Project planning requires good project estimating to produce an achievable project schedule and a greater chance of on-time delivery. An essential skill to good project management is accurate time estimation.

There are two key reasons why it is of utmost importance to get time estimates correct:
- Time estimates drive the setting of deadlines for project delivery, and therefore the project and its management's reliability
- Correct estimations will often determine the pricing of contracts and therefore their profitability

Avoid underestimation

More often than not it occurs that project managers vastly underestimate the time required to implement a project and its different components. What seems to happen on a regular basis is that unplanned or unexpected events are not taken into account and no provision is made for unscheduled high-priority work.

Project planning often does not identify all of the tasks that need estimating and, as all project managers are aware, each project is different in terms of objectives, scope, resources, constraints and risks. What occurs all too often is that project estimating tends to suffer from over-optimism, with estimators not allowing enough time to either do the work or solve the inevitable problems that emerge.

Project managers often simply fail to allow for the full complexity involved with a project. Therefore, time allowances need to be made for unexpected occurrences. Project time estimates are one of the central points of producing an effective project schedule, and managers need to understand project time estimation and ensure good project estimates are produced, thereby increasing the chances of a successful project.

Detailed task lists

The first stage in estimating time correctly is to review 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.

Prepare a detailed list of all the tasks that must be achieved and make your best guess at how long each task will take to be completed. You can base your estimate on past experience to begin with. Within this basic estimate you must allow time for detailed project planning, meetings, liaison with external parties, quality assurance and any paper work completion that needs be done.

Also ensure time allocation for unpredictable events, which could add significant time onto your project, such as:
- Accidents and emergencies
- Holidays and sickness of essential staff
- Equipment breakdowns and malfunctions
- Missed deliveries by suppliers
- Quality control rejections

Once the first draft of tasks and estimated completion times has been formulated, you can be more specific on time allocation by using PERT (Program Evaluation and Review Technique) for critical tasks, if not all tasks. It is important to note that most projects take longer than expected due, primarily, to the over-optimism, a good human quality but not when it comes to time estimates, of both the project manager and anyone, expert or otherwise, assisting with producing the estimates.

PERT, which will have been taught to project managers, will compensate for the over-optimism on the part of the project manager, and allow for a more accurate time estimate to be produced. Microsoft Project is the first choice of most Project Managers for their software solution, and Microsoft Project Software training the key to success with it.