=IF(C5=""; "" ;C5+30)

Explanation detail
if ([logical test] c5 equals ""; then [result if true] ""; else [result if
false] c5+30)

Explanation brief
if c5 equals "" then "" else c5+30
HTH
Erasmus



"Lando" a écrit dans le message de news:
...
I try to make function for due payment. When I made copy file and then drag
down the formula and it's succed. But for the cell that I not fill yet has
due date also.
How to make that cell became 0 (zero) if not fill the cell yet.

example :

A1 A2
19/8/05 =A1+30
- 30/01/00
- 30/01/00

Thanks

Lando