12 July 2026 · Risk Free Rates Team
Why Does SOFR Sometimes Spike? Inside the Repo Market and the Fed's Backstop
SOFR is derived from the Treasury repo market, and repo rates occasionally jump at quarter-ends. Here's what causes the spikes, how the Fed's Standing Repo Facility contains them, and what it actually means for a SOFR loan's total interest.
Last updated 12 July 2026.
SOFR Is a Market Rate, Not a Policy Rate
Unlike the federal funds rate, which the FOMC sets directly, SOFR is derived each morning from actual transactions in the US Treasury repurchase (repo) market — where banks and dealers borrow and lend cash overnight using Treasury securities as collateral. Most days, SOFR tracks smoothly just below or around the effective fed funds rate. But a handful of times a year, especially around quarter-ends, the underlying repo rates it's built from jump — and anyone reading a daily SOFR compounding ledger notices the blip.
This post looks at why that happens, what the Federal Reserve has built to contain it, and — more practically — what it means for the total interest on a SOFR-based loan.
A Quick Recap: Where SOFR Comes From
As covered in our guide to SOFR, the New York Fed calculates the rate from three segments of the repo market: tri-party repo cleared through Bank of New York Mellon, bilateral Treasury repo cleared through the DTCC, and GCF Repo between dealers. Combined, these segments see well over $1 trillion in transactions on a typical day, which is what makes SOFR hard to manipulate compared to an estimate-based rate like LIBOR.
The methodology isn't frozen in time, either. In November 2024, the New York Fed made two changes to keep the calculation robust as more repo activity moved to central clearing: it began excluding transactions between affiliated institutions in the centrally-cleared segment (matching how tri-party repo was already treated), and it moved to trimming a consistent 20% of the lowest-rate transaction volume each day, rather than varying that trim daily. Both changes took effect with data from 22 November 2024 onward, and the Fed didn't revise any historical SOFR values.
Why Rates Spike at Quarter-Ends
The Federal Reserve's own research into quarter-end repo dynamics points to a fairly mundane cause: balance-sheet "window dressing." Around reporting dates, large dealers — particularly foreign banks — pull back from repo intermediation to shrink their reported balance sheets for regulatory and accounting purposes. Some shift activity into centrally cleared markets to net down exposures, while others simultaneously reduce how much cash they lend out (reverse repo) while increasing how much they borrow (repo). The combined effect is a temporary supply squeeze for cash that pushes rates up for a day or two.
The size of these spikes has grown over time. During 2017–2019, month-end jumps were typically a modest 5 to 10 basis points. By September and year-end 2024, the Fed's research found spreads between SOFR and the overnight reverse repo rate reaching as much as 25 basis points at quarter-ends. Further back, September 2019 is the standard example market participants point to: an unexpected cash shortage — before the Fed had today's tools in place — sent overnight repo rates sharply higher for several days and forced the Fed to intervene directly in the market.
The Fed's Backstop: The Standing Repo Facility
That 2019 episode is a big part of why the Standing Repo Facility (SRF) exists. Introduced in July 2021, the SRF lets primary dealers and other approved counterparties borrow cash overnight from the Fed at a fixed, pre-announced rate, pledging Treasuries, agency debt, or agency mortgage-backed securities as collateral. It acts as a ceiling on repo rates: if market rates spike above the SRF rate, eligible participants can simply borrow from the Fed instead, which caps how far a squeeze can push rates.
The facility has grown more central to how the Fed implements policy as bank reserves have declined from their post-pandemic highs. In June 2025, the New York Fed added a morning operation window (8:15–8:30 a.m. ET) alongside the existing afternoon session, specifically because dealers said earlier same-day access would better match their funding needs. Then, in December 2025, the FOMC went a step further and removed the $500 billion aggregate daily limit that had applied to SRF operations since their introduction — a sign of how much more the facility is now being used as a routine part of market functioning rather than an emergency-only tool. At the time, Fed Chair Jerome Powell described standing repo operations as "a critical tool to ensure that the federal funds rate remains within its target range, even on days of elevated pressures in money markets."
What This Actually Means for a SOFR Loan
For borrowers, the practical question is whether a repo spike meaningfully changes what they owe. In most structures, the answer is: not much, because of how SOFR is applied over a full interest period rather than on a single day.
| Loan structure | How a one-day repo spike shows up |
|---|---|
| Compounded SOFR in Arrears | One elevated daily rate compounds into the period average, but it's diluted across every other (normal) day in the period — see our guide to compounded SOFR in arrears |
| SOFR with lookback | The lookback period can shift exactly which day's spike lands in the period at all, and by how much weight it carries |
| Term SOFR | Already a forward-looking, market-priced rate for the full period, so it isn't affected by a spike that happens mid-period at all |
If you're using our RFR Loan Calculator with Compounded SOFR in Arrears, a quarter-end spike will show up as one unusually high row in the daily rate ledger — but because daily rates are weighted by the number of days they apply to and then compounded across the full period, a single elevated day rarely moves the total interest by much. It's a good reminder to look at the effective period rate, not any single day's printed rate, when evaluating what a loan actually costs.
Frequently Asked Questions
Does a repo spike significantly change my total loan interest? Usually not by much. In a compounded-in-arrears structure, one high day is averaged in with every other day in the interest period, so the effect on total interest is typically small unless the loan period is very short.
What is the Standing Repo Facility? It's a Federal Reserve facility, introduced in July 2021, that lets eligible dealers and institutions borrow cash overnight from the Fed at a fixed rate against Treasury or agency collateral — acting as a ceiling on repo rates during periods of cash scarcity.
Why did SOFR's calculation methodology change in 2024? The New York Fed adjusted the methodology in November 2024 to keep SOFR robust as more Treasury repo activity moved to central clearing, by excluding affiliated-institution transactions in the cleared segment and applying a consistent 20% trim to the lowest-rate volume each day.
Is repo market volatility a sign of broader financial stress? Not necessarily. Quarter-end spikes are largely a predictable, technical effect of dealer balance-sheet management rather than a signal of credit stress, which is part of why the Fed has built standing tools like the SRF to absorb them routinely.
Calculate Your SOFR Loan
Use our free RFR Loan Calculator to see exactly how daily SOFR rates — spikes included — compound into a loan's total interest, with a full daily rate ledger and Excel/PDF export. You can also browse our full blog for more on SOFR, SONIA, €STR, and how Fed policy affects borrowing costs.