Duration is a reasonably good estimate of bond price movements upon small interest rate moves. However, it assumes that bond price moves linearly with interest rates, which is not true especially for larger rate moves. Convexity corrects duration for this non-linearity as follows:
= ½ x Convexity x (Rate Move in decimals ^ 2) * 100
In Example 1, if the convexity is 8, the correction to duration would be:
= ½ x 8 x (0.0050 ^ 2) * 100 = 0.01%
Hence, the bond price would be expected to increase by:
= 2.5% + 0.01% = 2.51%
or:
= 2.51% x 105 = 2.6355
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