Help with Date Formula

[BigH]

Hi there,

Hopefully someone can help me, I have dates along a row, say from
column A out to column Z. The dates either stay the same or increase as
you move from column to column. i.e A1= 25 May, B1= 25 May, C1= 27 May,
D1= 29 May

I am looking to place a formula, two rows below, which looks at the
formula above and adds 13 days on to it, or 15 days or 17 days or 21
days, 23 days, 25 days. Only if the dates above are the same, and 13
days if the Date is different. i.e H1= 1 June, I2= 1 June, J1= 1 June,
K1 = 1 June, L1 = 1 June, M1 = 1 June

H3= 14 June, I3= 15 June, J3= 17 June and so on, the problem I have is
that the cell before has always got to have a lesser date than the cell
to the right of it. Sometimes this doesn't happen as the cell in N1= 5
June, then N3= 18 June, which is less than M3= 30 June

Is there any way I can get the formula on Row3, to say if the cell to
the left is greater than the date in the cell to the left (based on the
criteria above then add two days on to the cell on the right so that its
always greater than the cell to left of it?

hope this makes sense

BigH