Yield elasticity of bond value is the percentage

Percentage

In mathematics, a percentage is a way of expressing a number as a fraction of 100 . It is often denoted using the percent sign, “%”, or the abbreviation “pct”. For example, 45% is equal to 45/100, or 0.45.Percentages are used to express how large/small one quantity is, relative to another quantity...

 change in bond value divided by a one per percentage change in the yield to maturity

Yield to maturity

The Yield to maturity or redemption yield of a bond or other fixed-interest security, such as gilts, is the internal rate of return earned by an investor who buys the bond today at the market price, assuming that the bond will be held until maturity, and that all coupon and principal payments...

 of the bond. This is equivalent to saying the derivative of value with respect to yield times the (interest rate/value). This is equal to the MacAulay Bond Duration

Bond duration

In finance, the duration of a financial asset that consists of fixed cash flows, for example a bond, is the weighted average of the times until those fixed cash flows are received....

 times the discount rate

Discount rate

The discount rate can mean*an interest rate a central bank charges depository institutions that borrow reserves from it, for example for the use of the Federal Reserve's discount window....

, or the modified bond duration times the interest rate

Interest rate

An interest rate is the rate at which interest is paid by a borrower for the use of money that they borrow from a lender. For example, a small company borrows capital from a bank to buy new assets for their business, and in return the lender receives interest at a predetermined interest rate for...

.

If elasticity is below -1, or above 1 if the absolute number is used, it means that the product of the two measures, Value times yield or the interest income for the period will go down