A few corrections: Replace "Basis: [optional] indicates how the year is to be treated; see section 3.11.6" with "Basis: [optional] indicates the day count basis to use; see section 3.11.6" Replace "Constraints: If settlement date or maturity date is not valid, INTRATE returns an error." with Constraints: Settlement < Maturity From Semantics remove "If the Settlement date is equal to or after the maturity date, an Error is returned." And add the formula: The return value for this function is: ( (Redemption- Investment)/Investment ) / YEARFRAC(Settlement; Maturity; Basis)