declare @StartDate date = '20120101',
        @EndDate date = '20121230',
        @Interval int = 2;

with e1(n) as (select 1 from (values (1),(1),(1),(1),(1),(1),(1),(1),(1),(1))dt(n)), -- 10 rows
     e2(n) as (select 1 from e1 a cross join e1 b), -- 100 rows
     e4(n) as (select 1 from e2 a cross join e2 b), -- 10,000 rows
     eTally(n) as (select row_number() over (order by (select null)) from e4 a cross join e2 b) -- 1,000,000 rows
select top ((datediff(dd, @StartDate, @EndDate) + @Interval + 1)/(@Interval + 1))
    dateadd(dd, (1 + @Interval) * (n - 1), @StartDate)
from
    eTally

DECLARE  @Fromdate  DATE = '01 Jan 2012'
        ,@Todate    DATE = '30 Dec 2012'
        ,@Interval  INT = 2

SELECT DateC , N
FROM (  SELECT DATEADD(DAY, N, @Fromdate ) AS DateC, N
        FROM  (SELECT (ROW_NUMBER() OVER (ORDER BY [object_id]) - 1) * (@Interval + 1)
               FROM sys.columns) dt(N)
     ) R
WHERE DateC <= @Todate