Format cell based on date

[Arthur]

I want to highlight some cells based on a repeating sequence of days.

For example:

Column A2 = 1/1/2009 so I want to highlight (fill) cells G2 and H2 and
repeat that every 21 days (1/22/2009, 2/12/2009 etc)

Column A5 = 1/4/2009 so I want to highlight (fill) cells C5 and D5 and
repeat that every 21 days (1/25/2009, 2/15/2009 etc)

etc

I already have other conditional formats applied to the cells that will
validate and change the color of the text entered if it isn't within a
certain range, and they work great. Now I need to basically set a schedule of
events based on # of days from a given staring point. Think of it as a
maintenance schedule for which I want to highlight the particular event for
that day (repeated every 3 weeks)

 

[Fred Smith]

Your requirements are not clear to me, but maybe this will help.

If you have a starting date in A2, then
=a2+21
will give you the date 21 days later.

If you want to determine whether two dates are a multiple of 21 days apart,
you can use:
=mod(g2-a2,21)
This will equal 0 when the two dates are multiples of 21 days apart.

Regards,
Fred.