T-SQL solution to find out how many weeks have passed between 2 dates.

I need a T-SQL solution to find out how many weeks have passed between 2 dates.
The week starts on a Monday and ends on a Friday.
So if the date was this Thursday and the new date is next Monday I need the answer to be 1.
In other words I do not need to be counting full weeks. This is necessary to change dates in multiple weeks of a project when a target date changes.
So if the target date is Thursday 2018/12/06 and it's changed to Tuesday 2018/12/18 my answer would be 2. (remember I do not count full weeks). Each instance passed a Monday is considered a week.  And I need it to start changing (adding the weeks) with the current weeks Monday. So if today was Tuesday 11/27/2018 these would be my old dates and new dates. (There are dates before the target date and after the target date).  

Original dates.                 New dates
M-11/26/18:F-11/30/18  M-12/10/18:F-12/14/18  
M-12/03/18:F-12/07/18  M-12/17/18:F-12/21/18   Target date
M-12/10/18:F-12/14/18  M-12/24/18:F-12/28/18
M-12/17/18:F-12/21/18  M-12/31/18:F-01/04/19
Chuck LoweAsked:
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ste5anSenior DeveloperCommented:
Well, it's imho simple, depending on the used SQL dialect, e.g. T-SQL:

SELECT DATEDIFF(DAY, DateFrom, DateTo) / 7 AS Weeks FROM yourTable;

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Vikas GargAssociate Principal EngineerCommented:

You can try this query

declare @from datetime= '9/1/2018'
declare @to datetime  = '9/17/2018' 

select datediff(day, -7, @to)/7-datediff(day, -6, @from)/7 MondayCount

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How many weeks passed two dates:
DECLARE @OriginalDate Date = '2018/12/06'
DECLARE @NewDate Date =  '2018/12/07'

SELECT DATEDIFF(week, @OriginalDate, @NewDate)

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So you can add  7 * DATEDIFF(week, @OriginalDate, @NewDate)  to all your existing date values and you should be fine.
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Chuck LoweAuthor Commented:
Exactly what I needed.

Just to clarify - what should be the result for date change from Monday this week to Friday next week?  1 week or 2 weeks?.
Chuck LoweAuthor Commented:
1 Week
Good. The accepted solution calculates this difference as 2 weeks:
declare @from datetime= '8/27/2018'
declare @to datetime  = '9/7/2018' 
select datediff(day, -7, @to)/7-datediff(day, -6, @from)/7 MondayCount

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