COUPDAYSNC(settlement,maturity,frequency,basis,eom)
settlement: settlement date
maturity: maturity date
frequency: number of interest payments per year
basis: calendar basis
eom: end-of-month flag
COUPDAYSNC calculates number of days from the settlement date to the next coupon period.
frequency may be 1 (annual), 2 (semi-annual), or 4 (quarterly). If basis is 0, then the US 30/360 method is used. If basis is 1, then actual number of days is used. If basis is 2, then actual number of days is used within a month, but years are considered only 360 days. If basis is 3, then actual number of days is used within a month, but years are always considered 365 days. If basis is 4, then the European 30/360 method is used.