16 May, 2024

How to Estimate Your Project Schedule

Arriving at a robust project schedule is hard. But, in this video, I will break it down into a simple process with three phases and 10 steps

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The Project Schedule Estimation Process

I have divided my consolidated project schedule estimation process into three phases:

  1. Understanding
  2. Estimating
  3. Protecting

Let’s look at each stage, and further divide the process into a total of ten steps for estimating your project Schedule

Phase 1: Understanding

  1. Understand the context of your project
    This will give you an idea of political pressures and external dependencies.
  2. Understand history
    Look for reference projects and parametric data you can use. This can be one of the most robust approaches to estimating, if the projects are truly comparable. So, also aim to understand what systematic differences there are.
  3. Understand the requirements 
    Do your research on what the stakeholders need. And also, look at how differing requirements among stakeholders can lead to conflict and future political pressures that can affect costs and schedules.
  4. Document your assumptions
    All estimates and forecasts are rooted in a set of assumptions. There’s nothing wrong with that. But what can be a problem is untested assumptions. More so still, embedded assumptions that you aren’t fully aware of. So:
    • Articulate and document all of your assumptions
    • Test each of them for validity or at least plausibility
    • In the latter case, check the impact of applying a different assumption
    • Change them if you need to

Phase 2: Estimating

  1. Initial, Top-level estimate
    Start with a high-level initial estimate.
    OOM, top-down, parametric, or experience-based (expert judgment). Agile estimating techniques work well here to: Story pointing, bucket or Tee-shirt sizes, or planning Poker
  2. Detailed estimate
    The most structured approach is to break your project down into parts with a WBS and use bottom-up planning. This is where you might start to use 3-point estimates or even use the Monte Carlo method.
  3. Confidence level
    Add confidence levels to your estimates, to get a sense of how certain or not you are.
    An estimate only has value when we also express with it the level of confidence we have. Confidence is the inverse of uncertainty. Experience, data, rigor, checking, and review all decrease levels of uncertainty and increase our confidence levels. Novelty, volatility, ambiguity, and complex stakeholder environments decrease our confidence in any estimates we make. We often express uncertainty or confidence in a range:
    • Time estimate: 12 days +/- 2 days. This is an example of a symmetric confidence range
    • Schedule estimate: 30 September +20 days / – 10 days. Note this is an example of an asymmetric confidence range

This will inform…

Phase 3: Protecting

  1. Contingency
    Add extra time to your estimates, based on how confident you are about your estimates. For example:
    • How familiar or novel is what you are doing?
    • What is the level of risk?
    • How complex is the task?
  2. What if?
    Analyze different scenarios, and see how your estimates and contingency will fare. Select a range of plausible scenarios – including some your team may consider to have a low likelihood.
  3. Checking and review 
    Always check your arithmetic. And compare your estimates with a simple Back of the Envelope estimate as a simple sense-check. You may want to carry out a Red-team review.
    At the completion of your estimating process, hand over all your calculations and assumptions to the smartest, most critical people you can find. Invite them to test and challenge everything. The more holes they find in your calculations, assumptions, and methods now, the better. It’s only later that you will have lost the chance to fix them.

Carefully curated video recommendations for you:

What Kit does a Project Manager Need?

I asked Project Managers in a couple of forums what material things you need to have, to do your job as a Project Manager. They responded magnificently. I compiled their answers into a Kit list. I added my own. 

Check out the Kit a Project Manager needs

Note that the links are affiliated.

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Mike Clayton

About the Author...

Dr Mike Clayton is one of the most successful and in-demand project management trainers in the UK. He is author of 14 best-selling books, including four about project management. He is also a prolific blogger and contributor to ProjectManager.com and Project, the journal of the Association for Project Management. Between 1990 and 2002, Mike was a successful project manager, leading large project teams and delivering complex projects. In 2016, Mike launched OnlinePMCourses.
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