What Is a Repurchase Agreement (Repo)?

A repurchase agreement, or repo, is a short-term loan in which one party sells a security — typically a government bond — to another party with an agreement to buy it back at a slightly higher price on a set future date. Economically it functions as a collateralized loan: the “seller” is really the borrower, the “buyer” is the lender, and the security is the collateral. The gap between the sale price and the repurchase price is the interest, expressed as the repo rate.

Repos are unglamorous by design — they’re plumbing, not a product most individual investors buy directly. But the repo market is one of the largest and most important corners of finance: it’s where banks, money market funds, hedge funds, and central banks manage short-term cash and collateral, often overnight, in transactions totaling trillions of dollars a day.

How a repo transaction works

Say a bond dealer needs cash overnight. It has a portfolio of Treasury bills it doesn’t want to sell outright. Instead, it enters a repo:

1. Today: The dealer sells $100 million of Treasuries to a cash-rich counterparty (often a money market fund) for, say, $99.99 million.
2. Tomorrow: The dealer buys the same securities back for $100 million.

The $10,000 difference is the interest on an overnight loan of roughly $100 million — annualized, that’s the repo rate. The lender never really wants to own Treasuries long-term; it wants safe, short-term, collateralized return on idle cash, which is exactly what a repo provides. From the lender’s side, the same transaction is called a “reverse repo.”

Because the collateral is high-quality and the term is typically overnight to a few weeks, repo is considered one of the safest forms of short-term lending — safer than an unsecured loan, since the lender can seize and sell the collateral if the borrower defaults.

Why repo exists

Dealers and banks hold large inventories of securities but need cash to fund day-to-day operations, settle trades, or meet margin calls. Selling securities outright to raise cash means giving up the position (and re-buying it later at an unknown price, with transaction costs each way). A repo lets them raise cash overnight without selling the underlying asset — they keep the economic exposure to the bond while borrowing against it.

On the other side, money market funds, corporate treasuries, and other cash-rich institutions need somewhere safe and liquid to park cash overnight, earning a bit of interest instead of letting it sit idle. Repo is often the default choice — safer than commercial paper, more liquid than a bank deposit, and backed by government securities as collateral.

Repo rates as a policy tool

Because repo is where huge volumes of short-term cash change hands daily, the repo rate is closely watched as a barometer of funding stress. When cash is scarce relative to available collateral, repo rates spike; when cash is abundant, rates fall.

Central banks — including the Federal Reserve — use repo operations directly as a monetary policy tool. In a repo operation, the central bank lends cash to primary dealers against collateral, temporarily adding liquidity to the financial system. In a reverse repo operation, it does the opposite: borrowing cash from money market funds and other counterparties against its own securities, temporarily draining liquidity. These operations are one of the main levers central banks use to keep short-term interest rates within their target range, complementing changes to the policy rate itself.

Repo vs other short-term instruments

	Repo	Money market fund	Treasury bill
Structure	Collateralized loan (sale + buyback)	Pooled investment in short-term instruments	Direct government debt
Typical term	Overnight to a few weeks	No fixed term (redeemable daily)	Weeks to one year
Collateral / backing	Securities pledged by the borrower	Diversified portfolio of short-term assets	Backed by the issuing government
Who uses it	Banks, dealers, funds, central banks	Retail and institutional investors	Governments, institutions, retail investors
Primary purpose	Short-term secured funding	Cash management with modest yield	Government financing / safe store of value

A money market fund is often the vehicle that actually participates in repo — many money market funds hold a substantial share of their assets in repo agreements, since it’s short-term, collateralized, and liquid, which fits the fund’s mandate well.

Repo and the yield curve

Repo rates sit at the very short end of the interest-rate spectrum, alongside instruments like Treasury bills. Persistent stress in the repo market — where rates spike well above the central bank’s target — can be an early warning sign of liquidity problems in the broader financial system, since it’s often the first place cash scarcity shows up. Watching the relationship between repo rates and the front end of the yield curve is one way analysts gauge whether short-term funding markets are functioning smoothly.

Repo also interacts with bond markets more broadly: a dealer’s ability to finance a bond position cheaply via repo affects how much it’s willing to pay for that bond in the first place, linking repo funding costs to prices across fixed income markets.

The takeaway

A repurchase agreement is a collateralized, short-term loan structured as a sale-and-buyback of securities — usually Treasuries, usually overnight. It lets dealers borrow cash without giving up their securities positions, and lets cash-rich institutions like money market funds earn safe, short-term yield. Because it moves such large volumes of cash daily, the repo market is also a key channel for central bank policy and a closely watched signal of stress or calm in short-term funding markets.