We Are All Bond Traders Now

 | Feb 06, 2023 02:08PM ET

When I started working in the financial markets, bond traders were the cool kids. The equity guys drove Maseratis and acted like buffoons, but the bond guys drove sensible style like Mercedes and cared about things like deficits and credit. The authoritative word on this subject came from the book Liar’s Poker by Michael Lewis, about 1980s Salomon Brothers, where the trainees dreaded being assigned to do Equities in Dallas.

Back then, equities guys worried about earnings, the quality of management and the balance sheet, and the really boring ones worried about a margin of safety and investing at the right price. That seems Victorian now, but I guess so does the idea that sober institutions should only own bonds.

Down the list of concerns, but still on it, were interest rates. Ol’ Marty Zweig used to have a commercial in which he said “if you can spot meaningful changes (not just zig-zags) in interest rates and momentum, you’ll be mostly in stocks during major advances and out during major declines.” The reason that interest rates matter at all to a stock jockey is that the present value of any series of cash flows, such as dividends, depends on the interest rate used to discount those cash flows.

In general, if the discount curve (yield curve) is flat, then the present value (PV) of a series of cash flows (CF) is the sum of the present values of each cash flow:

…where r is the interest rate.

As a special case, if all of the cash flows are equal and go on forever, then we have a perpetuity where PV = CF/r. Note also that if all of the cash flows have the same real value and are only adjusted for inflation , and the denominator is a real interest rate, then you get the same answer to the perpetuity problem.[1]

I should say right now that the point of this article is not to go into the derivation of the Gordon Growth Model, or argue about how you should price something where the growth rate is above the discount rate, or how you treat negative rates in a way that doesn’t make one’s head explode. The point of this article is merely to demonstrate how the sensitivity of that present value to the numerator and the denominator changes when interest rates change.

The sensitivity to the numerator is easy. PV is linear with respect to CF. That is, if the cash flow increases $1 per period, then the present value of the whole series increases the same amount regardless of whether we are increasing from $2 to $3 or $200 to $201. In the table below, the left two columns represent the value of a $5 perpetuity versus a $6 perpetuity at various interest rates; the right two columns represent the value of a $101 perpetuity versus a $102 perpetuity. You can see that in each case, the value of the perpetuity increases the same amount going left to right in the green columns as it does going left to right in the blue columns. For example, if the interest rate is 5%, then an increase in $1 increases the total value by $20 whether it’s from $5 to $6 or $100 to $101.