Jeg kjenner ikke denne formelen, men det står følgende:
- XIRR expects at least one positive cash flow and one negative cash flow; otherwise, XIRR returns the #NUM! error value.
- If any number in dates precedes the starting date, XIRR returns the #NUM! error value.
- If values and dates contain a different number of values, XIRR returns the #NUM! error value.
- Excel uses an iterative technique for calculating XIRR. Using a changing rate (starting with guess), XIRR cycles through the calculation until the result is accurate within 0.000001 percent. If XIRR can't find a result that works after 100 tries, the #NUM! error value is returned. The rate is changed until:
where:
di = the ith, or last, payment date.
d1 = the 0th payment date.
Pi = the ith, or last, payment.
http://office.microsoft.com/en-us/excel-help/xirr-HP005209341.aspx
