Count of non-null columns in each row

I have a table that contains 4 columns and in the 5th column I want to store the count of how many non-null columns there are out of the previous 4. For example:

Where X is any value:

Column1 | Column2 | Column3 | Column4 | Count
  X     |    X    |   NULL  |    X    |   3
 NULL   |   NULL  |    X    |    X    |   2
 NULL   |   NULL  |   NULL  |   NULL  |   0

Answer

select
    T.Column1,
    T.Column2,
    T.Column3,
    T.Column4,
    (
        select count(*)
        from (values (T.Column1), (T.Column2), (T.Column3), (T.Column4)) as v(col)
        where v.col is not null
    ) as Column5
from Table1 as T