Repurchase Agreements: How Repos Work in Fixed Income Markets

Published: April 8, 2026

Article by Ryan O'Connell, CFA, FRM

Repurchase agreements — commonly called repos — are the lubricant of financial markets. They’re how dealers finance their Treasury inventory, how hedge funds leverage bond positions, and how the Federal Reserve implements monetary policy. Despite their critical role, repos remain one of the least understood money market instruments. This guide explains how repurchase agreements work, the mechanics of repo transactions, and how to calculate repo interest.

What Is a Repurchase Agreement?

A repurchase agreement (repo) is a short-term borrowing arrangement where one party sells securities to another with an agreement to repurchase them at a specified price on a future date. Although economically equivalent to a collateralized loan, repos are legally structured as a sale and repurchase — a distinction that matters for bankruptcy treatment.

The same transaction looks different depending on which side you’re on. If you’re lending cash and receiving securities, you’re doing a reverse repo. If you’re borrowing cash and pledging securities, you’re doing a repo. It’s the same trade — just viewed from opposite perspectives.

How a Repo Transaction Works

This legal structure as a sale — rather than a pledge — provides the lender with stronger rights in bankruptcy. If the borrower defaults, the lender owns the securities outright and can sell them immediately without going through bankruptcy proceedings. This “safe harbor” treatment makes repos attractive for short-term financing.

How Repurchase Agreements Work

Repos can be structured for different time periods and purposes. The most common distinction is between overnight and term repos.

Overnight repos mature the next business day. They’re the most liquid segment of the repo market and serve as the benchmark for short-term secured financing rates. The Secured Overnight Financing Rate (SOFR), which has replaced LIBOR as the primary U.S. dollar benchmark, is based on overnight repo transactions.

Term repos have maturities from two days to several months. They provide more stable financing but typically carry slightly higher rates than overnight repos. Borrowers use term repos when they want certainty about their financing costs.

Open repos have no fixed maturity date — either party can terminate with one day’s notice. They offer flexibility but expose borrowers to rollover risk.

Haircuts and Margin

The haircut (or initial margin) is the difference between the market value of the collateral and the cash lent. A 2% haircut means $100 of securities secures $98 of borrowing. Haircuts protect the lender against price declines in the collateral and vary by:

• Collateral type: Treasury securities typically have 1-2% haircuts; corporate bonds may require 5-10%
• Counterparty credit: Lower-rated borrowers face larger haircuts
• Term: Longer-dated repos may require higher haircuts
• Market conditions: Haircuts increase during periods of stress

Marking to market is typical in term repos. If the collateral’s value drops, the borrower may face a margin call requiring additional securities or cash. This protects the lender from credit exposure creeping up during the repo term.

General Collateral vs Special Collateral

Not all repo collateral is equal. The distinction between general collateral (GC) and special collateral drives significant rate differences in the market.

General collateral (GC) repos allow any eligible security from a defined basket — typically on-the-run Treasuries or agency securities — to serve as collateral. The lender cares about credit quality and liquidity, not the specific CUSIP. GC repo rates reflect pure financing costs and trade close to the federal funds rate.

Special collateral repos require a specific security. When a particular Treasury issue is in high demand — often because traders need it to cover short positions or deliver on futures contracts — it trades “special.” A security is special when its repo rate falls meaningfully below the GC rate.

Bilateral vs Tri-Party Repo

Repos settle through two primary mechanisms: bilateral and tri-party. The choice affects operational burden, counterparty exposure, and the types of participants involved.

In tri-party repo, the clearing bank handles collateral custody, daily valuation, margin calls, and substitution. This automation makes tri-party efficient for large-scale financing but less flexible than bilateral arrangements. The Federal Reserve conducts its repo operations through the tri-party system.

In bilateral repo, counterparties negotiate terms directly and manage collateral through their own custodians. Bilateral repos offer more flexibility on collateral eligibility and haircuts, making them popular for financing less liquid securities or when counterparties want customized terms.

Repo Fails and Market Stress

A repo fail occurs when the securities leg of a repo transaction doesn’t settle as scheduled. This happens when the seller cannot deliver the agreed securities — often because they were themselves failed to by another counterparty. Fails can cascade through the system, creating settlement gridlock.

To discourage fails, the Treasury Market Practices Group (TMPG) implemented a fails charge in 2009, updated in 2018. The daily charge equals the greater of (3% minus the TMPG reference rate) or 1%, whichever is higher, with a $500 monthly de minimis threshold. When short-term rates are low, this penalty creates a meaningful incentive to settle on time.

How to Calculate Repo Interest

Repo interest uses the money market convention of Actual/360 day count — the actual number of days divided by 360. This is standard for U.S. dollar money market instruments.

Risks and Limitations of Repurchase Agreements

While repos are generally considered low-risk instruments, they carry several risks that investors and borrowers must understand:

Counterparty risk: If the borrower defaults, the lender may face losses if the collateral has declined in value or is difficult to liquidate. The 2008 collapse of Lehman Brothers — a major repo borrower — highlighted this risk.

Rollover risk: Overnight and short-term repos must be continually refinanced. In stressed markets, lenders may refuse to roll repos, forcing borrowers to sell assets at distressed prices. This is a form of interest rate risk that affects leveraged investors most severely.

Fire sale risk: If many repo borrowers must liquidate collateral simultaneously, prices can spiral downward. This amplifies losses beyond what haircuts were designed to cover.

Rehypothecation risk: In some arrangements, lenders can re-use the collateral they receive, creating chains of exposure. If one link fails, the cascade can be unpredictable.

Common Mistakes

1. Confusing repo vs reverse repo: These are the same transaction from different perspectives. If you’re borrowing cash (pledging securities), it’s a repo. If you’re lending cash (receiving securities), it’s a reverse repo. The confusion often arises because both sides call their trade a “repo.”

2. Ignoring the haircut when calculating leverage: A 2% haircut means you’re financing 98% of the position value, not 100%. This affects your effective leverage and margin for error. The theoretical 50x leverage at a 2% haircut is a ceiling, not a target.

3. Underestimating rollover risk: Overnight repos must be refinanced every day. In a crisis, your counterparty may refuse to roll — precisely when you can least afford forced liquidation. Term repos reduce but don’t eliminate this risk.

4. Treating repo rates as interchangeable with risk-free rates: While repo rates are close to risk-free rates like fed funds, they can diverge significantly during stress. The September 2019 spike showed that repo rates can temporarily exceed even unsecured rates.

5. Forgetting the day count convention: Repo interest uses Actual/360, not Actual/365. Using the wrong convention will give you incorrect interest calculations — off by about 1.4% on an annualized basis.

Frequently Asked Questions