Forecasting Completion Date using NETWORKDAY.INTL and WORKDAYs

[MrCameronExcel]

Hi All,

I put together this forecast of completion dates to two towers below. I expect the completion date of the 2nd blocks to be the same in both OPTION 1 and OPTION 2 but they are slightly differing. Can anyone identify why and how to fix this? Thank you

	A	B
1	TASK	DURATION (DAYS) / DATE
2	TASK 1	5
3	TASK 2	6
4	TASK 3	7
5	Hotels	10
6	Rate of Uptake of Hotels	80%
7	Number of Flats (per tower)	200
8	Flats Requiring Hotel	=B6 * B7
9	Start Date 1st tower	03/07/23
10	Start date 2nd tower	04/03/24
11	Net Workdays between start dates of each tower	=NETWORKDAYS.INTL(B9, B10, 1)
12	OPTION 1 (use all hotels at 1st tower until it is complete): Est. completion of 1st tower	=WORKDAY(B9, (B8 / B5 * SUM(B2:B4))+(SUM(B2:B4)-(B5-1)))
13	OPTION 1 (use all hotels at 1st tower until it is complete): Est. completion of 2nd tower	=WORKDAY(B12, (B8 / B5 * SUM(B2:B4))+(SUM(B2:B4)-(B5-1)))
14	Approximate number of flats requiring hotel completed in first tower up until start of second tower.	=B11 / SUM(B2:B4) * B5
15	OPTION 2 (Once 2nd block starts, split the use of hotels between each tower until the 1st tower is complete, then all hotels at 2nd tower for remainder of work): Est. Completion of 1st tower	=WORKDAY(B10, ((B7-B14) / B5/2 * SUM(B2:B4))+(SUM(B2:B4)-((B5/2)-1)))
16	Net Workdays between Start of 2nd Block and Completion of 1st Block	=NETWORKDAYS.INTL(B10, B15, 1)
17	Approximate Number of Flats Requiring hotel Completed in 2nd block using half of HAFHs up until completion of first block	=B16 / SUM(B2:B4) * B5/2
18	OPTION 2 (Once 2nd block starts, split the use of hotels between each tower until the 1st tower is complete, then all hotels at 2nd tower for remainder of work): Est. Completion of 2nd tower	=WORKDAY(B15, ((B8-B17) / B5 * SUM(B2:B4))+(SUM(B2:B4)-((B5-1)))

 

[MrCameronExcel]

I have revised formulas in B14 and B17 as ROUND to use a whole number which has reduced the difference I am trying to solve, but it still isn't quite right.