I am preparing a business case for a new Project.

We have been debating the implementation model and the differences between a big-bang implementation, and one that is phased either but business unit, function or geographic location.

From my research, the big bang is generally quicker, cheaper but higher risk that a phased implementation. I understand the reasons and are happy with those but I haven't been able to find anywhere where they discuss just how much quicker the big-bang is compared to the phased roll-out, not even a rule a thumb.

Does anyone know of a rule of thumb or have some experience with this?

Thanks, Brett

  • 1
    I doubt there will be any rules of thumb and I have certainly never come across any- differences between the approaches will differ so widely and are so heavily dependent on context that any "model", no matter how high, is likely to be impossible in my view. The only thing you can sensibly do is two plans with a different risk profile for each and then look at cost/benefit of each relative to each other and the business appetite.
    – Marv Mills
    Jul 30 '14 at 11:40
  • Thanks Marv. I'm coming to the realization I will need to do both plans, I have been reluctant to do them to any great detail as we are still early in the process , I'm in a Government organisation, we have done a Market Scan but cannot go to RFP stage until funding is approved, so I'm working very much on incomplete data.
    – brettc4
    Jul 31 '14 at 7:36

In my experience it's a horses for courses type of a situation . In case of some projects the Big Bang approach works brilliantly while in some other projects I would settle for the Phased Implementation approach .

A number of factors have to be considered before deciding which approach serves best .

A few of these factors are :

Does the implementation cover a single site or multiple sites?

Does the implementation cover a single business or multiple businesses?

If a phased approach is adopted, what will this mean for integration between the new system and legacy systems during the interim period?

Are there any other competing business activities that need to be taken into account?

What level of risk is acceptable?

Which costs more – big bang or phased?


Some of the Pros & Cons of these two approaches are :

Pros of BIG BANG approach

No one has to operate their business in two different computer systems

· Everyone in the company moves forward on the same day.

· Cuts out the ability for people to say, “oh we’ll fix that issue until we convert fully”

· Shorter implementation time

· Pain and frustrations are condensed into one time period, not drawn out

· Lower costs

· Training needed only on the new system, not a changeover

Cons of BIG BANG approach

High risk

· A number of things can go wrong

· More pronounced problems

· Small details or issues can be overlooked in the rush

· Sink or swim for employees when it comes to learning the new system

· Testing can be tough prior to the implementation

· Failures in one part of the system can cause problems and failures in others

· Fall back plans do not always work out

· Performance can temporarily decline after the initial implementation as a result of employees adjusting to the new system


Less risk

· Employees learn as they go, there is no dip in performance after

· More time for users to adapt to the new system

· Not a sink or swim environment

· Small details and issues can be fixed as you go

· Skills and experience are gained with each step/phase which can help smooth the process as you get further along


Takes longer to be fully converted

· Not as focused as the big bang

· A state of continuous change can sometimes be disruptive

· Can have missing information because each module relies on info from others, so in a transitional period there may be some gaps

· Temporary bridges need to be made from old to new


Depending on the project one may even choose the Parallel Adoption approach . The Pros & Cons of this approach are :


· Least risky

· Users learn the new system while working on the old

· Slower pace than the big bang but faster than a phased roll-out


· Most expensive

· Employees have to enter data in both systems- this can be inefficient and breed data-entry problems

You may also choose to use a Combination of the above mentioned 3 approaches .

  • Thanks D_S for the info. I had found 1 of those links during my research, I am still naively hoping for a generally rule of thumb about the impact on costs thought :).
    – brettc4
    Aug 1 '14 at 2:33
  • Hi brettc4 , on most occasions Operating Expenses are lower if you adopt the Big Bang method because the organization need only incur the maintenance costs of a single system. The ROI is also faster because changeover occurs site-wide for all users on a given date . The risk pertaining to the Big Bang Method is related to unrealistic expectations that causes the staff to focus more on the deadline than the Planning process.The best way to determine which strategy is best for your organization is to assess factors such as initial costs, operating expenses, ROI, and impact on productivity.
    – DSarkar
    Aug 1 '14 at 10:56

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