Pros and Cons of Big Bang vs Phased Rollout

February 16, 2021

By Brandon Long


The most important time in any HCM implementation is system go-live. One of the most essential questions about go-live should be answered well in advance: Do I go-live all at once, or in phases?

As with most questions in any software implementation, the answer is a solid “it depends,” but here is an overview of some pros and cons to consider when making the decision.


Big Bang Pros:

  • Resource intensive
  • When the project runs smoothly, a shorter implementation timeline
  • The project team can focus on one phase of the project at a time
  • Everyone at once allows better campaigning for more change management
  • Smaller cost of maintaining both systems for less time

Big Bang Cons:

  • Small issues are seen by everyone (end-users as well as project stakeholders and HR team), potentially undermining the success of adoption
  • Syncing data from the old system to the new system is a considerable undertaking, and a big bang approach leaves no overlap for parallel testing
  • One troublesome group of rules can delay the entire population
  • The entire project must be completed before ROI is realized
  • Project team focus must simultaneously focus on all populations throughout the project

Phased Rollout Pros:

  • Allows for earlier realization of ROI from initial populations
  • Ability to get something out the door even if certain groups set for deployment in a later phase have unforeseen delays or complications
  • Additional time for change management initiatives
  • Allows to target early adopters who may be more understanding of bugs
  • Overlap of system rollout allows more time for parallel testing

Phased Rollout Cons:

  • The additional cost of maintaining your old system for longer
  • It makes the resource-intensive go-live phase longer and repeated
  • Employees transferring out of the live group into the non-live group can have a rocky experience or even be unsupported
  • When the project runs smoothly, it causes an extended project timeline
  • Attention becomes diverted when one group is live, and other groups are still rolling out and in testing

In summary, most of the pros and cons come down to risk and cost.  Big Bang has the potential to be cheaper, but the simultaneous go-live has more significant exposure to risk.  The phased rollout has the potential to be costlier, but with much better risk mitigation potential.

Some additional considerations when choosing a rollout strategy include choosing the initial population.  One point for consideration is whether to go live with a small pilot group or go live with a large population all at once.  Small pilot groups work great for debugging initial go-live issues and system errors to help build confidence in the system once a larger rollout is planned.  When you do a small pilot group, you can easily run a full parallel test with the old system.  A larger go-live group of a whole initial population does allow you to see ROI on the initial population. Still, it opens you up to some of the risk of a big bang rollout.

No matter which initial go-live approach you choose – everyone, a population, or a pilot group – smaller populations means less risk but longer timelines.  Finding the right balance of any implementation can be a challenge.

If you’re preparing for an HCM system implementation, HRchitect is widely considered one of the best strategic technology consulting firms and is your best insurance policy for a successful implementation. Reach out to us today!


Brandon Long is an HCM Implementation Consultant and has over eight years of experience with workforce management systems, including consulting and training.  Brandon has extensive knowledge of product capability as well as experience configuring and navigating complex workforce management implementations spanning multiple industries. Brandon has technical expertise leading all phases of a project, from scope definition and requirements documentation, through configuration, testing, implementation, go-live support, and post-go-live support.


Learn more about Brandon here