Example: Find out
the duration of a bond if the interest 9.8% p.a. semi-annually for 4 year bond.
The coupon rate is 9% p.a. semi- annually. The face value of bond is Rs. 10,
000.
Solution: The
semi annual yield rate = 9.8/200 = 0.049
The semi- annual coupon rate = 9/200 = 0.045
The coupon payment = 0.045*10000 = Rs. 450
Year
|
Cash flows
|
Interest rate @ 4.9%
|
Present value of cash flows (C/ (1+r) n
|
Present value of cash flows * time
|
1
|
450
|
1.049
|
428.979
|
428.979
|
2
|
450
|
1.100
|
409.090
|
818.18
|
3
|
450
|
1.154
|
389.948
|
1, 169.844
|
4
|
450
|
1.210
|
371.900
|
1, 487.6
|
5
|
450
|
1.270
|
354.330
|
1, 771.65
|
6
|
450
|
1.332
|
337.837
|
2, 027.022
|
7
|
450
|
1.397
|
322.118
|
2, 254.826
|
8
|
10, 450
|
1.466
|
7, 128.240
|
57, 025.62
|
Total
|
9, 742.442
|
66, 984.021
|
= 66, 984.021 / 9, 742.442
= 6.875
= 6.875 / 2 = 3.437 years
Example:
Calculate the duration of 2 years bond whose face value is Rs. 10, 000. The coupon
rate is 7.6% per annum compounded quarterly. The yield rate is 8% per annum
compounded quarterly.
Solution:
Year
|
Cash flows
|
Interest rate @ 4.9%
|
Present value of cash flows (C/ (1+r) n
|
Present value of cash flows * t
|
1
|
190
|
1.02
|
186.274
|
186.274
|
2
|
190
|
1.040
|
182.692
|
365.384
|
3
|
190
|
1.061
|
179.076
|
537.228
|
4
|
190
|
1.082
|
175.600
|
702.4
|
5
|
190
|
1.104
|
172.101
|
860.505
|
6
|
190
|
1.126
|
168.738
|
1, 012.428
|
7
|
190
|
1.148
|
165.505
|
1, 158.535
|
8
|
10, 190
|
1.171
|
8, 701.964
|
69, 615.712
|
Total
|
9, 931.95
|
74, 438.466
|
= 74, 438.466 / 9, 931.95
= 7.464
= 7.464 / 4
= 1.873 years
Example: A 7 year
bond whose face value is Rs. 10, 000 and bears 9% coupon rate annually. Find
out the duration of bond if the yield rate is 9.8%.
Solution:
Year
|
Cash flows
|
Discount factor (1/1+r) n @ 4.9%
|
Present value of cash flows (C*(1/(1+r) n)
|
Weight (PV of cash flows / Total of PV
|
Weight*time
|
1
|
900
|
0.910
|
819
|
0.085
|
0.085
|
2
|
900
|
0.829
|
746.1
|
0.077
|
0.154
|
3
|
900
|
0.755
|
679.5
|
0.070
|
0.21
|
4
|
900
|
0.688
|
619.2
|
0.064
|
0.256
|
5
|
900
|
0.626
|
563.4
|
0.058
|
0.29
|
6
|
900
|
0.570
|
513
|
0.053
|
0.318
|
7
|
10, 900
|
0.519
|
5, 657.1
|
0.589
|
4.123
|
Total
|
9, 597.3
|
0.996
|
5.436 years
|
Example: A 10 year bond which bears 10% coupon rate
compounded half yearly. The face value of the bond is Rs. 10, 000. The yield
per annum is 10.8% compounded half yearly. The Macaulay duration is 6.44 years.
Find out the modified duration.
Solution: MD = Mac Duration / 1+ (ytm/n)
= 6.44 / 1+ (0.108/2)
= 6.11 years
Example: Mr. Mehta wants to know how much bond price changes
if the market rate decreases from 8% to 6%. The modified duration is 6 years
and the market price of a bond is Rs. 10, 230.
Solution: There is an inverse relationship between bond
price and interest rate. It means if interest rate decreases then the bond
price will increase. The modification duration helps to measure the changes in bond price in respect to changes in interest rate.
Modification duration = 6 year
Interest rate decreases by 2%
Then,
= 6*2
Bond price rises = 12%
Note: We can also calculate the duration of a bond by using
the weight of each present value of cash flows. If interest rate compounded
semi – annually, quarterly or monthly only time period will change and other
things remain the same in calculation. For example interest compounded
semi-annually time will be as 0.5, 1, 1.5, 2 etc
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