SAP S/4HANA migration is the biggest IT decision in the coming years for companies running ECC. SAP's mainstream maintenance for ECC 6.0 ends at the end of 2027, with optional paid extended maintenance until 2030. That timeline has turned "will we move?" into "how and when will we move?"
Three main approaches
Greenfield (new implementation)
S/4HANA is implemented from scratch, processes are redesigned around standard best practices, and only the required master data and open items are migrated. It is the cleanest way to shed years of custom code and complexity, but also the longest and most demanding, with the heaviest business involvement.
Brownfield (system conversion)
The existing ECC system is technically converted to S/4HANA together with its data and custom developments. History is preserved and business downtime is relatively short. On the other hand, old process designs and unnecessary custom code move along too, so post-conversion improvement must be planned separately.
Selective data transition
The middle path: only selected company codes, periods or processes are moved to a new S/4HANA system. It suits cases where several systems are consolidated or some units are redesigned, and usually requires specialist tools and an experienced team.
Which one to choose?
- If your processes have drifted far from standard and custom code is heavy: greenfield is a strong candidate.
- If your processes are healthy, history is critical and the timeline is tight: brownfield.
- If there are mergers, divestitures or a multi-system landscape: selective transition.
This is a business strategy decision, not a technical one. Having an independent ERP consultant compare the options on cost, risk and business value pays off most at this stage.
Preparation steps
- Readiness check: analyse which parts of the system are incompatible with S/4HANA and which functions are affected.
- Simplification list: assess functions that change or disappear in S/4HANA (for example Business Partner and credit management) and their impact.
- Custom code analysis: remove unused custom code and adapt the rest to the new data model.
- Data cleansing: start cleaning master data and open items months before migration; see the data migration guide.
- Archiving: archive old data that is no longer needed to shorten conversion time and reduce hardware needs.
Common mistakes
- Treating the migration as a purely technical upgrade and involving the business last
- Migrating custom code without measuring how much of it is actually used
- Not allowing enough time for testing and user training
- Leaving the cutover plan to the last month
An S/4HANA migration is a rare chance to review years of accumulated complexity. With the right approach you move not just to a new system but to simpler, measurable processes.
