Three Tools to Estimate Activity Duration

Estimate activity duration is an important project management process that helps you develop the project schedule. The accuracy of it depends on this process.

You use four tools to find the duration of your project or activities. The accuracy depends on when you do the estimation and the availability of the information.

As a project manager, you will use these techniques to provide duration estimates to your superiors. Understanding these terms is necessary.

Each activity has three attributes: resources required, the effort required and duration.

These attributes depend on each other. The more resources, the faster an activity can be completed. Moreover, an expert team member will take less time to complete a task than a novice team member. Therefore, first, apply the resources and effort. Then you will calculate the activity duration.

Estimate Activity Duration Tools

The following are four tools to estimate activity duration:

  • Analogous Estimating
  • Parametric Estimating
  • Three Points Estimating
  • Bottom-up Estimating

Analogous Estimating

You can use this technique on a project level or an activity level for a quick result.

Analogous estimates use analogies from past similar projects. For example, assume you have to estimate the duration of a project, so you will look into your organizational process assets (OPA) for a similar completed project. You will then pick the project that resembles yours the most. Using your expert judgment, you will choose the duration estimate for your current project.

This technique is useful when you have little information about your project, and management needs quick answers. The accuracy of this estimation depends on the similarities between your project and the project you are comparing it to.

This technique is also known as “Top-down Estimation.”

Key Points:

  • It is the fastest technique.
  • This technique does not provide an accurate estimation.
  • You can use this with a few project details.

Parametric Estimating

This technique uses historical records to compute the duration estimate. Parametric estimation seems similar to analogous estimation but it has a very different approach.

This uses statistical, historical data to find the estimate. For example, if constructing a ten-foot wall took one day, then how long will it take to build a hundred-foot wall? Multiply the time taken to build a ten-foot wall by ten.

Or, if one room took three days to paint in an earlier project. How much time it will take to paint twenty rooms on your current project? You will multiply the time taken to paint one room on the old project by twenty to get the duration for your new project.

This technique is more accurate than the analogous estimation.

Key Points:

  • It uses statistical relationships between historical data and variables.
  • It is more accurate than the analogous technique.

Three Points Estimates

You can reduce bias using three-point estimates.

Triangular and beta distribution formulas are the most popular three-point estimates.

In three-point estimates, we use three parameters:

  • Most Likely (Tm): This is the activity duration for most cases.
  • Optimistic (To): This is the activity duration in the most favorable case.
  • Pessimistic (Tp): This is the activity duration in the worst-case scenario.

The triangular estimate formula is:

Te = (To + Tm + Tp) / 3

PERT (Program Evaluation and Review Technique) is the most widely used three-point estimate technique.

It is a weighted average. The PERT estimate formula is:

Te = (To + 4Tm + Tp) / 6

Using a three-point estimate reduces the chance of risks, biased judgment, and uncertainty.

Key Points:

  • It uses three estimates to calculate the average value of an activity’s duration.
  • It reduces bias, risks, and uncertainties from the duration calculation.
  • It is more accurate than analogous and parametric estimation.

Bottom-up Estimating

Here, you will calculate the activities’ duration with the highest level of precision and add them together to get your project duration.

This is the most accurate, most time-consuming, and the most costly technique. It is also known as a “definitive estimate.”

Key Points:

  • This is the most accurate technique and provides reliable results.
  • You can use this technique when you have many details.
  • This is a costly and time-consuming technique.

Summary

Knowing accurate activity durations helps you create a realistic schedule and helps you complete the project with minimal obstruction. Activity duration is an iterative process. You can repeat this process throughout the project life cycle as needed. It helps you establish the schedule baseline of the project.

This is an important process for your project’s success. Any deviation from the schedule baseline can affect your cost baseline. This is bad for your project and can damage the credibility of your organization.

This is an important topic from a PMP exam point of view. You will a few questions from this topic in your PMP exam.

PMP Question Bank

This is the most popular Question Bank for the PMP Exam. To date, this PMP Question Bank has helped over 10,000 PMP aspirants pass the PMP exam. 

__CONFIG_colors_palette__{"active_palette":0,"config":{"colors":{"62516":{"name":"Main Accent","parent":-1}},"gradients":[]},"palettes":[{"name":"Default Palette","value":{"colors":{"62516":{"val":"rgb(59, 60, 61)"}},"gradients":[]}}]}__CONFIG_colors_palette__
More Details

PMP Formula Guide

This is the most popular Formula Guide for the PMP Exam. If you face difficulty with attempting mathematical questions for the PMP exam.

__CONFIG_colors_palette__{"active_palette":0,"config":{"colors":{"62516":{"name":"Main Accent","parent":-1}},"gradients":[]},"palettes":[{"name":"Default Palette","value":{"colors":{"62516":{"val":"rgb(59, 60, 61)"}},"gradients":[]}}]}__CONFIG_colors_palette__
More Details


Recommended Reading


Speak Your Mind

  • If you come to a problem that looks like a PERT / 3 Point question; however, the quest asks which tool do you use, and neither PERT nor 3 Point are there is the answer more likely to be Analogous or Parametric?

  • Hi Fahad,

    PMBOK guide 5 edition also mentions Triangular distribution which also comes under three point distribution. E = (P + O + M) / 3.

    Can you discuss the difference between triangular and beta distribution and in which scenarios they would be used.

    Do the triangular distribution be used where there is equal chance of best, worst and most likely estimates
    Whereas beta distribution would be considered where the chances of most likely estimates are more likely than the other two.

    I don’t get the difference between triangular and beta distribution not in terms of formulas but in which cases they are used and how they are different to each other.

    Thanks
    Sushil

  • please can you help solve this question…….Tiles (6”X6”) can be installed at the rate of 55 tiles per worker hour. The floor of a large lobby area (80’X50’) is to be covered with these tiles. If three workers are assigned to this task, what duration should be assigned to this activity?

    • Tile size = 6″ x 6″ = 36 SQ.INCH
      Tile size = 0.5′ x 0.5′ = 0.25 SQ.FT.
      Productivity of 1 worker per hour = 0.25 x 55 = 13.75 SQ.FT.
      Productivity of 3 workers per hour = 0.25 x 55 x 3 = 41.25 SQ.FT.
      Total lobby area = 80′ x 50′ = 4000 SQ.FT.
      Now,
      Duration of Activity = Total lobby area / Prod. of 3 workers per hour
      Duration of Activity = 4000 / 41.25 = 96.96 hours
      If, you devide total no of hours by 8 (hours / day), you can find duration of activity in no. of days = 96.96 / 8 = 12.12 days

  • Hello Fahad,
    There is an additional doubt about estimate durations. I thought that parametric estimating method was defined for the relationship between certain kind of data as, effort – productivity and calendar.

    Your post has made me to realize about something, based on the following considerations: If an estimate is not a precise figure but it is a range of time or cost… a parametric estimate based on effort – productivity and calendar is quite precise to be an estimate. then, using those parameters I couldn´t estimate but determine activity duration.

    could please clarify this confusion that I have?

    • In parametric estimation technique, the estimation is dependent on the data you are using from your past experience. Therefore, you must analyse data for its quality before using it in the parametric estimation technique.

  • Thanks for contribution such helpful information. The information provided is very nice and this information is not available so easily. Therefore I thank the writer for the useful input.

  • {"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}

    Recommended Resources

    Use these resources for your PMP certification exam preparation and pass the exam with minimal effort.

    __CONFIG_group_edit__{"jv80vv8f":{"name":"All Image(s)","singular":"-- Image %s"},"jv812jsg":{"name":"All Title(s)","singular":"-- Text %s"},"jv812qp8":{"name":"All Name(s)","singular":"-- Text %s"},"jv812zdt":{"name":"All Divider(s)","singular":"-- Divider %s"},"jv813402":{"name":"All Paragraph(s)","singular":"-- Text %s"},"jv813af5":{"name":"All Button(s)","singular":"-- Button %s"},"jv813f5t":{"name":"All Content Box(s)","singular":"-- Content Box %s"},"jv813k1c":{"name":"All Column(s)","singular":"-- Column %s"}}__CONFIG_group_edit__
    __CONFIG_local_colors__{"colors":{"c85e2":"Button ","f242c":"Border"},"gradients":{}}__CONFIG_local_colors__

    The PMP Training Program


    The PMI approved 35 contact hours training program that is 100% online, affordable, and help you prepare the PMP exam.

    __CONFIG_colors_palette__{"active_palette":0,"config":{"colors":{"3e1f8":{"name":"Main Accent","parent":-1}},"gradients":[]},"palettes":[{"name":"Default Palette","value":{"colors":{"3e1f8":{"val":"rgb(255, 255, 255)","hsl":{"h":210,"s":0.01,"l":0.99}}},"gradients":[]},"original":{"colors":{"3e1f8":{"val":"rgb(19, 114, 211)","hsl":{"h":210,"s":0.83,"l":0.45}}},"gradients":[]}}]}__CONFIG_colors_palette__
    Read More

    The PMP Exam Preparation Tool


    A PMP exam preparation course, that is 100% online and provide you everything you need to pass the PMP exam.

    __CONFIG_colors_palette__{"active_palette":0,"config":{"colors":{"3e1f8":{"name":"Main Accent","parent":-1}},"gradients":[]},"palettes":[{"name":"Default Palette","value":{"colors":{"3e1f8":{"val":"rgb(255, 255, 255)","hsl":{"h":210,"s":0.01,"l":0.99}}},"gradients":[]},"original":{"colors":{"3e1f8":{"val":"rgb(19, 114, 211)","hsl":{"h":210,"s":0.83,"l":0.45}}},"gradients":[]}}]}__CONFIG_colors_palette__
    Read More
    >