Read by function, not by agency, the second-largest increase in federal spending through July was interest

Federal spending is published two ways, and they classify the same dollars differently. One ledger sorts outlays by the department that spends them — interest lands inside Treasury, Medicare inside Health and Human Services. The other sorts them by function: what the money is for. We pulled the second one, Table 9 of the Treasury's Monthly Treasury Statement, for record_date 2026-07-31 (fiscal 2026 through July), with each function's prior-year figure printed beside it. Total net outlays through July were $6,284.2 billion, up $309.1 billion — 5.2% — from $5,975.2 billion in the same 10 months of fiscal 2025. Sorted by function, one line grew more than any other except Medicare: net interest rose $90.6 billion, to $931.4 billion from $840.8 billion, a 10.8% increase. That single function accounts for 29.3% of the government's entire $309.1 billion spending increase. Only Medicare grew more — up $131.1 billion (+15.9%). Together, Medicare and net interest added $221.7 billion, 71.7% of the net rise. Net interest grew more than the functions usually named as the drivers of federal spending. Social Security rose $70.7 billion, national defense $45.7 billion, the separate Health function $39.8 billion, and veterans' benefits $50.6 billion — each less than interest's $90.6 billion. The counter-current was Education, Training, Employment and Social Services, down $81.6 billion (to $82.0 billion from $163.7 billion), the largest decline of any function — a swing addressed in the caution below. By level, not just growth, net interest is now the third-largest function of government: Social Security $1,384.4 billion, Medicare $954.5 billion, net interest $931.4 billion, Health $845.2 billion, national defense $803.7 billion. Interest sits $23.1 billion below Medicare and $127.7 billion above defense. One precision the functional ledger forces: its net interest ($931.4 billion) is not the same figure as the department ledger's gross interest on the public debt, which runs higher. The function is net — gross interest less the interest the government collects, chiefly intragovernmental interest credited to trust funds. The two ledgers describe the same obligation at different points; this piece uses the net function throughout.

The following is analysis, not fact. The number itself — net interest up $90.6 billion — is arithmetic off two published columns. What the functional cut adds is where that number sits, and the answer is that it sits in a place the department ledger cannot show it. Read by department, interest is a subline inside a $1.4-trillion Treasury total, and Medicare is folded into Health and Human Services; neither stands alone. Read by function, both step out, and the two of them together carry nearly three-quarters of a year's spending growth. What separates net interest from the other four large risers is not its size — Medicare grew more — but that no one sets its level. Interest is paid under a permanent, indefinite appropriation that needs no annual vote; the big entitlements, Social Security and Medicare, are mandatory too, but their spending flows from benefit formulas Congress writes and can change, and defense is appropriated year by year. Net interest answers to neither a benefit formula nor an annual vote — it is the arithmetic product of the debt outstanding and the rates it carries, rising with the debt stock and the market whether or not anyone acts ^mmodeled. We do not, from this table, attribute the $90.6 billion to any single cause; a rise in net interest can come from a larger debt stock, higher rates on the parts that reprice, or a change in the interest the government receives, and Table 9 separates none of these. The delta is the fact; the mechanism is not one this ledger isolates. Read the two ledgers side by side and the same 10 months tell two stories. The department view, which a release-day desk is likelier to run, shows spending concentrated in a few big agencies. The functional view shows one of those concentrations is simply the cost of carrying the debt — a line that is now the third-largest thing the government does and, by dollars, its second-largest increase.

The sharpest caution is that this is the same $309.1 billion increase visible in the department ledger, re-sorted — not a second, independent finding. Whether net interest ranks second or third among growth drivers depends partly on the taxonomy: the functional ledger splits Medicare from the broader Health function. By level it is steadier — combining the two health functions ($1,799.7 billion) would leave net interest third, changing only what sits above it, not its rank. The robust claim is the delta itself — net interest up $90.6 billion, larger than any function's increase but Medicare's — not a ranking that shifts with how the categories are drawn. Second, the Education function's $81.6 billion decline should not be read as an $82 billion cut to schools. Net outlays for credit-heavy functions fold in credit-subsidy re-estimates under the Federal Credit Reform Act, which can swing a student-loan line by tens of billions in a year without a matching change in activity; the drop reads best as net accounting, not a halving of services ^mmodeled. Third, these are 10-month, year-to-date figures, not full-year results, and nominal dollars — a 5.2% nominal rise is smaller after inflation. Fiscal 2026 still has August and September to run, and the September close can reshuffle function totals.

From the topline, fiscal 2026 reads as ordinary growth: outlays up 5.2%, a wider deficit, the usual entitlement pressure. Sorted by what the money is for, the same 10 months put the cost of the debt itself among the government's three largest activities and its second-largest increase by dollars — a line that grew more than defense, more than Social Security, and second only to Medicare — one that answers to the debt outstanding and the rate market rather than to any benefit formula or budget vote. The figure that reads as routine and the function quietly climbing the table are the same statement, sorted two ways.