"Inchman" wrote:
Date cell is K4
[....]
Everything I try comes out with a "#VALUE!" error in the cell.
Here is one of the ways I tried it...
=IF(L4="Yes",K4+2465,K4+3560)
Note, K4 and M4 are both formatted as dates in the same configuration.

The problem is: Excel does not recognize the form of your dates.
Therefore, it treats them as text. The format does not matter (well, as
long as it is not Text).

For example, on my computer, Excel recognizes 2/15/2012 as today's date. If
I enter 15/2/2012, Excel treats that as text.

The Regional and Language control panel determines what Excel recognizes as
a date.

Alternatively, you can use the DATE function to enter dates unambiguously.
For example, DATE(2012,2,15).

Inchman wrote:
if L4 = "Yes" then I need to add 7 years
and 9 months to the date in K4. If not, I need it to
add 9 years and 9 months to the date in K4.

I don't know on what planet 2465 is 7 years 9 months, but I am pretty sure
that is not Earth time :-). Even 3560 is dubious. (I have not tried all
possible interpretations.)

I suggest that you use DATE(7+YEAR(K4),7+MONTH(K4),DAY(K4)).

Of course, that presumes that you fix your problem with K4 first.