Köszi az infot, ki fogom próbálni, hasznos függvény. Azért nem sima ügy ez a dátumosdi, pl. igen 1900-tól tud számolni, de azt is rosszul, legalábbis ha az 1900-as évvel is számolunk:

"...Excel behaves as if the date 1900-Feb-29 existed.  It did not.  The year 1900 was not a leap year (the year 2000 is a leap year).  In Excel, the day after 1900-Feb-28 is 1900-Feb-29.  In reality, the day after 1900-Feb-28  was 1900-Mar-1 .  This is not a "bug".  Indeed, it is by design.  Excel works this way because it was truly a bug in Lotus 123.  When Excel was introduced, 123 has nearly the entire market for spreadsheet software.  Microsoft decided to continue Lotus' bug, in order to fully compatible. .."

Ez innen:

http://www.cpearson.com/excel/datetime.htm