How Overnight Repo Works: Mechanics and Example

An overnight repo is a one-day secured loan in which a borrower sells securities (usually Treasury bonds) to a lender and agrees to repurchase them the next day at a slightly higher price; the difference is the interest rate the borrower pays.

The Basic Transaction

Unlike an unsecured bank loan, a repo is always collateralized. The borrower gives up securities as safety; if the borrower defaults, the lender keeps the collateral and recovers losses. This collateral backing is why repo rates are typically much lower than unsecured rates—the lender’s risk is minimal.

A simple overnight repo involves five steps:

1. Borrower needs cash today. A bank, dealer, or hedge fund is short of funds but holds liquid securities (Treasuries, bonds).
2. Borrower sells securities to lender at face value. The lender delivers cash; the borrower delivers securities.
3. Overnight passes.
4. Borrower repurchases securities the next day at face value plus a small amount of interest (the repo rate).
5. Lender returns securities; borrower keeps the net interest paid.

The borrower’s cost is the difference between the repurchase price and the original sale price. The lender’s gain is the same difference.

A Worked Example

Suppose a securities dealer in New York holds $100 million face value of U.S. Treasury bonds. It needs $100 million in cash for one day to fund a position. It approaches a money-market fund with spare cash.

Day 1 (Transaction initiation):

• Dealer (borrower) sells $100 million in Treasury bonds to the money-market fund (lender)
• Dealer receives $100 million in cash
• Money-market fund receives Treasury bonds as collateral
• Agreed repo rate: 5.0% annualized

Day 2 (Repurchase):

• Dealer owes: $100 million × (1 + 0.05/360) = $100 million + $13,889
• Dealer repays $100,013,889 in cash
• Money-market fund returns the Treasury bonds to the dealer
• Money-market fund keeps the $13,889 in interest

The dealer has paid $13,889 for the one-day use of $100 million—an effective cost of 5% annualized. The money-market fund earned interest while staying fully collateralized by Treasury securities.

Who Uses Overnight Repo?

Banks, securities dealers, and money-market funds are the main players. A dealer might run short of cash at the end of the trading day and need to borrow overnight to square positions. A money-market fund with excess cash overnight can earn a better rate in repo than in overnight deposits. Large corporations and foreign exchange dealers also participate.

The Federal Reserve itself stands ready as a lender of last resort in the overnight repo market (the Fed’s Overnight Reverse Repo Facility). When repo rates spike—signaling panic or a cash shortage—the Fed offers to lend at a fixed rate, stabilizing the market. This happened dramatically in September 2019, when repo rates spiked to 10% and the Fed intervened heavily.

Collateral and Haircuts

The lender (money-market fund, bank) doesn’t just take the borrower’s word that the securities are worth $100 million. It may demand a haircut—a discount to the securities’ market value. If Treasury bonds are trading at par, the lender might only lend 99% of face value, keeping a 1% cushion against price moves.

For riskier collateral (corporate bonds, mortgage-backed securities), haircuts are larger. A repo using mortgage-backed securities might carry a 2–5% haircut, while a Treasury repo might have only a 0.5% haircut. The haircut protects the lender if the borrower defaults and the lender must sell the collateral in a downturn.

Overnight vs. Term Repo

Overnight repo matures the next day. Term repo runs for a week, a month, or longer. Overnight repo rates are more volatile because they reset daily; if credit conditions tighten, overnight repo rates can spike within hours. Term repo rates are smoother, reflecting longer-term expectations about funding costs.

The Repo Rate as a Market Signal

Overnight repo rates are highly sensitive to Fed policy and credit stress. When the Federal Reserve sets a higher federal funds rate, overnight repo rates typically track upward in tandem, because banks and dealers face a higher overall cost of funds. When credit stress flares—counterparties worry about each other’s solvency—borrowers may struggle to find lenders at any reasonable rate, and repo rates spike. Conversely, when monetary policy is loose and liquidity ample, repo rates fall.

Settlement and Risk

Modern repo typically settles on a same-day or next-day basis through central clearing houses like the Depository Trust & Clearing Corporation (DTCC). The buyer of securities and the seller of cash exchange simultaneously, reducing the risk that one side delivers but the other does not (settlement risk). For very large dealer-to-dealer repos, transactions may settle directly over-the-counter (OTC), but even then clearance is near-instantaneous.

Why Overnight Repo Matters

The overnight repo market is the plumbing of the financial system. It allows dealers to manage daily cash mismatches, enables money-market funds to earn competitive returns on short-term cash, and provides the Fed with a tool to implement monetary policy. When the repo market breaks (as in the 2019 crisis), credit conditions tighten sharply and borrowing costs spike across the economy.

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