PMBOK Process – What is a Projects Develop Schedule? 

 November 10, 2020

By  Dave Litten

PMBOK Process

What is the Develop Schedule?

Within the PMBOK, develop schedule is one of the largest of the 42 processes as it has 9 inputs, 10 tools, and 4 outputs. It uses the critical path method which in and of itself is one of the most important tools that you must understand fully for the PMP exam.

As you would expect that, the develop schedule process is where the schedule is created and uses the define activities, sequence activities, estimate activity resources, and estimate activity duration’s processes as its inputs:

The PMBOK Develop Schedule process inputs:

Activity list. This has been a common input for the previous processes that have been mentioned above and will have already been factored in, however he is an input that is implicitly used.

Activity attributes. Again, this has been a common input to the above processes, but because it contains extra information such as the individuals or knowledge, skills and experience required, along with their availability, it is an important input in order to create a realistic and achievable schedule.

Project schedule network diagrams. These were created in the sequence activities process and because this diagram shows the activity order, it is a key input here. Remember that the project schedule network diagram only shows the sequence and dependencies of the activities, but that the develop schedule process assigns start and finish dates to each activity.

Activity resource requirements. These were developed in the estimate activity resources process, and describe all human and non human resources that are required for each activity.

Resource calendars. These are vital as they show where resources are available and may constrain the timing, sequencing and dependencies of various activities and helps develop schedule.

Activity duration estimates. Another important input as the duration of each activity along with its dependencies will be used to develop the schedule.

Project scope statement. This was developed within the define scope process and is valuable because it contains assumptions and constraints for the project which will have a direct bearing on the activity schedule that is created here.

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Enterprise Environmental Factors. This may include aspects such how much risk is acceptable, or any laws or regulations that have an impact of the schedule.

Organizational Process Assets. These may include aspects such as policies, procedures or guidelines, or lessons learned from previous similar projects.

Develop Schedule outputs

Here are the six outputs from the develop schedule process:

Project schedule.

This was developed using the precedence diagramming method PDM), which was one of the tools used within the sequence activities process. However, the schedule now shows the plan to start and finish dates for each activity as well as the overall project. The project schedule is normally shown graphically and there are various different ways in which it can be shown:

Project network diagram.

This represents each activity as a rectangle within which key information is illustrated such as the activity name, its duration, its float or slack, and start and finish dates:

Bar Charts or Gantt Charts.

Each activity is illustrated as a bar or line whose length represents its duration and is listed against a suitable time line on the horizontal axis. The dependencies of each activity can be shown as well as other supporting information such as milestones, percentage complete and actual/planned start and finish times.

Because of the timeline is far easier to read and convey schedule information, and as such is often used as the preferred schedule graphic for communication and reporting aspects within the project.

Milestone chart.

A milestone is a zero DurationTask and is typically shown as stated diamond shape against a timeline much as by the Gantt chart diagram. Milestones often represent major products or deliverables or key events such as payment milestones, demonstrations, audits, presentations of the end of a stage or phase:

Schedule baseline.

By definition, and baselined whether cost, time, or scope, is the original approved plan plus any approved changes. When the develop schedule or activity is first used it will need to be approved either by the user, sponsor, customer, or operational/functional managers. Once approved it becomes the first to baselined the schedule.

Whenever a change is approved, the schedule is re-baselined and hence, will include the new changes. Old baselines are always kept as a reference point and are particularly useful when creating the end project report as they are an excellent source of the historical development of the various products and deliverables within the project.

Scheduled data.

This is the information which supports how the schedule was created and developed. If any schedule templates we used, then this would also be included here, although it could contain other information such as activities and their attributes, constraints and assumptions, and estimated durations. In short, any of the inputs used within this process.

Project document updates.

Any of the previous outputs from the preceding processes that lead to the creation of the project schedule may need to be updated here. In addition, risk and issue logs as well as resource calendars may need to be updated. One of the tools used in this process is resource levelling and is carried out to reduce peaks of resource usage as well as re-scheduling activities. As a consequence it is highly likely that resource requirements and their timing will be updated at this point.

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I shall now discuss the 8 tools that are used to develop the project schedule:

Schedule network analysis.

This actually refers to the set of techniques used to create the schedule and I will now explain each in turn:

Critical path method (CPM).

If you are familiar with this, then please refer to the next tool. For those who are not, then perhaps a simple example will illustrate the power and use of this method; suppose that you and a few friends are to meet me in a local bar after work at 5.00 PM. It is to celebrate my birthday and I want to buy you all a drink. I shall be there promptly at five, but because you and your friends will be arriving from different directions and distances, it is likely that you will arrive at different times. We cannot raise our glasses as a complete group until the last person arrives.

Put another way, the last person that arrives determines the earliest point in time that we can raise our glasses.

To relate this to a project, each person’s journey can be seen as a set of activities and dependencies within a project schedule. And the activity(s) that determine the last person to arrive, will set the project’s only just finish time and is called the critical path. Any delay or increase in duration of critical path activities will therefore cause the same delay to the project end-date.

Continuing with my birthday drink analogy, those who arrive before the last person have some time to spare before we raise our glasses. In a project, these represent activities that are non-critical, and the spare time is called slack or float.

Because of the schedule implications, critical activities are reviewed more regularly, and a project manager will want to put their most experienced staff of such activities. Because non-critical activities have some float or slack, then staff on these may be temporarily assigned to critical activities if they are incorrect of delaying, and also that non-critical staff may be those who are less experienced and can use to float or slack for rework.

Notice that all the above has little relevance to the project budget, only the schedule. The use of planning tools is helpful because they will automatically calculate and identify critical path activities and the float or slack of non-critical tasks.

Critical chain method.

This is a fairly new method and entails the use of buffers which are added to certain high risk activities as a way of ensuring that uncertainty is managed. As part of this approach the critical chain method uses ‘best case’ estimating. For effective use of this method, such buffers should only be known by the project manager and applied when appropriate. If the specialist team are aware of the buffers, then there is a temptation to use it up, and it will become a self fulfilling prophecy!

Resource levelling.

This is carried out after using the critical path method and observing the resource situation for all of the activities. After this first pass it is highly likely that there will be points in time where large amounts of resources are being used, and also that there may be point in time with the activity schedule needs more resources that are available.

Where high peaks of resource usage occurs within a schedule, problems can occur due to the management and logistics of these peaks and it will generally increased risk as a consequence. It is therefore best practice to see move such peaks out by moving non-critical activities within their float or slack to attempt to reduce the peaks. For obvious reasons this technique is called smoothing.

The second problem which may occur, is that there are not enough resources available at certain points within the schedule. This may be due to the amount of resources available, or which may be because our own individual resource is being passed to carry out more than one activity at a particular point in time.

Again, the first approach is to attempt to move non-critical tasks within their available float or slack to remove this over-allocation problem. If this is not possible, then an attempt should be made to reconnect each activity in terms of its predecessor and successor activities. If this does not resolve the problem, then it may be necessary to delay non-critical activities beyond their float or slack, all to delay critical path is activities, either of which will cause a delay to the end date of the project.

These should not necessarily be seen as a failure however, and management should see this as a realistic early finish date within the constraints of available resources. Another ploy may be two outsource certain activities were either extra resources are available, or where their specialist expertise and experience can be used to carry out the activity in less time.

Finally, if none of the above is satisfactory (for example win a fixed and mandatory end-date must be met), then it should be considered if the scope of the project, in terms of the deliverables or functionality, can be reduced given the resource constraints.

‘What if scenario’ analysis.

This uses a technique called Monte Carlo analysis and is performed by computer using huge numbers of simulated scheduling possibilities based on probable scenarios. A useful outcome of this technique is that it can predict schedule results as well as identify schedule risk areas. As the name suggests the and selecting likely scenarios, these in relation will predict the most likely outcomes along with potential risk areas.

Applying leads and lags.

This is a straightforward technique which concerns the relationships between won the activity and another. Put simply, a lag between one activity and another is a time delay. For example a successor activity will not start until a delay of, say, three days has occurred after the predecessor activity has finished.

An activity lead is the converse. Here, a successor’s activity can start before the predecessor has finished. Both of these have application in the real world, for example lags can be used when waiting for delivery of components (or for paint to dry!), and a lead can be used when it is not necessary to waits for all of the tasks by the activity to be completed before starting the next (an electrician could start installing the lighting even though the carpenter is still installing a kitchens fittings).

Schedule compression.

Previously, I have mentioned that reducing the project scope may be away of meeting a deadline end date. But there are two other techniques which can be used without reducing the scope and these are two methods of schedule compression.

Crashing the schedule.

This is simply adding more resources to key activities so that the work is completed quicker and their duration is reduced. If this is done for critical activities then this will result in an earlier finish to the project (can you see that reducing the duration of non-critical activities will have no affect on the project end-date although it may result in some activities starting earlier, and hence potentially resolving resource problems). Creating the schedule will often increase costs.

Be aware that some activities can only be carried out by one person, and also that the more people that are replied to an activity, the more complex the logistics and communication of the activity becomes. Typically, doubling the resources of an activity may only reduce the duration by a third.


This is done by changing the sequence and dependencies of the activities. The approach here is to consider which activities can be done wholly or partially in parallel rather than in series. If two critical activities of ten days in duration can be done in parallel rather than series, then you have potentially reduce the project end-date by 10 days.

Be aware that although fast-tracking does not normally increase costs, but it is highly likely to increase risk because of the simultaneous execution of activities. This may also give rise to resource over allocation problems.

Scheduling Tool.

There are many scheduling tools available, and probably the most popular is Microsoft project. Like all tools, it is only necessary to enter activity and resource information, and the tall will calculate schedule and resource requirements. Most tools allow you to carry out ‘what if analysis’ and either manually or automatically carry out levelling or smoothing.

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Dave Litten

David spent 25 years as a senior project manager for USA multinationals, and has deep experience in project management. He now develops a wide range of Project Management Masterclasses, under the Projex Academy brand name. In addition, David runs project management training seminars across the world, and is a prolific writer on the many topics of project management.

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