Posted by: Craig Harding | November 18, 2009

The Project Plan: Tasks & Time Estimates

The Project Plan: Tasks & Time Estimates

After you have completed the WBS and each deliverable has been broken down to the appropriate level, i.e., the level where the task can be completed within 40 hours or less, you are ready for the next steps in developing the project plan. (Please note, 40 hours or less is based upon best practice by PMBOK where hard deliverable tasks are kept to no longer than 1 week in duration.)

 The next step is to assign time estimates to each of the tasks.

After you have assigned time estimates, the next step is to put the tasks in logical sequence. Task dependencies will determine the sequence of some activities. The sequence of tasks is very dynamic. You must re-evaluate the sequence of tasks throughout the life of the project.

 You are now ready to:

  • Assign Human Resources – Consider the skill sets needed to perform the tasks.
  • Build a Project Schedule – Your will base your schedule on: when the project starts, how long each tasks takes, how many tasks are assigned to a resource, and the priority you assign each of those tasks. To do this

When you need to do Time Estimates

The time estimates are part of developing the project plan. They are started as early as possible in the planning process, often before the project manager has been assigned to the project. They should be completed as soon as possible after the WBS has been broken down into the lowest level. Completion and ongoing revision is the responsibility of the project manager.

 The Project Manager’s Role in Time Estimates

As Project Manager, you are responsible for refining any existing project time estimates, for assigning specific time estimates to each task in the fully decomposed WBS, and for revising and updating time estimates in the plan as the project progresses.

 How estimates are typically done

Task estimates are developed in 3 ways:

  1. Historical Information – some companies maintain project task plan templates containing pre-defined tasks for the specific product(s) being installed. The tasks are pre-estimated, based on experience from other implementations. Another source of estimates for tasks is previously used project plans.  Many project tasks, especially implementation project tasks, are repeatable and it is helpful to review how other project managers have estimated the tasks. (It is important to archive  your completed project plan in a common knowledgebase as part of your project closeout process. These estimates should be refined after specific resources (individuals) are assigned to perform the tasks.
  2.  For work units specific to the current project (e.g., an interface or a report), the PM can solicit estimates from an colleague or expert who has performed similar work in the past.
    If extensive work units are to be estimated (e.g., after a complex model is completed), the PM may request a technical resource to be assigned to the project specifically to perform the estimates.
    Other sources of Expert Judgement
    Individual project team members are also a good source of knowledge. They will often remember actuals from previous projects.
    Use Caution
    Be cautious of technical estimates made by functional resources or functional estimates made by technical resources. Both tend to undervalue the effort required by the other.
  3. Approved Estimating Algorithms – Spreadsheets containing formulas and estimating determinates may be available for estimating specific work units.
    Use Caution
    Before you use an estimating algorithm, make sure it is approved by the client sponsor or the PMO. An algorithm that fails to take the right factors into consideration can create big problems for your project.

Effort- vs. Duration-based Estimates

Most estimates are effort-based (i.e., the total effort or resource hours required to complete the task with no elapsed time factored into the estimate), but sometimes a duration-based approach is acceptable. For example, the time required to acquire workstation PCs is typically based on the vendor’s lead-time which is duration, rather than the number of resources applied to the task of PC acquisition. Therefore the acquisition task is duration (or elapsed time) based.

 Revising Estimates

You will need to revisit the initial time estimates once specific resources are acquired. Any estimates you use should be influenced by the capabilities of the individual assigned. The estimates found in the templates may assume an average skill and experience level, but the actual resource assigned may be a highly skilled resource with extensive experience. Such a resource will be capable of completing the work unit much quicker than the basic estimate. Conversely, an inexperienced, junior resource will require more time to complete the work. You should confer with the assigned resources to ensure that the estimates are as accurate as possible and to ensure that the resources can commit to estimates and will accept responsibility for completing the work within the estimated timeframe.
You may also have to make adjustments because of differences in the client situation.  As an example, maybe the current client has 5 resources available for analysis, while the typical client has only 1 resource. Pre-existing estimates are based on typical clients, so you would need to revise the estimate upward.

 Reconciling Estimates for New Project Managers

If you don’t have the subject matter expertise to reconcile a difference between the time estimate in a template or previous project plan and the one provided by the human resource assigned, what should you do?

  • Use the estimates provided by the assigned resource unless the resource makes adjustments to pre-existing estimates that seem unreasonable. 
  • If you sense that the adjustment might be out of line, use another source to confirm the resource’s estimate.  Possibilities include:
    • Looking back at previously used plans
    • Using one of the approved algorithms in conjunction with a historical estimate
    • Asking the PMO or a Project Manager with the subject matter expertise you lack is a good reality check.

 Skill in Estimating

As you become more skilled as a Project Manager, you will be able to refine estimates with greater confidence. The more experience you obtain with actuals vs estimates, the better your own judgment will become. Most implementation tasks are repeated project after project, so as you update your project plans, you will become more knowledgeable about how long tasks actually take.

Estimates Should Change Throughout the Project

Estimates can and should be changed as the project progresses and the team gains more knowledge about the work to be done. Completing significant tasks can provide information that invalidates early estimates for subsequent related tasks. For example, completing the functional design for an interface can indicate that too much time has been allocated for the development of the interface.

 General Acceptance requirements for Time Estimating

In summary, all time estimates should be based on the following criteria:

  • primarily be effort based (as opposed to duration based)
  • expressed in hours (not days)
  • based upon historical information, expert judgment, an approved algorithm, or a combination of all three
  • be agreed to by the resource assigned
  • take into consideration unique circumstances of the client and non-standard requirements specified in the SOW and Contract.

 Happy estimating,



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