 pm Eastern release hour in both summer and winter time. The hub and the two JSON files carry all three feeds and take the newest. The same value is each page's structured-data dateModified, its sitemap lastmod and the dateModified in both JSON files, where updatedThrough gives the bare record date and sourcesUpdatedThrough gives each feed's. The stamp dates the data, not the day Treasury published it, which is about eight business days later.

The record has a defined starting date, and accounting choices affect comparisons with other published interest totals.

The record starts in 2015

The Fiscal Data API serves the Monthly Treasury Statement from March 2015 and the interest expense table from May 2010. Earlier budget-function history exists in Treasury and OMB publications but not in a public API this site reads, so it is not on these pages.

Monthly figures are lumpy

Interest payments fall on the 15th and at month end, TIPS inflation compensation accrues with the price index, and receipts arrive around tax deadlines, so a single month's net interest or share of receipts can look very different from the months around it. Compare fiscal years or trailing twelve months.

Months do not sum exactly to the year

Fiscal-year totals are read from the statement's year-to-date column, which carries small prior-period adjustments the monthly figures do not, so twelve months summed by TFTC can differ from the year's total by up to a few hundredths of a percent (fiscal year 2026: about $250,000 on $1.05 trillion of net interest, about $25 million on $965 billion of defense). The trailing-twelve-month figures are the sums; the fiscal-year figures are Treasury's.

Net interest is not only Treasury interest

Budget function 900 also carries smaller items, such as interest paid on tax refunds and interest received on loans, so it does not equal gross interest expense less trust-fund interest exactly.

The three feeds post on different days

The interest expense and average rate tables usually post before the Monthly Treasury Statement for the same month, so for a few days each month the gross and rate pages can be a month ahead of the net interest pages. Each page states its own data-through date.

Revisions

Treasury revises the Monthly Treasury Statement rarely; when it does, the next refresh re-reads the whole record and the revised figure replaces the old one without a note.

These comparisons use Treasury budget outlays. BEA national accounts interest uses a different accounting framework; CBO projections estimate future costs, and OMB historical tables may incorporate later revisions. Those measures should be identified separately when comparing a headline with this monthly record.

The CBO net interest primer explains why interest credited to government accounts and other interest receipts affect the budget measure. The gap between gross expense and budget net interest includes more than trust-fund interest.

Every figure is re-read from Fiscal Data on each refresh, so a correction Treasury makes shows up on the next run. Changes to sources, line selection or arithmetic are dated in the changelog below. If you find a figure that does not match the Monthly Treasury Statement, tell us through the contact page with the month and the line.

Treasury's figures are US government works in the public domain. TFTC's compilation and the derived totals, shares, crossover and records are free to reuse under CC BY 4.0. Credit:

Source: TFTC (tftc.io/federal-interest-expense), data through <month>.

The full record is at /federal-interest-expense/data.json, and the newest month, fiscal year, gross split and average rate are at /federal-interest-expense/latest.json. Both are open to any origin and carry the license, the attribution, the sources and the update fields described above.