Estimating Time Accurately
Accurate time estimation is a skill essential to good project management. It is important to get time estimates right for two main reasons:
- Time estimates drive the setting of deadlines for delivery of projects, and hence peoples' assessments of your reliability
- 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.
This section discusses how to estimate time on small projects. Time estimates are important inputs into the other techniques used to organize and structure medium and large sized projects (Gantt charts and Critical Path Analysis). Both of these techniques reduce large projects down into a set of small projects.
How to Use the Tool:
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. Simple techniques such as Drill-Down are useful for this.
Once you have a detailed list of all the tasks that you must achieve, 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.
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