Apple Numbers '08 - Manual (Page 223)

Chapter 12 Dictionary of Functions 223
2 uses actual/360 (calendar days for each month but 360 days per year).
3 uses actual/365 (calendar days for each month but 365 days per year).
4 uses 30E/360 (European 30/360).
COUPNUM
The COUPNUM function counts the coupons to be paid for a security between the
settlement date and the maturity date.
COUPNUM(settle, maturity, frequency, [day-count])
 settle: The date of the settlement, usually the date when the security was purchased.
 maturity: The date the security matures (expires).
 frequency: The number of coupon payments each year.
1 means annual payments.
2 means semiannual payments (twice per year).
4 means quarterly payments (four per year).
 day-count: Optional; specifies the number of days per month and days per year used
in the calculations (sometimes called the day count basis).
0 or omitted uses 30/360 (30 days for each month, 360 days in a year).
1 uses actual/actual (the number of days shown on a calendar).
2 uses actual/360 (calendar days for each month but 360 days per year).
3 uses actual/365 (calendar days for each month but 365 days per year).
4 uses 30E/360 (European 30/360).
Examples
If A1:A4 contain 9/1/2000, 1/1/2001, 4, 1:
COUPDAYSNC(A1, A2, A3, A4) returns 30 (the number of days from September 1 to the next coupon
date, October 1, on the basis of 30 days in September).
COUPDAYSNC(DATE(2000,8,1), A2, A3, A4) returns 61 (the number of days from August 1 to the next
coupon date, October 1, on the basis of 31 days in August and 30 days in September).
COUPDAYSNC(DATE(2000,8,1), A2, A3, 0) returns 60 (the number of days from August 1 to the next
coupon date, October 1, on the basis of 30 days in August and 30 days in September).