Today I will write about scheduling problems when you put the start and the end date
for tasks into MS PROJECT. I WILL NOT write about constraints and limitation with this method (for example about flexible and hard constraints and why this is not the best approach). I will just show you how duration is affected when you put those dates into MS PROJECT.
In MS Project 2010 you can choose between two types of scheduling: Manually or Automatic schedule. If you choose Manually you will have the whole control over the scheduling and you will not get the whole power of MS Project 2010. For my examples I’ve choose Automatic scheduling mode and it is shown on picture below:
Next we will set up daily, weekly and monthly working time:
And then:
We have told MS Project that regular working time will be Monday – Friday from 08:00 AM until 16:00 PM, 8 hours without lunch break.
Now we will set up our standard calendar:
1. Select Project TAB
2. Click on Change Working Time
3. On The For Calendar choose: Standard (Project) Calendar
4. Click on Work Weeks
5. Select Default
6. Click on Details
7. Select days: Monday – Friday
8. Choose: Set day(s) to these specific work times
9. Type 08:00 in From field and 16:00 in To field
10. On the same form click OK button
11. On the Change working time click OK button
Now you can enter two tasks: Task 1 with start on 22.3.11 and end on 22.03.11, and Task 2 with start on 22.3.11 and end on 23.03.11
What do I get? Task 1 has duration of 0,5 days, and Task 2 duration of 1 day. WHY?
Well it is easy to explain. When I put the same date for start and finish date for Task 1 I said: “I want my task to last 4 working hours”. WHY? Because I put in calendar options (from 08:00 till 12:00) that they will be a 4 hour job. And I also said that duration for one day is 8 hours. WHERE? See picture below:
So MS PROJECT calculates duration in formula 4 working hours / 8 hours per day in scheduling options = 0,5 days
For Task 2 I said that it will start on 22.3.11 and it will end on 23.3.11. Working time will be from 08:00 till 12:00 (4 hours), so it will be 2 days X 4 hours = 8 hours
And because the day duration lasts 8 hours (see picture above) MS PROJECT calculates duration in formula 8 working hours / 8 hours per day in scheduling options = 1 day
Now, suppose that in my calendar I choose the working time from Monday till Friday from 08:00 – 15:00 (7 working hours) and I put the same start and end date for Task 1 and Task 2 as I put before. Duration of Task 1 and Task 2 will be:
Task 1 has duration of 0,88 days, and Task 2 duration of 1,75 day.
Now, you know the duration formula, don’t you?
Duration of one day means 8 hours. We will work 7 hours on Task 1 (because we put that in the calendar; from 08:00 till 15:00). 7 working hours / 8 hours per day in scheduling options = 0,88 days.
For Task 2 we will work 7 hours on 22.03.11 and 7 hours on 23.03.11 so it means we will spend 14 hours in total. And 14 working hours / 8 hours per day in scheduling options = 1,75 days.
Now, suppose that in my calendar I choose the working time from Monday till Friday from 08:00 – 17:00 (9 working hours). Duration of Task 1 and Task 2 will be:
Task 1 has duration of 1 day, and Task 2 duration of 2,13 day. Duration of one day means 8 hours. We will work
8 hours on Task 1 (because we put that in the calendar; from 08:00 till 17:00). Something is wrong, isn’t it? From 08:00 till 17:00 is 9 hours and not 8. Well, yes it is. But you cannot work more than 8 hours per day if start and end date are the same because in scheduling options you said that you will have 8 hours
per day. So 8 working hours / 8 hours in scheduling options = 1 day.
For Task 2 we will work 9 hours on 22.03.11 and 8 hours on 23.03.11 so it means we will spend 17 hours in total. And 17 working hours / 8 hours in scheduling options = 2,13 days. You may ask yourself: “WHAT IS
WRONG NOW!??”.
Well, nothing is wrong. That is the way MS PROJECT works. If your start date is different from end date, MS PROJECT will respect working hours from calendar (in our example it is 9 hours / day) for first, second, third etc day EXCEPT last day (end date) which will last 8 hours (hours per day from scheduling options).
See you
So MS PROJECT calculates duration in formula 4 working hours / 8 hours per day in scheduling options = 0,5 days
For Task 2 I said that it will start on 22.3.11 and it will end on 23.3.11. Working time will be from 08:00 till 12:00 (4 hours), so it will be 2 days X 4 hours = 8 hours
And because the day duration lasts 8 hours (see picture above) MS PROJECT calculates duration in formula 8 working hours / 8 hours per day in scheduling options = 1 day
Now, suppose that in my calendar I choose the working time from Monday till Friday from 08:00 – 15:00 (7 working hours) and I put the same start and end date for Task 1 and Task 2 as I put before. Duration of Task 1 and Task 2 will be:
Task 1 has duration of 0,88 days, and Task 2 duration of 1,75 day. Now, you know the duration formula, don’t you? Duration of one day means 8 hours.
We will work 7 hours on Task 1 (because we put that in the calendar; from 08:00 till 15:00). 7 working hours / 8 hours per day in scheduling options = 0,88 days.
For Task 2 we will work 7 hours on 22.03.11 and 7 hours on 23.03.11 so it means we will spend 14 hours in total. And 14 working hours / 8 hours per day in scheduling options = 1,75 days.
Now, suppose that in my calendar I choose the working time from Monday till Friday from 08:00 – 17:00 (9 working hours). Duration of Task 1 and Task 2 will be:

Task 1 has duration of 1 day, and Task 2 duration of 2,13 day.
Duration of one day means 8 hours. We will work 8 hours on Task 1 (because
we put that in the calendar; from 08:00 till 17:00).
Something is wrong, isn’t it? From 08:00 till 17:00 is 9 hours and not 8. Well, yes it is. But you cannot work more than 8 hours per day if start and end date are the same because in
scheduling options you said that you will have 8 hours per day. So 8 working hours / 8 hours in scheduling options = 1 day.
For Task 2 we will work 9 hours on 22.03.11 and 8 hours on 23.03.11 so it means we will spend 17 hours in total. And 17 working hours / 8 hours in scheduling options = 2,13 days. You may ask yourself: “WHAT IS WRONG NOW!??”. Well, nothing is wrong. That is the way MS PROJECT works. If your start date is different from end date, MS PROJECT will respect working hours from calendar (in our example it is 9 hours / day) for first, second, third etc day EXCEPT last day (end date) which will last 8 hours (hours per day from scheduling options).
See you …..