Yield to worst

Yield to maturity (YTM) is the yield promised by the bondholder on the assumption that the bond will be held to maturity, that all coupon and principal payments will be made and coupon payments are reinvested at the bond's promised yield at the same rate as invested. It is a measurement of the return of the bond. This technique in theory allows investors to calculate the fair value of different financial instruments. The YTM is almost always given in terms of annual effective rate.
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The bond yield computed by using the lower of either the yield to maturity or the yield to call on every possible  call date.