Autofill based on date in non related cell?

Hi all

I know this is probably really basic but its doing my head in at moment!!!

I am creating a shift rota and have a worksheet for each month, in cell A1 of each worksheet i have the date, eg for April of next year =DATE(2012,4,1)

I want to display the days of the month across row 2, so in cell B2 i have =A1 formatted as dd in order to return the day, my limited knowledge tells me that cell B3 should be =A1+1 and then auto fill across for the rest of the month, however when i do this it only seems to copy no matter what i do, i've tried inserting $ symbols etc.

Any help most welcome

Thanks in anticipation.