|When you say "List for someone to select = T+1. T-0, T-1 etc..." do you mean a Data Validation Drop Down List?|
If so, something like this might work.
Column A contains the values for your Drop Down List
Column B contains your launch date
Column C contains the actual Drop Down
Column D contains the formula shown
For T-2, the formula will return 2/2/2014.
A B C D
1 T-2 2/16/2014 T-2 =RIGHT(C1,LEN(C1)-1)*7+B1
Note, if the "T" values will always be a single digit, then you can use this:
Using the LEN function as above allows for any value, such as 20, 137, etc., as long as the value doesn't result in an invalid date.
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