Successful SAP S/4HANA implementation is decided long before go-live, by the choices made during SAP migration planning. These include the migration approach, deployment model, scope, data strategy and partner. Get them right and the move becomes a business transformation; get them wrong and it becomes an expensive technical upgrade.
The deadline is real. SAP ends mainstream maintenance for ECC 6.0 in December 2027, and extended maintenance at an additional cost runs until December 2030 (ERP Research). Large S/4HANA programs often take 18 to 36 months, so organizations that have not started planning are already short of time.
This article covers the key decisions to make, the risks to manage and the best practices that keep an S/4HANA migration on time and on budget.
Key decisions in SAP migration planning
1. Migration Approach
The first and biggest decision is how to get from ECC to S/4HANA. There are three main approaches:
| Approach | What It Means | Best For | Trade-offs |
|---|---|---|---|
| Greenfield (New Implementation) | Build a fresh S/4HANA system using standard processes, and migrate selected data. | Organizations wanting to redesign processes and remove technical debt. | Highest change effort; historical data needs a plan. |
| Brownfield (System Conversion) | Convert the existing ECC system, keeping its configuration, custom code and history. | Stable processes, heavy customization, tight timelines. | Carries old complexity forward; less process improvement. |
| Selective Data Transition (Bluefield) | A new S/4HANA system shell into which selected processes, org units or history are moved. | Complex landscapes, mergers and divestments, or mixed goals. | Needs specialist tools and partners; more complex to plan. |
2. Deployment Model
Decide whether S/4HANA will run on-premise, in a private cloud through RISE with SAP, or as S/4HANA Cloud Public Edition. Public cloud favours standard processes and continuous updates. Private cloud and on-premise allow more flexibility and customization.
3. Scope and Sequencing
Choose between a big-bang go-live and a phased rollout by company code, region or business unit. Phased rollouts reduce risk but extend the period of running two systems in parallel.
4. Custom Code
Decide which custom code to retire, replace with standard functions or rebuild using clean-core principles, such as side-by-side extensions on SAP BTP. Usage analysis often shows that much custom code is never used.
5. Data Strategy
Decide how much history to migrate, how to cleanse and harmonise master data, and what to archive. Business partner conversion, which merges customers and vendors, needs particular care.
6. Integration and the Surrounding Landscape
Map every interface, third-party system and reporting tool, and decide how each will connect to S/4HANA.
SAP migration planning, step by step
Most programs follow a structure similar to SAP Activate, which runs through the Discover, Prepare, Explore, Realize, Deploy and Run phases. The planning work happens in the first three:
- Assess readiness. Run SAP's Readiness Check, analyse custom code and usage, and review add-ons and data quality.
- Build the business case. Link the migration to business outcomes, such as faster close, real-time reporting, process automation and AI, not just to the end of support.
- Make the key decisions. Settle the approach, deployment model, scope, sequencing and data strategy, as described above.
- Design the target landscape. Define the future processes, integrations, extensions and reporting architecture.
- Plan the program. Set the roadmap, budget, governance, team structure and partner model.
- Prepare the organization. Start change management, communications and training planning early.
- Plan testing and cutover. Define test cycles, rehearse the data migration through mock loads, and plan cutover and hypercare.
Major risks and how to mitigate them
| Risk | What Goes Wrong | How to Mitigate It |
|---|---|---|
| Unclear Business Case | The program becomes a technical upgrade with little value. | Tie scope to measurable business outcomes, with executive ownership. |
| Poor Data Quality | Load failures, duplicates and incorrect financials at go-live. | Start data cleansing early; run several mock migrations. |
| Custom Code Overload | Effort and cost overruns; harder future upgrades. | Retire unused code, adopt standard processes, follow clean-core principles. |
| Underestimated Testing | Defects reach production. | Use automated regression testing and involve business users in user acceptance testing. |
| Integration Gaps | Interfaces break at cutover. | Build a full interface inventory, then test end to end. |
| Skills Shortage | Delays from a lack of S/4HANA expertise. | Secure partners and augment the team early; train internal staff. |
| Weak Change Management | Low adoption and productivity dips. | Engage the business from day one; use role-based training and change champions. |
| Unrealistic Timeline | Rushed design and a risky go-live. | Plan backwards from a realistic date with buffers, and phase where needed. |
Best practices for SAP S/4HANA implementation
- Start early. With the 2027 deadline approaching, partner capacity and skilled consultants will get scarcer and more expensive.
- Lead with the business. Make process owners accountable for design decisions, not just IT.
- Adopt a clean core. Keep the core as standard as possible, and build extensions outside it so upgrades stay simple.
- Fit to standard. Challenge every request for customization, and use SAP best-practice processes as the starting point.
- Treat data as a workstream of its own, with dedicated owners, quality metrics and repeated mock loads.
- Automate testing for regression, integration and performance, so you can test often.
- Invest in change management with clear communication, role-based training and post-go-live support.
- Choose the right partners, looking for proven S/4HANA experience in your industry and a clear method.
- Plan hypercare and continuous improvement, because go-live is the start of optimization, not the end of the program.
Conclusion
Strong SAP migration planning turns a deadline-driven upgrade into a real business transformation. Settle the big decisions early: approach, deployment model, scope, custom code and data. Manage the main risks actively, and follow proven best practices.
With a clear business case, a clean core and the right team, your SAP S/4HANA implementation can deliver faster processes, better insight and a platform ready for future innovation.
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