Bottom-up estimating is an approach that entails estimations on a granular level for parts of a job. These are then aggregated to a total estimate for the entire task. It is frequently referred to as among the most specific ways of estimating. Estimating expense, duration or reresource needs of a task generally starts with a rough order of magnitude in the beginning. This is complied with by even more exact approximates later in a job.

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In this article, we will present theidea, cover the distinctions and interdependencies through other estimationmethods and administer guidance to and an instance of bottom-up estimating injobs.


What Is Bottom-Up Estimating?

Example of the aggregation of bottom-up approximates (click to enlarge).
The requirements monitoring team, forinstance, might have offered analogous estimating. In that case, they estimatedtheir resource, time and budobtain needs based on observed worths from previousworkshops and also specifications. Thus, they came up with approximates of 12 persons,29 days and also $104,400 for their workstream.

The testing team, on the various other hand also, mightknow just how many test cases a perkid usually creates per day and how many instances ateam member commonly completes per day. They multiply these parameters through thevariety of expected test cases in the present project, i. e. they are applyingthe parametric estimating approach.

The light-blue rows in the over table showthe estimates on the job-related package level (i.e. the sum of the approximates of theactivities). The dark-blue lines recurrent the second level of aggregation – theamount of sources, prices and also duration on a phase level (equivalent level to thatof deliverables in various other WBS types).

The oselection cells contain the totalaggregates for the entirety project: a full headcount of 47, a sum of time neededof 274 days (which is not necessarily the project duration, see explanationbelow) and total price of $893,700.

Note that the numbers of headcount and also timeare just the sums of the corresponding granular approximates. In truth, theheadcount might be lower as some team members might work in differentactivities and also work-related packperiods. For circumstances, a business analyst who writesspecifications could also be deployed for testing in a later on task phase.

The sum of the duration estimates of all activities does not necessarily equal the complete duration of the job. This is because scheduling may lead to parallel tasks or waiting time that is not estimated on the task level. This is actually a part of the advance of the in its entirety schedule.

Advantages and Disadvantages of Bottom-Up Estimating


Bottom-up approximates have the right to be veryaccurate. This is bereason team members are estimating the item of job-related theyare responsible for. As they commonly have the the majority of expertise of their workpackage, their approximates tfinish to be much even more accurate than top-down estimates.Estimation errors can balanceout across the components of a job. If the time or cost of one occupational packagehas actually been underapproximated, for instance, this could be counter by anoverestimation of another job-related package. Such errors might therefore notnecessarily impact the budobtain baseline at the task level.Bottom-up estimating deserve to beoffered in conjunction with other estimation methods, e.g. the task durationmight be obtained with parametric or analogous estimating.


The underlying assumption isthat the job estimate is composed of the sum of its pieces. This may ignoreoverhead and integration initiatives that might take place in enhancement to the occupational definedin activities. This holds for big and complicated jobs, in specific.The bottom-up estimation itselfcalls for a lot even more resources than various other approaches such as analogous estimating(top-down estimation).The expense estimation is based onthe duration estimate. Both rely on the approximated reresource demands. Hence,an estimation error tbelow would certainly lead to inspecific time and also price estimates aswell.In practice, bottom-up estimateshave the right to be at risk to the prejudice or the interests of the estimators. While this appliesto all types of approximates (to some extent), it might be less controllable inbottom-up estimating. This is bereason these estimations are typically done by manyvarious estimators, i.e. those responsible for a occupational package.


Bottom-up estimating can be a very accuratemethod to recognize the definitive estimate of a task. It requires a certainamount of resources and also an established occupational breakdown framework. The projectshould have been damaged dvery own to the work-related package and activities level prior to youhave the right to apply this technique.

Apart from estimating resources, time andcosts for the planned work of a project, this strategy can also be offered toassess adjust repursuits, e.g. in the course of a cost-benefitevaluation of such transforms.

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There are likewise numerous various other techniques to estimate the costs or duration of projects and also their components. Make certain you review our article on expense estimating and also estimating activity durations to acquire a summary and comparichild of the different viewpoints.