Using an actual 'check box' from the forms toolbar, you'll need to link the
checkbox to a cell somewhere (probably hidden, lets say Z1)
formula would be
=A1+0.05*Z1*A1
Note that each check box would need to be linked to a seperate cell.

If you're content to simply put an "X" in the cell, then you can use
=IF(B1="X",A1*1.05,A1)
--
Best Regards,

Luke M
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"juanpablo" wrote:

Hi,

I need to have an option (like a square selection box) on Column B, when the
square box is ticked, then the value adjacent needs to be multiplied by 5%,
if not selected then copy the same value.

A B C
1 100 (selected) 105
2 100 (not selected) 100
3