sql server - SQL 2012 - Query to return month number

Question

I need to return the month number for a given date. For the current month, the month number would be 0. For the following month, the MonthNo would be 1. The previous month would be -1, 2 months ago would be -2. etc So assuming today is 16 June 2020, see example data below:

IF OBJECT_ID('tempdb..#DateTest') IS NOT NULL
    DROP TABLE #DateTest

CREATE TABLE #DateTest
(
DateTest Date
)

INSERT INTO #DateTest
VALUES
('23/08/2020'),
('14/06/2020'),
('01/06/2020'),
('15/05/2020'),
('01/05/2020'),
('18/01/2020') 

Select * FROM #DateTest

I would need to return the below:

Date          MonthNo
23/08/2020    2
14/06/2020    0
01/06/2020    0
15/05/2020    -1
01/05/2020    -1
18/01/2020    -5

Is there any way to return this info?

Answer 1

Looks like ordinary DATEDIFF, it should work for you:

SELECT 
  DateTest AS [Date],
  DATEDIFF(MONTH, GETDATE(), DateTest) AS [MonthNo]
FROM #DateTest

Demo