use formula only if there is a blank cell

[demodren]

hi all, would anyone know how can I go about using a formula only if the cell is blank? I have thousands of rows and I need to use formula to lookup the value only if cell is blank? this avoid me using the formula for every single row where I already have static values.. I want to avoid filtering for blanks and then using the formula.. is there an easier way to solve this?

Any suggestions would be greatly appreciated

 

[bryonwoods30]

=if(cell="","",formula)

 

[demodren]

thanks Bryon.. but how do I tell it my starting point is A3 and goes all the way down to last row? I use the below to define last row:

LastRow2 = Cells.Find("*", [A1], , , xlByRows, xlPrevious).Row

how can I incorporate so it starts on A3 and goes all the way down to lastrow now?