>>You can have a computed field in your table (and add an index on this field).
>>
>>Field's definition will be
>>

>>dateadd(day, NumberOfDays, AddDate)

>>
>>Then, using this new field, you can write queries such as
>>

>>declare @Today date -- SQL Server 2008
>>
>>set @Today = cast(getdate() as date)
>>
>>select * from myTable where FutureDate < @Today

>
>Thanks, this is good. But, I need to avoid creating additional field or computed field in the table.

If so, you may try

select * from myTable where AddDate < dateadd(day,-1 * NumberOfDays, cast(getdate() as date)

-- assuming your AddDate field is indexed