I just ran into someone having trouble making a custom formula in Microsoft Project. They were adding a duration to a date by using a + sign. For example:
[Finish1]+[Duration1]
The result they got was years in the future and was unexpected. The reason for this is that Duration is stored in minutes. The duration of an 8 hour day is 480. Dates, like Finish1, are stored as a serial number which is counting from 1/1/1900, making today 39842. When you add those two numbers together, each minute is treated as a day.
Fortunately MS Project has some functions which will do the date math for you. DateAdd will do simple date addition, and ProjDateAdd will do date addition with any of the Project calendars taken into account. If you have a duration of 5 days stored in the Duration1 field and today is Thursday, then the different functions would give the following results:
Now()+[Duration1] would give a date about 7 years from now.
DateAdd( "d", 5, now()) will give a date five days from today (Tuesday).
ProjDateAdd(Now(),[Duration1],"Standard") would give a date one work week
from today. (Thursday)
