If you never attend any project management training, you may do it based on your past experiences or follow steps of former in your organization. Maybe do the estimation in Excel worksheet and list down what tasks you will do in the project and estimate how long you will complete them. Then, aggregate figures and develop the schedule, then reported to your boss the start date and finish date. Any problem happen? Another method may be estimated roughly to have one figure e.g. about three months to complete the project through your expect judgment. But, do you think how accurate such estimation technique is? Do you think that it is one reason causing project failure due to behind schedule and over budget consequences?
Can we estimate time and cost be accurate and controllable? YES. Try to decompose the project in details as possible. Otherwise, you are no way to make it accurate. But, it’s also most time-consuming method for project estimating. Project Manager is responsible to decide when would the best time using this technique.
Bottom-up estimating is one way to estimate time and cost from detail level starting and then aggregated to most upper level to obtain a larger estimate for the entire task as a whole. How it is?
There are five steps to perform Bottom-up Estimating:
Step 1: Break down your project into activities
Step 2: Estimate activities
Step 3: Determine the dependencies among the activities
Step 4: Determine what resources required and when it’s available
Step 5: Aggregate your estimates into totals for each deliverable
Does step 1 – how to break down the project into pieces. According to PMBOK Guide it highly recommends the use of Work Breakdown Structure (WBS) as the best practice for identifying and managing work packages (Work Package will be further decomposed into activities, but the lowest level in WBS must be Work Package). For the use of WBS, we can find it easily in Internet and there are huge amount of resources about it.
Does step 2 – According to PMBOK Guide Project Manager actually should not be Technical guy or Expect to do the activities. The tasks should be handled by Expect in Project Team so who do it then who should perform the estimation of the activities. In real-world it may be not as the Project Manager/Coordinator may be required to complete the activities by himself/herself in small size project in some organization. Estimation and actually complete the works may be done by Project Manager himself/herself.
Does step 3 – There are 4 logical relationships between activities: start-to-start, start-to-finish, finish-to-start and finish-to-finish. For example, finish-to-start means predecessor activity must finish before successor activity can start. Also, dependencies are categorized into Mandatory, Discretionary and External. These relationships and dependencies will directly affect developing schedule as some activities can be done concurrently and some can’t.
Does step 4 – What resources are you selected to perform the project is also important factor to effect the accuracy of estimation. As skilled or expect team member can complete the works quickly then inexperience one. Also, when the resources are available is also important factor to effect the schedule.
Does step 5 – Aggregate all estimation of work package together, we can get total time required to complete the project and start date and end date to complete the schedule.