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How long will a legacy migration take?

How long will a legacy migration take? This is a common question and it is important to have a process to follow to answer with truth, transparency and a detailed amount of due diligence. Too many legacy migration projects have failed because they have not addressed this question sufficiently.

To work out how long a legacy migration will take, there is a process you can follow that will give an estimation with a good level of certainty. Like all process, there is some input, a process to follow, and then some output. This might seem basic, but it is important to think in this context.

This article is purposefully matter of fact and there is more of an explanation behind the process in the links below and explained more in the summary.


  • UI of the legacy system (Sandbox Site)
  • Old documentation into the library (as much as possible)
  • Database schema from the Legacy database schema


The roots causes of legacy systems come from the loss of knowledge and control. To start rebuilding the knowledge and regaining momentum, record all your meetings!

  • Using the Library gather as much legacy documentation as possible. The articles are created using the Markdown Basics.
  • Create a behaviour identification spreadsheet from the External Resources
  • Reverse Engineering Requirements into a backlog (initially record in the behaviour identification spreadsheet)
  • Create a UX Flow (UI map, Menu flow, etc) from the UI of the legacy system
  • Mark the UX Flow with the requirement ID's from the backlog
  • Cross check all requirements are covered in the UI and vica versa (super duper important for due diligence)
  • Complete the behaviour identification spreadsheet
  • Create an entity requirements spreadsheet from the External Resources
  • Copy the tables name and backlog into the spreadsheet and identifiy what tables are needed for this milestone
  • Copy the backlog into the plan on the platform and organise into boards
  • Migrate the old schema (include only tables for this milestone) into the entity diagram
  • Create as many of the pages and tiles into the UI diagram
  • Fill out the secruity diagram and create any new entities with user behaviours as required
  • Create a time estimation spreadsheet from the external resources
  • Complete any tech spikes to firm up estimations
  • With at least 3 people, complete the estimations


  • Time Estimation Spreadsheet
  • Behaviour Identification Spreadsheet
  • Entity Requirements Spreadsheet
  • UX Flow
  • Plan with backlog
  • Entity diagram
  • UI diagram
  • Security diagram
  • Meeting Videos
  • Tech Spike (if required)


If you are interested in getting qualified to answer the question: how long will a legacy migration take; I recommend joining up to Codebots and completing the Estimating a Project qualification in the academy. Some of the lesson cover:

  • The Theory of Estimatin Software
  • Software Development Methodologies
  • Managing Risk
  • Estimation Allowances
  • Calculating the Estimation