Rolling Down Versus Curve Realisation in Interest Rate Markets

Summary

The document introduces two ways to describe how a bond’s yield changes as time passes. Under a static curve, a bond held for a year moves to a shorter maturity and takes the yield associated with that shorter point on the unchanged curve. Realisation instead compares the later yield with the forward yield implied earlier for that later date and maturity. The distinction is framed through an example involving expected central bank cuts: a realised rate reflects what actually happens, while a rolling comparison holds the earlier curve expectations fixed.

The discussion also notes that different curve regions may be interpreted differently. Short maturities can reflect time-dependent policy expectations, while longer maturities may be discussed in terms of persistent term premiums. Calculating roll in the front end may therefore require interpolation across time and maturities. The source is a question and partial explanation, not a worked numerical example or a formal calculation method; it does not specify an interpolation scheme or quantify the effects.

Key ideas

• Rolling compares a bond’s later yield with the shorter maturity point on an unchanged spot curve.
• Realisation compares the later yield with the forward yield previously implied for that date.
• Expected policy changes can make front-end rate movements reflect the passage of time and realised events.
• Longer-maturity curve segments may be interpreted through persistent term premiums.
• Calculating roll in the front end can require interpolation, but the document gives no specific procedure.

Tags

# Rates Curve 'Realising' vs 'Rolling'


# Rates Curve 'Realising' vs 'Rolling'












Just saw an exchange on X and would appreciate if anyone could try their hand at going into a bit more detail (and even maybe using an example) to breakdown the conceptual difference of rates curves 'rolling' vs 'realising' when it comes to interest rates curves

Also - if someone could explain what is meant by the "something clever to interpolate if you want to calc roll" that would be an amazing bonus.

Question - I am unclear on what is meant by the below:

"Bond rolling down = spot curve is unchanged. So your 5y bond which you’ve held for a year has the same yield as a 4y bond a year ago (when you bot the 5y). Curve realizing = the 5y bond you’ve held for a year now yields what the 1y forward 4y yield was a year ago.

An explanation was given, but i dont quite follow:

I think the natural way to think about it is that, if the Fed is predicted to cut in three weeks, then what is the overnight rate in four weeks. Realised = the lower rate. Rolled= the Fed didn’t cut but is also still predicted to cut in three weeks.

*Generally curves realise in the front end but roll in the long end. That is features like 10y30y are a generic and persistent term premium but the first 18 months are genuine time dependent predictions and you have to do something clever to interpolate if you want to calc roll. *

Edit: I realise if you're a seasoned practitioner you might be thinking that the above is already an explanation. What I mean is can you explain it to someone like they are a child.

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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.