Your kneecap (patella) sits over the front of your knee joint. As you bend or straighten your knee, the underside of the patella glides over the bones that make up the knee. Strong tendons help attach the kneecap to the bones and muscles that surround the knee.
NETWORKDAYS.INTL(D3,E3,0000000) calculates whole days between the two dates (no weekends, no holidays). NETWORKDAYS(D3,E3,0000000,$A$16:$A$24) calculates whole working days days between the two dates (Sat/Sun weekends, holidays as per your list in $A$16:$A$24). Difference in non-working days between the two dates.
Alternately, remember Naegele's Rule. An easier way in figuring out due dates is to take the first day of your last period, count backward 3 months, add 7 days, and add an entire year. This is called Naegele's Rule. (Alternatively, to get the same result, you can take your LMP, add 1 week, and add 9 months.)