A	B	C	D	E	F	G	H	I	J	K	L	M	N
2
3		DiffY
4
5		Category:	Date and Time Calculations
6		Family:	Date Difference
7		Arguments:	Date1, Date2, [DayCount], [Periods]
8		Meaning:	Difference in Years
9		Description:	Calculates the difference in years between two dates as Date2 - Date1
10
11						Date1	15 Jan 01	15 Jan 01	15 Nov 99	1 Apr 01	29 Feb 00
12						Date2	30 Mar 01	31 Mar 01	12 Jan 00	15 Jan 01	15 Jan 09
13							74	75	58	(76)	3243
14									0.1588
15							DiffY	DiffY	DiffY	DiffY	DiffY
16		DCount					Function	Function	Function	Function	Function
17			Actual Days/Actual Days In Month ('Decimal Year').				0.2083	0.2111	0.1583	(0.2111)	8.8750
18
19			30/360 (PSA).				0.2083	0.2111	0.1583	(0.2111)	8.8750
20		1	Actual/Actual (365 or 366).				0.2027	0.2055	0.1588	(0.2082)	8.8772	8.8772 *
21		2	Actual Days/360.				0.2056	0.2083	0.1611	(0.2111)	9.0083
22		3	Actual Days/365.				0.2027	0.2055	0.1589	(0.2082)	8.8849
23		4	30/360 (European).				0.2083	0.2083	0.1583	(0.2111)	8.8778
24		5	Actual Days/Actual Days In Month ('Decimal Year').				0.2070	0.2097	0.1573	(0.2124)	8.8738
25
26		Check: First Principles:
27			30/360 (PSA).				0.2083	0.2111	0.2111	(0.2111)
28		1	Actual/Actual (365 or 366).				0.2027	0.2055	0.1589	(0.2082)
29		2	Actual Days/360.				0.2056	0.2083	0.1611	(0.2111)
30		3	Actual Days/365.				0.2027	0.2055	0.1589	(0.2082)
31		4	30/360 (European).				0.2083	0.2083	0.2111	(0.2111)
32
33		5	Actual Days/Actual Days In Month ('Decimal Year').				0.2070	0.2097	0.2124	(0.2124)
34
35		Excel's YEARFRAC function:
36			30/360				0.2083	0.2111	0.1583	0.2111	8.8750
37		1	ACT/ACT				0.2027	0.2055	0.1589	0.2082	8.8776	8.8776 *
38		2	ACT/360				0.2056	0.2083	0.1611	0.2111	9.0083
39		3	ACT/365				0.2027	0.2055	0.1589	0.2082	8.8849
40		4	30E/350				0.2083	0.2083	0.1583	0.2111	8.8778
41
42		Note on Date Inclusivity:
43		The Business Functions Library (and Excel's YEARFRAC) function include the Start date but Exclude the Finish Date.
44		In other words, all these functions are not Date inclusive.
45
46
47							* Note that BF and Excel use different methods where the time difference spans
48							a leap year.  Excel uses the average number of days in the years between the start year
49							and end year, irrespective of where the start date and end date are.
50							BF counts the number of whole years (in this case 8) and adds the fractional part in the
51							366-day year to that of the 365-day year, in accordance with bond calculation methodology
52							(source: Krgin, Handbook of Global Fixed Income Calculations).
53							In fact, the behavour of ACT/ACT for periods longer than a year is not standardised - bonds
54							are only concerned with periods of less than a year.
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