Author : Skon Lapamnuaypol, PMP
Have you ever received the advice from your boss or manager that “To meet the schedule, you have to start with the deadline and work backwards, so we can meet the target date?” Does this message make sense? In other words, is this a scheduling management technique to make a project meet its deadline?
In the real world, projects need resources, time, and activities to complete project works within a planned target date or schedule. Leaving such constraints untouched, the schedule will never be changed. It sounds like this message is not valid in the real world. Yet in reality the answer is “not really”, because there are no underlying assumptions and constraint factors. Let’s review the technique, which is available in the project management practice and PMBOK, which can be applied to this case.
Actually, in a scheduling tool, like Microsoft Project, there are two scheduling techniques available. These are the forward scheduling and backward scheduling techniques. Forward scheduling is pretty much familiar to most project managers or people who manage projects. The concept is simply to just identify the start date of a project, and to subsequently identify respective tasks with dependencies and other constraints. The scheduling tool will automatically calculate the earliest start, the float and the present in a Gantt chart or Network Diagram format.
In the contrary, with backward scheduling, the finish date is set first and the scheduling tool will calculate the latest start instead of the earliest start and will draw the Gantt chart. The following picture demonstrates a sample of forward and backward scheduling in Microsoft Project.
We understand that forward scheduling is the way to answer “when a project will be completed, based on a start date,” while backward scheduling will tell us “when we should start the project in order to meet the target date.” These are the fundamentals of a scheduling technique.
The following Gantt charts are sample projects to demonstrate the scheduling estimation based on forward and backward scheduling techniques. The number of tasks, work duration and dependencies of these two charts are identical. An additional constraint that we put in task No. 5 and task No. 8 is a resource dependency. The two tasks need the same resource (“Peter”) to complete the project works.
The chart demonstrates clearly that both scheduling technique will need the same period of time (15 days) to complete the project. Assuming that the project owner wants the project to complete on 14-Jun (and to date is 3-Jun), how the project manager should response is as follows:
- With the constraints as described above, if the project start on 3-Jun, it will need 15 days to complete, which is on 21-Jun (from forward scheduling calculation);
- If we need the project to be completed on 14-Jun, the project should at least start on 27-May, for which 15 days duration is required (from backward scheduling calculation).
Both answers may not satisfy the project owner. The next question that might be raised is “what else can be done to make this project meet the target date (14-Jun)?” Based on PMBOK, there are two ways to optimize the project schedule. These are:
- Crashing: A technique used to shorten the schedule duration for the least incremental cost by adding resources. Examples of crashing include approving overtime, bringing in additional resources, or paying to expedite delivery of activities on the critical path. Crashing works only for activities on the critical path, where additional resources will shorten the activity’s duration. Crashing does not always produce a viable alternative and may result in increased risk and/or cost;
- Fast tracking: A schedule compression technique in which activities or phases normally done in sequence are performed in parallel for at least a portion of their duration. An example is constructing the foundation for a building before completing all of the architectural drawings. Fast tracking may result in rework and increased risk. Fast tracking only works if activities can be overlapped to shorten the project duration
Let’s apply crashing and fast tracking technique into the sample cases demonstrated above. From the sample schedules, we will add more resources in order to shorten tasks 2, 5, 8 and 7. For the backward scheduling sample, after we add more resources, the start date is still not valid (start date is before today’s date – 3-Jun). We can optimize further on this schedule as there still is slack time (underline in Gantt chart). By shifting tasks 6, 7 and 8 to start earlier (start on earliest start date), the schedule will be the same as in the forward scheduling case. The following are Gantt charts for the schedule crashing sample:
Fast tracking is another schedule optimization technique to allow tasks to be performed in parallel. In this technique task dependencies need to be removed or optimized. For our sample, the new resource (Robert) who has the same skill set as Peter is assigned to task 8. So, tasks 5 and 8 can be performed in parallel. Assuming that we can start task 4 and task 5 with 1 day lead time from the predecessor task finished date, the tasks will be overlapped at the end of the predecessor task. As the Gantt charts samples below show, the project schedule will meet the project owner’s expectation.
The schedule crashing and fast tracking techniques can be applied together to the schedule, depending on additional resources and task dependencies.
Let’s come back to the question whether “can backward planning make a project schedule meet the deadline?” From the sample cases that we explored above, working backwards or backward scheduling alone will not be able to optimize the schedule. Crashing or fast tracking the schedule or applying both can help optimizing the project schedule. These two techniques can be applied to both forward and backward scheduling. However, with reference to the triple project constraints (scope, cost, and schedule), adding more resources or having resources work overtime will incur more cost to the project. So, the project owner has to agree and approve not only the schedule revision (reduction), but also need to approve the addition cost for optimizing the schedule. However, the techniques as provided by PMBOK make it possible to deliver the project within the timeline as required by the project owner.
Note: Definition of Crashing and Fast Tracking are excerpted from PMBOK 5th edition.
Skon Lapamnuaypol is a PMP certified project manager with a Bachelor degree in Computer Science from Chiang Mai University. He has proven 20 years
experiences in IT industry, which includes 14 years’ experience managing IT Implementation Projects in Banking, Manufacturing and Retail Industries. On Technology area, Skon has strong knowledge and background on Software Engineering, Software Development and System Integration.