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See more than the tip of the iceberg – how the 30 per cent rule helps project planning

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Trying to predict the outcome of a project a couple of months down the line during the initial planning phase can sometimes feel like trying to predict the weather on a specific day in the next season, in a different country.

While you can predict approximately how the weather will feel in, let’s say, summer or winter, you cannot really say with a significant level of accuracy what the weather will be like on a given day, and yet this is what we expect from a project plan.

When we are trying to plan for the next project, there are usually many unknowns and multiple variables, making it almost impossible to predict exactly the outcome of a project at its end. This variance is amplified to an extent when we talk about projects that will last for years.

A helpful rule of thumb

What I have found useful is the rule of +/-30 per cent. For example, whatever you accounted for in terms of cost, assume +30 per cent (as costs tend to overrun). And whatever you planned for the timeline, add another 30 per cent of work time to be on the safe side.

The same is true for quality – although things there can be trickier to quantify – but it helps to consider a baseline up front in order to adjust your plan accordingly. So, if you are estimating to get around 100 issues over the course of a complicated project, ensure your plan can account for 130 at a minimum.

There is not a one-size-fits-all solution for creating project plans, as there is no such thing as a standard project. Projects are required for any industry and every profession, and even in your personal life, such as planning your wedding (well, you can’t really add 30 per cent to your timeline on this one).

One other factor that can vary from project to project is the people who are part of the team. People can be critical to project success – to find the right people and stick with them throughout increases the chances of staying as close as possible to initial project predictions.

Ambiguity and diversity

I have found that experience and diversity are the two key factors when aligning the right people to the right project. Being able to bring people with different backgrounds into a room to work towards a common goal always adds value to a project. This is especially true when working on a project that has a high level of ambiguity.

Diversity means that people with a wide range of experiences and expertise are coming together, and ultimately these combined perspectives will consider outcomes and solutions that may not have been addressed otherwise. This is an opinion I always try to share with my colleagues and one I highlight when I am exploring new opportunities: bring people with different backgrounds onto projects. Do not only look for people who were doing exactly the same thing before and will do the same thing after.

Of course, it can be important for the project lead to have related experience, but we should also be open to giving people a chance to learn and grow and perhaps add their own differing perspectives to the mix. I have found that it is when challenged that most people find a way to excel.

So, what is this blog about then? Is it about the +/-30 per cent rule or the people who will bring more chances for success? Well, it is about both – but there are many more success factors. These are the two fundamentals that you should consider when you are still in the planning phase of a project.

There is no guaranteed way to predict with accuracy – that’s why it always feel like we are only seeing the tip of the iceberg when we are planning for a project, compared to when we are executing, it mostly feels that we see the entire iceberg.

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  1. Matt Whyndham
    Matt Whyndham 10 March 2022, 03:00 PM

    Interesting topic! I've always advocated building in a series of margins like this, although I've never been brave enough to quote a number. When asked, I usually sidestep and say "it depends". Perhaps this heuristic could be usefully combined with Eddie Obeng's typology of projects. For Painting By Numbers type projects: allow 10-20% on any estimate. Quest and Making Movies : 30%, as decsribed here. Lost in the Fog : 100% or more?