Negative float in baseline schedule

Hi, richu.

I assume that the reason Ron says this is because having negative float in your baseline schedule means that your baseline plan is one that expects to finish the project later than your committed completion date. Why would a customer ever be comfortable with such a plan?

In general, any time that your baseline plan has negative float, either:

1. Re-planning should immediately be performed to compress the schedule and get rid of the negative float, or
2. Your plan should be re-baselined, always with the customer's/sponsor's approval, to change the committed completion date.

Of course, there should always be a working plan which includes a more aggressive schedule than the baseline, with the difference between the two plans representing schedule reserve.

Fraternally in project management,

Steve the Bajan

Agreed.

Negative float is generated from one of two sources:

1) You have out of sequence working (e.g. Activity B has started and has an FS predeccesor link from Activity A, which has not yet finished). This is an error in the baseline schedule and should therefore be corrected.

2) You have one or more constraints in your schedule which are not being satisfied (e.g. your project completion milestone has a "must finish by" constraint which is earlier than the milestone's early finish). This means either the constraint is incorrect (not a true constraint, is the wrong constraint type, or has the wrong date), or your schedule as it stands does not satisfy the requirements of the project.

A baseline schedule should always satisfy the requirements of the project, otherwise you are targeting failure.

(NB: I have seen one project where the contractor deemed the LD penalties of failing to achieve the contract comletion date to be lower than the construction costs he could save by planning to deliver it late, and hence deliberately and honestly submitted a baseline plan that did not satisfy the contractual completion date. This is a rare practise, and not one to be encouraged...)

Thanks Stephen & Gary,

I am preparing a baseline schedule , i have not assigned any constraints to any activities but still i am getting a few activities with negative floats. How do i overcome negative floats in a baseline schedule. I am working on Primavera P6.

Richu

Hi All

Asta PowerProject will not allow negative float after a reschedule.

You are forced to remove the constraints before the software will deliver the completion date.

Best regards

Mike Testro

Richu,

Do you have a constraint at the project level (from EPS, highlight project, View > show on bottom > tick "project details", then go to "dates" tab of the project details and check the "must finish by" box)?

Do you have any actual progress on your baseline schedule?

If the answer to both of the above is "No", I am not sure why you are getting negative float. It may be a calendar issue or a starnge relationship, perhaps with negative lag.

Best thing to do in such a situation is to try and trace the path of negative float through the project, and check for anything strange on each activity.

Good luck,

G

Hi Gary

Another possibility is "fixed end date" on the project data.

Best regards

Mike T.

The most likely reason for negative float in a P6 schedule that “has no constraints” is External Early Start and/or External Early Finish constraints.  They will not show up in the constraints area of the activity tabs, so don’t look for them there.  I suggest displaying their columns and then sorting on them to find them.  Good luck!

Ronald,

Thank you for the timely help.

The problem was due to 'External Early Finish' constraint. I don't understand from where, when & how this constraint has into schedule.

After i have removed the 'External Early Finish'  dates & the negative floats are gone.

Thank you all.

Richu

Hi

The most easiest test is to reduce the duration of the activity corresponding to the (-)tive float , it must be come zero, if not then go through any or all the replies

Cheers

Hi All

External Early Start Dates and External Late Finish Dates are imposed as constraints on an imported program (XER file) that had relationships to one or more other programs in its original database.

Each inter-program relationship is constrained in this way, the software is trying to honour the logic to the other programs which no longer exist when you import the program.

Unfortunately the software does not make this clear or apparent in any way when you are importing the XER file - you have to go looking for it.

The easiest way to find these is to insert two columns for External Early Start and External Late Finish. You can the delete the dates in these columns and this will remove the constraints.

It would also be worth checking to see what these inter-program relationships represented as you may need to re-create this logic somehow in the imported program.

Primavera P6 has a number of counter-intuitive features such as this. I recommend Paul Eastwood Harris' training manuals for Primavera P6 which outline this and many other Primavera 'quirks' that need to be understood to avoid programming errors.

Regards

Alex

Alex,

Thank you Alex for the knowledge sharing.

It was quite helpful to me.

Regards,

Richu