Rolling week numbers into one row and getting cummulative values
create table orders(id int identity, dt_created date);

insert into  orders (dt_created) values
('20180101'),('20180108'),('20180109'),('20180110'),('20180112'),
('20180113'),('20180114'),('20180115'),('20180116'),('20180117'),
('20180118'),('20180120'),('20180121'),('20180122'),('20180123');
GO



15 rows affected






SELECT
    DATEPART(WK, dt_created) week,
    COUNT(*) CT
FROM
    orders
GROUP BY
    DATEPART(WK, dt_created)
GO



week | CT
---: | -:
   1 |  1
   2 |  5
   3 |  6
   4 |  3



Have a look at OVER clause and how to get a cumulative total.



WITH WK AS
(
SELECT
    DATEPART(WK, dt_created) week,
    COUNT(*) CT
FROM
    orders
GROUP BY
    DATEPART(WK, dt_created)
)
SELECT
    week,
    SUM(CT) OVER (ORDER BY week) total
FROM
    WK;
GO



week | total
---: | ----:
   1 |     1
   2 |     6
   3 |    12
   4 |    15



db&lt;>fiddle here