On-the-Run vs Off-the-Run Treasury Spread

The on-the-run/off-the-run Treasury spread is the yield difference between the most recently issued (on-the-run) Treasury of a given maturity and an older Treasury of the same maturity that is no longer the primary benchmark. The spread exists because on-the-run Treasuries are more liquid — easier to buy and sell in size — and investors will accept a lower yield in exchange for that convenience and lower trading costs.

Why freshly issued bonds trade at a premium

When the U.S. Treasury issues new 10-year bonds, those bonds become the “on-the-run” or “current” issue. Dealers and institutional investors naturally concentrate their trading and inventory in this newest instrument because:

1. Liquidity concentration: Traders know where the action is. Bid-ask spreads are tighter for on-the-run Treasuries, and large orders can be executed quickly.
2. Lower transaction costs: With tighter spreads and deeper order books, the round-trip cost of buying and selling on-the-run bonds is lower.
3. Benchmark status: The on-the-run is the reference point for pricing other fixed-income instruments and for derivatives.
4. Collateral value: In repurchase agreements (repos), on-the-run Treasuries often command special rates because they are easier to rehypothecate and trade.

Because on-the-run Treasuries are more desirable, investors will accept a lower yield — they pay a premium price — to hold them. An off-the-run 10-year Treasury from six months ago must offer a higher yield to compensate for its inferior liquidity. The difference is the on-the-run/off-the-run spread.

Typical magnitude and variation

The spread typically ranges from 2 to 10 basis points for heavily traded maturities like the 10-year, though it can widen dramatically in stressed markets. During liquidity crises, such as March 2020, the spread blew out to 30+ basis points as investors shunned anything less liquid than the most on-the-run instruments.

The spread is not constant across the yield curve. It tends to be largest at the most actively traded maturities (2-year, 5-year, 10-year, 30-year) and smaller for less liquid parts of the curve. It can also vary intraday, widening as market stress rises and narrowing when risk appetite returns.

Implications for yield curve measurement

Yield curve construction requires careful treatment of the on-the-run/off-the-run distinction. If a curve is built using only on-the-run Treasuries, the curve reflects liquidity-adjusted yields, not pure interest rate expectations. The yield curve will appear artificially steep or flat depending on which on-the-run bonds happen to be trading at wider or narrower spreads.

Many central banks and research institutions construct “smoothed” or “fitted” yield curves by including both on-the-run and off-the-run bonds, then adjusting for the liquidity premium. This approach isolates the term structure of interest rates from short-term liquidity noise.

The lifecycle of an on-the-run bond

When a new Treasury is first issued, it becomes the on-the-run (or “when-issued”) instrument. It commands the tightest bid-ask spread and the largest dealer inventory. Days later, the Treasury issues a new bond at a different maturity (e.g., a new 5-year when yesterday’s 5-year was already issued), and the previous on-the-run becomes “old” or “off-the-run.”

As bonds age, trading volume declines. Some investors prefer to hold Treasuries to maturity and are indifferent to liquidity, so a small secondary market persists. But the bulk of trading activity dries up. An off-the-run Treasury from years earlier may trade only infrequently and in modest sizes.

Eventually, an off-the-run bond can become so illiquid that the on-the-run/off-the-run spread reflects not just liquidity but default risk concerns (which are negligible for Treasuries) or technical supply imbalances. Treasury dealers sometimes hold large inventories of old bonds and must offer steeper discounts to clear them.

The role of dealers and repo markets

Treasury dealers have a vested interest in maintaining the on-the-run/off-the-run spread. By holding inventories of older, off-the-run bonds, dealers can profit from the liquidity premium when spreads widen and narrow. They also benefit from repo financing, where on-the-run bonds often trade at “special” rates — lower repo rates that reflect their higher collateral value.

During periods of stress, dealers reduce inventory and widen spreads to compensate for risk. This amplifies the on-the-run/off-the-run phenomenon. During normal times, dealers’ competition narrows spreads, making it cheaper for investors to access the most liquid instruments.

Market efficiency and arbitrage

The on-the-run/off-the-run spread is not an arbitrage opportunity in the textbook sense because it compensates for real economic differences: the cost of immediacy and the value of liquidity. An investor cannot eliminate the spread by buying off-the-run and shorting on-the-run; the off-the-run position is harder to borrow and will eventually be called away.

However, the spread does represent a departure from simple yield curve theory, where all bonds of the same maturity should have the same yield. In practice, market microstructure — order flow, inventory, and liquidity — matters.

Practical relevance for investors

For a long-term buy-and-hold investor, the on-the-run/off-the-run spread is a trading cost hidden in plain sight. Buying an off-the-run Treasury with a 5 basis point higher yield is rational if the investor can hold it to maturity. But for traders seeking to unwind a position or rebalance dynamically, the spread works against them.

Portfolio managers often exploit the spread opportunistically. If spreads are unusually wide, they may rotate from on-the-run to off-the-run bonds, pocketing the yield pickup. If spreads compress (e.g., after a new auction when the on-the-run bond is issued), managers may shift back.

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