Excel 2007 : Leaving a cell with formula blank if the data cell is blank

Hi There,

I'm trying to create a cell that shows the 14 days from the start date I've tried =B1+14
with B1 being a date. That works perfectly however when I copy the formula down the column because there is no 'start date' this field automatically shows 14/01/1900.

Is there anyway that I can get the formula to only work when the date cell is populated ?

Thanks

Mark