How to update Project Calendar & Keep Start / Finish Dates the same

Copper Contributor

I created a new schedule and set the durations to give me the correct Start and Finish Dates, however I forgot to change the calendar at the beginning from the standard default, which is 5 days a week. I need to change the calendar to 7 days a week without altering the start and finish. How can I update the calendar to increase the durations and not the Start / Finish Dates?

4 Replies


It kinda sounds like you want to do the schedule instead of letting Project do what it does best. Hopefully you are NOT also using manual scheduling. If you are then why use Project, Excel would be easier.


But to answer your question, how did you enter the duration values, hours or days? If your 7 day workweek calendar still has the default 8 hour workday (8:00 AM to 5:00 PM with 1 hour lunch break), then adding the 2 extra days will effectively add 2 days or 16 hours which you will have to add to each duration value. If you have custom work hours in your 7 day calendar, then you will have to add the appropriate amount.


You will have to do all this manually, there is no setting that will automatically make the adjustment for you.


Hope this helps.


The duration values are days. Most of these tasks are already complete, this schedule includes a lot of retroactive tasks I've added to represent projects that have already been completed. The dates are correct, except It would be nice to be able to see the true durations. I don't see why if task is set to 100% complete and then update the calendar for said activity, then it should update the duration, but instead it doesn't do anything. Or the ability to constrain all said task start / finish dates then update calendar which would then only have one option but to alter durations.
Here's the why. You can't change history. When a task is done, it's done.

But here's something you can try. First, re-set the Project calendar to the 7 day workweek. Second, zero out the Percent Complete field. Third, update the duration by 2 days. The start and finish dates should remain the same. Finally, enter 100% into the Duration field.

If resources are assigned to the tasks, the above process needs to be modified or you'll end up with some incorrect data.






In response your request to keep the scheduled dates after changing project calendar, you can try this experimental procedure, following the steps below:


In the initial project file, and before changing the calendar from 5 to 7 days


  1. Make backup copy of the file
  2. Establish a baseline that is free, such as Baseline 5, for example, which will serve as visual reference in the Gantt, by selecting: (Menu / Project / Schedule / Establish Baseline...Entire project, and OK)
  3. Select Baseline 5, in: (Gantt Chart Format / Bar Styles / Baseline)
  4. Hide, if not already, the Project Summary Task, in: (Gantt Chart Format / Show or Hide)
  5. Shows, if not, the column % Complete
  6. Insert a column of a custom text field into the table, such as Text1, for example
  7. Copy column % Complete to Text1
  8. Copies at the same time to the clipboard (memory), the contiguous columns, Start  and Finish
  9. Modify your calendar from 5 to 7 working days per week
  10. Select all the tasks of the project (click upper left corner of the table)
  11. Select these three options at once: Percet complete = 0%, Duration = 0 day, and Schedule Mode = Manually Scheduled; in the General tab, through: (Menu / Task / Properties / Information, and OK)
  12. Pastes the Start and Finish columns from the clipboard (in memory), onto those columns
  13. Copy and Paste the column Text1 in % Complete
  14. Select all tasks of the project (click upper left corner of the table)
  15. Select Auto Schedule option, in Menu / Task / Tasks


Note.- It must be manually adjusted, increasing or reducing the lag of the links other than 0 days, when the successor task does not coincide with the initial dates of the 5-day calendar.


Select: Baseline 5, under Gantt Chart Format / Bar Styles / Baseline, to hide the Baseline 5 bar on the Gantt.


Note: Other variables such as Task type, other Constraints date, Task calendars, Resource work, Costs, etc. could influence the result sought, and would require a more exhaustive analysis.


I hope you find it useful.


Ignacio Martín