How do I automatically calculate the difference between two dates?

[Assigned]

Before you yell, I know I am cross-posting, but I guess this question relates to both ASP and SQL.

I am building a database that users will update.
I have a table named "products".
Every product has a shelf life of 3 years and expires exactely at the end of the 3rd year.
Here is my table:
Productid ---- int
productName ---- varchar
manufacture_date ----- datetime default (getdate)
Expire_date ----- datetime

What I want is this, whenever a product is entered, the defualt date is the date the entry
was made. (I am using the "getdate") to automatically grab this.
BUT I also want the "Expire_date" field automatically calculated and then filled in.
That is, a user enters a product "manufacture_date" as 05/22/2003,
Then I want the expire field to be filled with 05/22/2006.
My preference is to handle this on the DB site and not ASP.

I am usings ASP and MS SQL 7.
Thanks,
assigned

[jofa]

DATEADD ( datepart , number, date ) ?

[jofa]

Is this nice or what?
Guess what the result from this is?
select dateadd(year, 3, '2004-02-29')


Exactly: '2007-02-28', not '2007-02-29' or '2007-03-01'