Excel - Sum of Open/Backlog end of each previous month

[emoes]

Hello, I'm looking for a way to calculate the backlog at the end of each previous month.
In the attached spreadsheet I have some example dates.

Column "A" Has the open / Start date and time (time is not important)
Column "B" Contains the Closing date OR is contains NO value when it is still open

I would like to Add in Column "H'the amount of open (No not closed in the previous month) numbers.
In the example, I would like to know in "H2" how many items are open of April 2017 at the first of May 1st 2017.
In "H3", I would like to know how many items are open of April 2017 AND May 2017 at the first of June 1st 2017.
In "H4", I would like to know how many items are open of April 2017 AND May 2017 AND Jun 2017 at the first of June 1st 2017. (Maybe all Items of April 2017 are closed in May, so not showing anymore)

All til March 1 2019.

I hoping for a formula instead of a Marco.

Thanks upfront to read my request and I'm hoping someone can help me out.

[Pepe Le Mokko]

Administrative note

Welcome to the forum

in your haste to solve your problem, you probably missed the yellow banner advising how to get answers faster by posting a sheet ?

Please take a moment to read it and attach a sheet accordingly.

Thanks you for helping us help you

[emoes]

Sorry, You are right.
I Made a mistake (the example file was to large and I didn't paid attention to the message hat the file was to large :-)

Thank you for the reminder.

Emoes