An ERP migration plan in six stages
The projects that fail tend to move everything at once and redesign nothing. A plan that moves one process at a time, with the old system still running, removes most of the ways an ERP migration goes wrong.
Contents
An ERP migration fails slowly and then in public. Gartner’s senior director of ERP strategy says 70% of ERP initiatives fail to fully meet their original business case and 25% fail catastrophically1. The plan below is built from what the failure studies say went wrong.
What the evidence says goes wrong
Three findings recur. The first is that companies move the old process unchanged: 49% of the SAP migrations in ISG’s survey carried out little or no re-engineering, and fewer than one in five organisations reimplemented processes and technology together2. The second is that the difficulty is human. ISG’s principal analyst told The Register that "a lot of the delays are caused by people, not necessarily the technology"2, and ASUG’s member research names business process change as the largest barrier, at 49%, ahead of customisations at 44% and organisational inertia at 37%3.
The third is duration. Lidl’s merchandise-system project ran for about seven years before it was stopped, and the company’s own memo said the goals could not be reached at acceptable expense45. A plan that cannot show a working result in its first months has no way of finding that out early.
Choosing the strategy
| Strategy | What moves | Share in ISG’s survey2 |
|---|---|---|
| Brownfield | The existing system is converted, with its configuration and custom code | 34% |
| Greenfield | Processes are designed again on a new system | 18% |
| Mixed | Selected parts are converted, others rebuilt | Nearly half |
| Staged, process by process | One process at a time moves to the new system, which reads from the old one until the ledger moves | Not measured |
The staged strategy was impractical when the new system was another monolithic suite. It becomes practical when the target is a set of modules on a data layer the company owns, because each module can go live against data still mastered in the old ERP.
The six stages
1. Inventory. List the modules in use, the custom code, the interfaces and the reports people open every week. Mark which of them carry a real process and which are habit. More than half of ISG’s respondents agreed they had over-customised their old ERP2; the inventory is where that is found.
2. Redesign. For each process worth keeping, write how it should run, with the people who run it. This is the stage most projects skip. OpenLazarus’ own guidance makes the same point from the AI side: improve the underlying process before automating it, and clean and organise the data before connecting AI to it.
3. Data. Decide which system masters customers, suppliers, items and prices during the transition, and fix duplicates and gaps at the source. Agree what history must move and what can stay readable in an archive.
4. One process, end to end. Choose a process with volume and a clear measure, such as order entry from email or purchase-order follow-up. Run it on the new system against the old ERP’s data, with a named owner, approval rules for anything an AI agent does, and a number agreed in advance.
5. Widen, in parallel. Add processes one at a time. For each, run old and new side by side for a set period and reconcile the results before switching the old one off. Keep the old system supported throughout, under extended maintenance or third-party support67.
6. The ledger, last. Move finance when the operational processes that feed it are stable. Close a period in both systems, reconcile, and only then retire the old one.
A checklist for the steering group
Before each stage begins
- A named owner for the process, from the business and not from IT.
- A written description of how the process will run after the move.
- A measure and a target, agreed before go-live.
- Data rules: which system is the master, and until when.
- Approval rules for automated actions, set per action.
- A support contract for the old system that outlasts the plan by a year.
- A stop rule: what result would pause the programme.
What success looks like
After the first stage the company has one process running better than before and a measured result to show for it. After the last, it has one system, one set of data and no cut-over weekend to remember. The cost lines for each stage are in the cost guide, and the question of what to do with the old system’s AI gap in the meantime is covered in legacy ERP modernization with AI.
Questions buyers ask
What are the steps in an ERP migration?
Six stages. Take an inventory of what the old system does, redesign the processes worth keeping, clean and map the data, move one process end to end, run old and new in parallel for the processes that follow, and move the ledger last. Each stage ends with a measured result before the next begins.
What is an ERP migration strategy?
The choice of how much to change and in what order. In ISG’s research on SAP migrations, 34% of companies chose a brownfield conversion of the existing system, 18% a greenfield reimplementation and nearly half a mix. A staged, process-by-process migration is a fourth strategy that becomes possible when the new system can read from the old one.
Why do ERP migrations fail?
Mostly for reasons of people and process. ISG’s principal analyst said that "a lot of the delays are caused by people, not necessarily the technology", and its survey found 49% of projects doing little or no re-engineering. Gartner’s ERP strategy lead puts the share of initiatives that fail catastrophically at 25%.
What should an ERP migration checklist include?
An inventory of modules, custom code, interfaces and reports. A named owner per process. Data rules for customers, suppliers, items and open transactions. A success measure for the first process. A parallel-run period with a reconciliation routine. A support arrangement for the old system that lasts until the final cut-over.
Sources
- ERP carnage continues as orgs jump in unprepared. The Register, 13 Nov 2025. Accessed 11 Nov 2026.
- Most SAP migrations bust budgets and deadlines, study finds. The Register, 5 Feb 2026. Accessed 11 Nov 2026.
- Two-fifths of SAP Americas users yet to ditch legacy ERP. The Register, 5 Nov 2025. Accessed 11 Nov 2026.
- Lidl stoppt millionenschweres SAP-Projekt für Warenwirtschaft. Computerwoche, 18 Jul 2018. Accessed 11 Nov 2026.
- Lidl cancels SAP introduction having sunk €500 million into it. Consultancy.uk, 13 Aug 2018. Accessed 11 Nov 2026.
- SAP S/4HANA: commitment to innovation and maintenance until 2040. SAP News Center, 4 Feb 2020. Accessed 11 Nov 2026.
- Third-party support for SAP. Rimini Street. Accessed 11 Nov 2026.
Updated 11 Nov 2026: First published.