question regarding carry & roll of a bond

• I have a simple (and might be a dumb) question regarding the calculation of a bond's carry. If someone doesn't take into account cost of financing (e.g. the repo rate) then the bond's approximate return over a short time period is carry (coupon return + pull to par) plus roll-down return:

$$r\approx C\delta t +(y-C)\delta t -D\delta y$$

But on bloomberg and on several forums I frequently stumbled into the following expression for carry:

$$\text{carry} = \text{forward yield} - \text{spot yield}$$

Could somebody please clarify or derive what's the logic behind this?

Thanks

5 years ago

The formula you quote (forward minus spot) is the yield carry for a financed position.

The problem is that different people use the word carry to mean different things. The most commonly used convention, at least when we prepare analytical reports and quote sheets, is to use the word "Carry" to refer to the breakeven measure – it tells us how much yield can increase before a financed position starts to lose money. And of course, if spot yield rises to the forward yield, that's when it happens. (If you write out the math, you'll also see this is basically coupon income + pull-to-par - financing cost, in yield terms).

"Rolldown" is typically tabulated separately, and the sum of Carry and Rolldown (usually written as "RD&C") is the complete measure of how much I expect to make from a financed position, assuming an unchanged yield curve.

Thanks, could you please write out the math? It would a help a lot.

I think this definition of carry is a bit deceptive, because if you think of carry as how much you earn if the spot yield stays at the same level, then it is exactly the spot yield-repo rate for a financed position instead of the difference between the forward yield and the spot yield. But if you think of carry as a cushion against the change in spot yield before you start loosing money then it's correct.

"But if you think of carry as a cushion against the change in spot yield before you start loosing money then it's correct." And you also have to assume that the yield curve is flat, in order to separate the rolldown effect from the carry.

Carry is actually the most reliable part of bond returns; it's exactly known on an ex-ante basis and is not contingent on what happens to the yield curve. In dollar terms, carry = (ending accrued interest – starting accrued interest) – (starting price + starting AI) x repo rate x year fraction [or in words, carry = coupon income – financing cost]. Incidentally, forward price = spot price MINUS the quantity above; i.e., forward price = spot price – carry. This is how everything ties together.

For anyone coming across this answer the related answer here is a cross-reference to the same concept: https://quant.stackexchange.com/questions/36253/question-on-pure-carry-for-two-bonds/36261#36261 "LINK"

I was wondering if you could quickly elaborate on: "If you write out hte math, you will also see this is basically coupon income + pull-to-par - financing cost, in yield terms". How do you get this conclusion that the forward-spot is equal to this? Thanks in advance