Calculate start date based on working hours and end date

Hello,

I need to calculate calculate required start date + time of a task based on task duration expressed in working hours and end date + time. I found formula to calculate number of working hours between 2 dates:

=(NETWORKDAYS(A2,B2,holidays)-1)*(J$3-J$2)+MOD(B2,1)-MOD(A2,1)

A2 = start time/date
B2 = end time/date
J2 = MF start time, e.g. 08:00
J3 = MF end time e.g. 17:00

However I need similar formula to calculate start date + time starting. Assume working hours from 8:00 to 17:00, duration is 13 hours and start date + time = 16/06/2010 9:00, then formula should return 14/06/2010 13:00. Note that formulate should also exclude weekends.

Is there anyone who can help?

Regards,

Kaatje

Hello,

Sorry mistake in my example description: Assume working hours from 8:00 to 17:00, duration is 13 hours and END date + time = 16/06/2010 9:00, then formula should return 14/06/2010 13:00 as start date. I need to calculate start date, does formula still count then?

Regards,

Kaatje