Accurate time estimation is a skill essential to good project management. It is important to get time estimates right for two main reasons:

1. Time estimates drive the setting of deadlines for delivery of projects, and hence peoples' assessments of your reliability
2. They often determine the pricing of contracts and hence their profitability.

Usually people vastly underestimate the amount of time needed to implement projects. This is true particularly when they are not familiar with the task to be carried out.                                      

They forget to take into account unexpected events or unscheduled high priority work. People also often simply fail to allow for the full complexity involved with a job.

Time estimates are important inputs into the other techniques used to organise and structure medium and large sized projects (Gantt charts and use of Critical Path Analysis). Both of these techniques reduce large projects down into a set of small projects.

Fully understanding the problem to solve
The first stage in estimating time accurately is to fully understand what you need to achieve. This involves reviewing the task in detail so that there are no unknowns. Inevitably it is the difficult-to-understand, tricky problems that take the greatest amount of time to solve.

The best way to review the job is to list all tasks in full detail.

Estimating time
You can only start to estimate time accurately when you have a detailed list of all the tasks that you must achieve. When you have this, you can make your best guess at how long each task will take to complete.

Ensure that within your estimate you also allow time for project management, detailed project planning, liaison with outside bodies, meetings, quality assurance and any supporting documentation necessary.

Also make sure that you have allowed time for:

• Other high urgency tasks to be carried out which will have priority over this one
• Accidents and emergencies
• Internal meetings
• Holidays and sickness in essential staff
• Contact with other customers, perhaps to arrange the next job
• Breakdowns in equipment
• Missed deliveries by suppliers
• Interruptions

• Quality control rejections

These factors may double (or more than double) the length of time needed to complete a project. If the accuracy of time estimates is critical, you may find it effective to develop a systematic approach to including these factors. If possible, base this on past experience.

Key points:

You can lose a great deal of credibility by underestimating the length of time needed to implement a project. If you underestimate time, not only do you miss deadlines, you also put other project workers under unnecessary stress. Projects will become seriously unprofitable, and other tasks cannot be started.

The first step towards making good time estimates is to fully understand the problem to be solved. You can then prepare a detailed list of tasks that must be achieved. This list should include all the administrative tasks and meetings you need to carry out as well as the work itself.  

Finally, allow time for all the expected and unexpected disruptions and delays to work that will inevitably happen.

Estimating time taken on complex projects

Where you need to carry out a complex project in which resources are limited or performance of one task is dependent on completion of another task, then techniques such as Critical Path Analysis can be useful. Time estimates for each stage should allow for unpredictable events as described above.

Scheduling Simple Projects

Simple projects involve only one or a few people over a short time. Typically, simple projects will have few tasks dependent on other tasks, and will be relatively simple and easy to coordinate. Examples might be coordinating delivery of resources for a workshop session, implementing a small marketing plan, or delivering a simple software enhancement.

With simple projects, tools like Gantt Charts and Critical Path Diagrams may overcomplicate project scheduling and communication. Unless project team members are trained in their use, they can often 'blind people with science', leading to poor communication and muddled projects. Appropriate Timetables and Action Plans are often sufficient to coordinate and implement simple projects. These should be explained and negotiated with project staff to improve the plans and get staff understanding, input and buy-in.

It will often be enough to create a workback schedule, starting from the date by which the project must be completed, and listing all of the tasks in reverse order with due dates for each.

Key points:

Simple projects are often best run using simple Timetables and Action Plans. These should be prepared and negotiated with project staff to improve plans and get buy-in. During the project these will contain sufficient control points and deliveries to monitor project progress and take any appropriate remedial action.

Gantt Charts
 

Gantt Charts are useful tools for analysing and planning more complex projects. They:

• Help you to plan out the tasks that need to be completed

• Give you a basis for scheduling when these tasks will be carried out

• Allow you to plan the allocation of resources needed to complete the project, and

Help you to work out the critical path for a project where you must complete it by a particular date. When a project is under way, Gantt Charts help you to monitor whether the project is on schedule. If it is not, it allows you to pinpoint the action necessary to put it back on schedule.

Sequential and parallel activities:
An essential concept behind project planning (and Critical Path Analysis) is that some activities are dependent on other activities being completed first. As a shallow example, it is not a good idea to start building a bridge before you have designed it!

These dependent activities need to be completed in a sequence, with each stage being more-or-less completed before the next activity can begin. We can call dependent activities 'sequential'.

Other activities are not dependent on completion of any other tasks. These may be done at any time before or after a particular stage is reached. These are nondependent or 'parallel' tasks.

Project Management

Why is Project Management important?

Project definition and proposal

10-Step guide to project planning

Project progress meetings

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