Guide

Repo markets explained

Harbor Capital parked $420M of institutional cash in March while waiting for a private-credit allocation window. Treasury bills at auction cleared 5.28% but settlement was T+1 and the desk needed same-day availability for a margin call on a separate futures sleeve. Their treasury team split the pile: $280M into the Fed's overnight reverse repo facility (ON RRP) at 5.30%, $90M into a tri-party reverse repo with a primary dealer on U.S. Treasury collateral at 5.34% (GC repo), and $50M left in a government money market fund for next-day liquidity. Over 22 business days the blended sleeve earned 5.31% annualized with zero credit events and daily same-day redemption on the ON RRP leg. That allocation only makes sense if you understand what a repurchase agreement (repo) actually is — and why the largest money market in the world is built on selling bonds you intend to buy back tomorrow.

A repo is a secured short-term loan dressed as two bond trades: the borrower (“cash taker”) sells securities to the lender (“cash giver”) and agrees to repurchase them later at a higher price. The implied interest rate is the repo rate. Reverse repo is the same trade from the lender's side. Repos fund dealer inventories, hedge fund leverage, and corporate treasury cash — and they broke spectacularly in September 2019 and March 2020 when collateral and cash demands misaligned. This guide covers mechanics, haircuts, general collateral (GC) vs special repo, tri-party clearing, the Fed's ON RRP and Standing Repo Facility (SRF), the Harbor Capital cash refactor, a technique decision table against T-bills and fed funds, pitfalls, and a production checklist alongside duration and spread analytics.

Sale and repurchase: the basic trade

On day zero (trade date T):

Cash borrower (repo seller) — delivers collateral (usually U.S. Treasuries or agency MBS) to the counterparty and receives cash.
Cash lender (reverse-repo buyer) — pays cash and holds collateral.

On maturity (T+n, often overnight or one week):

The borrower repurchases the same securities at the repurchase price = cash lent + repo interest.
The lender returns collateral.

Example: lend $100M overnight at 5.20% on Treasury collateral. Interest for one day (ACT/360 convention) ≈ $100M × 0.052 / 360 ≈ $14,444. Repurchase price = $100,014,444. Economically this is a collateralized loan; legally many jurisdictions treat it as a true sale with a forward repurchase, which matters in bankruptcy (the lender may own the collateral outright if the borrower fails).

Key terms on the ticket:

Tenor — overnight, term (fixed maturity), or open (rolling daily until terminated).
Collateral type — U.S. Treasuries, agencies, MBS, or corporate bonds (credit repo, less common for cash investors).
Haircut — the lender lends less than the collateral's market value (see below).
Tri-party vs bilateral — a clearing bank (e.g. BNY Mellon) holds collateral and marks positions daily in tri-party; bilateral is direct between two institutions.

Haircuts: why you lend $97 on $100 of bonds

The haircut is the discount applied to collateral market value when determining how much cash the borrower receives:

cash lent = collateral market value × (1 − haircut)

A 3% haircut on $100M face (at par) Treasuries means the borrower receives $97M cash. If the bond price drops before repurchase, the lender may issue a margin call for additional collateral or cash. Haircuts rise with:

Collateral risk — Treasuries 0–2%, agencies 2–5%, corporates 5–15%+.
Tenor — longer term = more price uncertainty.
Market stress — haircuts widened sharply in March 2020 as dealers demanded more cushion on the same bonds.

For cash investors, haircuts are protection: if the borrower defaults, the lender can sell collateral. The haircut should exceed expected price decline plus liquidation costs. Under-collateralization was a central failure mode in 2008 for mortgage-repo funded structures.

GC repo vs special repo

Not all repo trades on the same rate. Two regimes matter:

General collateral (GC) repo — the borrower posts “any eligible Treasury” from a basket; the lender cares about credit quality of the class, not a specific CUSIP. GC rates cluster near the risk-free short end and track fed funds / SOFR closely. Harbor's $90M tri-party leg was GC repo.
Special repo — a specific security is in high demand (often newest on-the-run Treasuries used to cover short sales). Borrowers of that bond pay a specialness spread: the repo rate drops below GC (sometimes near zero or negative) because lenders want that exact CUSIP as collateral. The lender earns a lower repo rate but can often lend the bond out in the securities lending market, capturing the specialness premium elsewhere.

For treasury desks parking cash, GC reverse repo is the default. Chasing special repo as a cash investor rarely pays unless you have securities lending infrastructure. Dealers live in both markets simultaneously — borrowing special to deliver shorts, lending GC to fund inventory.

Tri-party repo and the dealer ecosystem

Roughly two-thirds of U.S. repo volume is tri-party: cash lenders (money funds, corporations, central banks) face a clearing bank, not each dealer individually. The clearing bank:

Values collateral daily and applies haircuts.
Substitutes collateral within eligible baskets (if one bond matures, swap in another).
Settles cash and securities legs.

Primary dealers borrow in tri-party to finance Treasury and MBS inventories between auctions and client trades. When dealer balance sheets are constrained (quarter-end leverage ratios, risk-weighted asset limits), repo rates spike — the September 2019 repo squeeze saw overnight GC rates jump above 10% intraday while the fed funds target was 2.00–2.25%. The Fed responded with overnight and term repo operations, then built permanent backstops (below).

Bilateral repo (often between two dealers or a hedge fund and a dealer) allows bespoke collateral and terms but demands credit lines, legal agreements (GMRA), and operational margin workflows. Most institutional cash pools avoid bilateral unless they have a dedicated repo desk.

Fed facilities: ON RRP and the Standing Repo Facility

After 2008 the Federal Reserve became a structural participant in repo markets:

Overnight Reverse Repo (ON RRP) — approved counterparties (money funds, GSEs, banks) lend cash to the Fed overnight, collateralized by Fed securities. It sets a floor on short rates: private lenders must beat ON RRP to attract cash. Harbor's $280M leg used this facility for government-only collateral and same-day liquidity. Rate is set by the FOMC alongside the interest on reserve balances (IORB) corridor.
Standing Repo Facility (SRF) — introduced after 2019–20 stress. Primary dealers (and later others) can borrow from the Fed overnight against Treasury/agency/MBS collateral at a ceiling rate. It caps how high GC repo can spike in a squeeze.
Term repo operations — periodic Fed lending for weeks at fixed rates during stress; distinct from the standing facility's daily window.

Together, ON RRP and SRF bracket overnight funding costs. When ON RRP usage is high (trillions at peak 2022–23), it signals cash is abundant and private repo is uncompetitive. When ON RRP drains toward zero, cash is re-entering the banking system and private repo rates matter more for marginal funding.

Harbor Capital cash sleeve refactor

Harbor's starting point was a single government MMF position earning 5.18% seven-day yield with T+1 settlement on large redemptions. Constraints for the March window:

Same-day access to at least $200M for futures margin.
No credit exposure beyond U.S. government collateral.
Minimize drag from negative spread to T-bill auction levels.

Refactor steps:

Opened ON RRP access via existing custodian (Fed master account linkage).
Negotiated tri-party reverse repo line with two primary dealers; compared all-in rates net of custody fees.
Kept $50M in MMF as operational buffer for unexpected T+0 wires the repo lines could not cover.
Daily dashboard: ON RRP rate vs dealer GC reverse vs MMF yield vs next T-bill auction stop.

Outcome: +13 bps annualized vs MMF-only, with $280M redeemable same day through ON RRP. Operational cost: two additional settlement reconciliations and a 15-minute dealer cutoff vs 6:30 p.m. ET for ON RRP. Controllers tagged ON RRP as Fed balance sheet exposure (not bank deposit insurance) for disclosure footnotes.

Technique decision table

Need	Prefer	Why not the alternatives
Park government cash overnight, same-day exit	ON RRP or GC tri-party reverse repo	T-bills require auction/T+1; MMF may gate large redemptions
Fund bond inventory as a dealer	Tri-party or bilateral repo (borrow cash)	Unsecured fed funds lacks collateral; more credit line usage
Retail cash, no repo desk	Government MMF or T-bill ladder	Repo requires Fed or dealer onboarding and legal docs
Weeks-term financing on specific bonds	Term repo or securities lending	Overnight rolls expose you to rate spikes at month-end
Short specific Treasury (hedge)	Special repo borrow + securities lending	GC repo may not deliver the on-the-run CUSIP you need

Pitfalls

Treating repo as risk-free — Lehman and MF Global showed collateral ownership and rehypothecation chains can strand lenders. Stick to U.S. government collateral for cash parking.
Ignoring haircut changes — stress widens haircuts; borrowers face sudden cash calls. Lenders may receive collateral they cannot liquidate at modeled prices.
Quarter-end window dressing — dealers shrink balance sheets; repo rates become erratic last days of quarter. Do not assume March 31 overnight equals mid-month average.
Confusing repo rate with bond yield — repo is financing cost on collateral, not compensation for credit spread or duration risk on the underlying bond.
Operational cutoffs — ON RRP submission deadlines and dealer triparty cutoffs differ; missing cutoff leaves cash idle overnight.
Rehypothecation opacity — in bilateral repo, ask whether your collateral can be re-lent. Tri-party limits this but read the agreement.

Production checklist

Confirm counterparty eligibility: ON RRP via Fed, tri-party via dealer onboarding.
Restrict collateral schedule to Treasuries/agencies for cash investment mandates.
Document haircut schedules and margin call timelines in the investment policy.
Compare all-in yield: repo rate minus custody, admin, and wire fees.
Model same-day vs T+1 liquidity for each leg; keep MMF buffer if needed.
Reconcile daily: cash balance, repo maturity schedule, collateral marks.
Monitor GC vs special spreads for signs of collateral scarcity (systemic stress).
Track Fed ON RRP take-up and SRF usage as macro liquidity indicators.
Stress-test quarter-end and year-end repo rate spikes on rolled positions.
Align accounting: repo collateral may be off-balance-sheet for borrower but disclosed in footnotes for lenders.

Key takeaways

Repo is a collateralized overnight loan structured as a bond sale plus forward repurchase — the repo rate is the financing cost.
Haircuts protect lenders; margin calls protect them further when collateral prices fall.
GC repo is the generic rate for cash parking; special repo reflects scarcity of specific securities.
Fed ON RRP floors and SRF ceilings bracket short-term rates — Harbor blended ON RRP, tri-party reverse, and MMF for liquidity tiers.
Repo plumbing breaks in stress (2019, 2020) — treasury desks need cutoffs, collateral schedules, and quarter-end playbooks, not just the headline rate.