Explanation
In the example, B6 is the hard-coded start date and the formula in B7 is:
=DATE(YEAR(B6),MONTH(B6)+1,DAY(B6))
To solve this formula, Excel first extracts the year, month, and day values from the date in B6, then adds 1 to the month value. Next, a new date is assembled by the DATE function, using the same day and year, and month + 1 for month.
=DATE(YEAR(B6),MONTH(B6)+1,DAY(B6))
=DATE(2010,1+1,15)
=DATE(2010,2,15)
=2/15/2010
The first formula therefore returns a new date of 2/15/2010, one month later than the starting date.
Once the first formula is entered, it is copied down as far as needed. Each subsequent formula creates a new date incremented by one day.
Note: if you start with a date like January 31, the formula above will skip February and move on to March. This happens because the new date, 2/31/2010 doesn't exist, so Excel uses the day value to roll forward to 3/3/2010, 3 days after the last day in February.
If you need a series of dates where every date is the last day of the month you can use EODATE like this:
=EOMONTH(B6,1)
