BTW: Again - Only because I searched and searched for a simple example solution and could not find, I hope this might be helpful to new starts. Used Praveens take on it as base but changed it up a bit so i could understand what was happening. I break things down into smaller simpler parts. Would love a more efficient way, pointers welcome.
UPDATE (1/11/2020): corrected minor issue with calculation, adjusted to span 12 months with possible overlap BUT just one year max. Hope that makes sense. This really does seem SUPER inefficient - there has to be a better way to do this simple calc.
How to calculate difference between dates excluding weekends:
IFS(
AND(
ISNOTBLANK([START DATE]),
ISNOTBLANK([END DATE]),
(HOUR([END DATE]-[START DATE])/24)>7
),
IF(YEAR(DATE([END DATE]))>YEAR(DATE([START DATE])),
IF(((WEEKNUM(DATE([END DATE]))+52) - WEEKNUM(DATE([START DATE])))<2, 0, ((WEEKNUM(DATE([END DATE])) +52)- WEEKNUM(DATE([START DATE]))-1)*5)
, IF((WEEKNUM(DATE([END DATE])) - WEEKNUM(DATE([START DATE])))<2, 0, (WEEKNUM(DATE([END DATE])) - WEEKNUM(DATE([START DATE]))-1)*5))+
IF(
IN(
WEEKDAY([START DATE]),
LIST(2,3,4,5,6)
),
SWITCH(WEEKDAY([START DATE]),2,5,3,4,4,3,5,2,6,1,0),
0+
IF(
IN(
WEEKDAY([END DATE]),
LIST(2,3,4,5,6)
),
WEEKDAY([END DATE]) -1,
0
),
(HOUR([END DATE]-[START DATE])/24)<15,
IF(
WEEKDAY([END DATE]) > WEEKDAY([START DATE]),
(HOUR([END DATE]-[START DATE])/24)+1,
SWITCH(WEEKDAY([END DATE]) -WEEKDAY([START DATE]),-4,2,-3,3,-2,4,-1,5,0,6,1)
)
)