Counting unique number of days in a data set

[George145]

I would be very grateful for any ideas or advice on the following conundrum:

I have approx. 600 line items of activities for a construction gantt chart, with Start and Finish dates.

. I am trying to count only the total number of "unique dates" (i.e. no overlaps) using a formula.

. Calculating the '23' in the below example is easy - simple SUM.

. Trying to also calculate the '19' in the below example which I can't solve...

Many thanks in advance!

George 

activity	start	finish	duration	overlap
Act-001	1 May 2021	10 May 2021	10
Act-002	7 May 2021	15 May 2021	9	4	(bec/ these already exist above)
Act-003	20 May 2021	23 May 2021	4
			23
				19	unique days

[#2]

@George145 Perhaps you can use the formulae demonstrated in the attached file. It calculates overlap as the duration between end dates for subsequent activities, only if the start date of the latest activity lays before the end data of the first. Otherwise, it returns zero.

[#3]

@Riny_van_Eekelen Thank you, but I don't think it will work if the start date on activities in the subsequent rows is earlier than the start date on activities in the preceding rows. Thoughts? 

activity	start	finish	duration	overlap	unique
Act-001	1-May-21	11-May-21	11	0	11
Act-002	4-Apr-21	8-May-21	35	-4	39
Act-003	9-May-21	23-May-21	15	0	15
			61	-4	65

[#4]

Sorry - I just reread the remainder of your note and you had already stated this constraint.