SAP ECC to S/4HANA Migration: What You Need to Know Before 2027

Standard maintenance for SAP ECC 6.0 ends in 2027. For IT teams and industrial management who haven’t yet launched their migration project, the countdown has begun. An SAP S/4HANA project takes an average of 14 to 24 months. Start in 2025 and you’ll be on time. Wait until 2026 and you’re taking a serious risk.

This guide gives you the keys to understand the stakes, choose the right strategy, and avoid classic mistakes.

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Why Migration Is Non-Negotiable

SAP has announced the end of standard maintenance for SAP ECC 6.0 at the end of 2027. After that date, several scenarios:

• Paid extended maintenance until 2030 (estimated 20 to 30% surcharge on annual licence cost)
• No more security patches on unsupported versions
• Growing incompatibilities with modern peripheral systems
• Difficult recruitment: SAP ECC consultants are becoming scarce

Beyond the deadline, SAP S/4HANA brings real functional benefits: HANA in-memory database for dramatically faster calculations, modern Fiori interface, native integration of PP/MM/SD/FI processes, and new supply chain features unavailable on ECC.

ALICOG Expert Note — The end of maintenance is a constraint, but above all it’s an opportunity. Companies that migrate intelligently use it to redesign their processes. Those that migrate under last-minute pressure replicate their broken processes in the new system. The results are very different.

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The Three Migration Strategies

Strategy 1 — Greenfield (New Implementation)

Principle: Start from scratch. Configure SAP S/4HANA from the ground up, without migrating existing data and configurations.

Advantages:

• Processes entirely redesigned on SAP Best Practices
• No inherited technical debt
• Optimal scope and architecture

Disadvantages:

• Longer duration (18 to 36 months depending on complexity)
• Higher cost
• Risk of operational disruption at go-live

For whom: Companies with highly complex or outdated processes, or seeking radical transformation.

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Strategy 2 — Brownfield (Technical Conversion)

Principle: Convert the existing ECC system to S/4HANA while preserving data, configurations and history.

Advantages:

• Shorter duration (9 to 18 months)
• Business continuity maintained
• Historical data preserved

Disadvantages:

• “Technical debt” is migrated along with the system
• Limited process optimizations
• Requires data cleansing before migration

For whom: Companies with broadly sound processes and a well-configured ECC.

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Strategy 3 — Selective Data Transition

Principle: Hybrid approach. Selectively migrate relevant data while redesigning certain processes.

Advantages:

• Maximum flexibility
• Combines Greenfield and Brownfield benefits
• Can include system consolidation

Disadvantages:

• Complex to implement
• Requires deep expertise
• Intermediate to high cost

For whom: Groups with multiple ECC instances to consolidate, or companies wanting to renovate specific domains only.

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The Decision Matrix

Criterion	Greenfield	Brownfield	Selective
Current processes	Obsolete / complex	Sound	Mixed
Budget	High	Moderate	High
Acceptable timeline	24-36 months	12-18 months	18-24 months
Desired transformation	Radical	Minimal	Targeted
Historical data	Not a priority	Essential	Selective

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BPR + Migration: Why Do Both Together

The most expensive mistake we observe: companies migrating their broken processes unchanged into SAP S/4HANA. Result: a new system, the same problems, with a bill of several million euros.

SAP migration is the ideal opportunity to conduct Business Process Reengineering (BPR). Here’s why:

1. Teams are already mobilized on the project — use it to rethink processes
2. SAP S/4HANA imposes Best Practices — migration forces alignment with standards that are, in most cases, better than existing processes
3. The marginal cost of BPR is low during migration — while it would be high outside this context
4. The final ROI is incomparable — a migration with BPR generates 3 to 5 times more value than a pure technical migration

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7 Classic Mistakes to Avoid

1. Underestimating the duration An SAP S/4HANA project takes an average of 14 months for a simple SME, and 24 to 36 months for a multi-site group. Projects launched with a 9-month plan systematically slip.

2. Neglecting data quality Data migration is consistently underestimated. Poorly populated master data (routings, BOMs, safety stocks) doom the system to produce absurd results from day one.

3. Going without executive sponsorship An SAP project without senior management commitment dies at the first obstacle. The Executive Committee must be the sponsor, not merely an observer.

4. Excluding key users Key Users must be involved from the design phase, not just during testing. They validate that redesigned processes are actually feasible.

5. Ignoring change management Technology is 30% of the project. The remaining 70% is human. Training, communication, managing resistance — this determines whether the system is adopted or worked around.

6. Treating it as an IT-only project SAP S/4HANA is as much a business project as an IT one. Supply chain, production, finance, and sales must be equal stakeholders alongside IT.

7. Insufficient testing Integrated testing (end-to-end, by process) and user acceptance testing are non-negotiable. Every hour saved on testing translates into days of post go-live crisis.

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Realistic Project Timeline

Phase	Typical duration	Key deliverables
Preparation & diagnostic	4-8 weeks	As-Is documented, strategy validated
To-Be design	8-16 weeks	Redesigned processes, config blueprint
Configuration & development	12-20 weeks	Configured system, interfaces
Integrated testing	6-10 weeks	Tested scenarios, anomalies resolved
Training & UAT	4-8 weeks	Trained users, go-live decision
Go-live & hypercare	4-8 weeks	Production deployment, stabilization

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Where to Start

If your project hasn’t launched yet, here are the first concrete steps:

1. As-Is audit (2 to 4 weeks) — technical and functional assessment of your ECC: configurations, master data, interfaces, custom developments, data volume.
2. Strategy selection — Greenfield, Brownfield or Selective, based on your current processes, budget and transformation ambition.
3. Business case — quantify the migration ROI: productivity gains, reduced operational costs, savings on ECC maintenance, new feature capabilities.
4. Partner selection — a technical SAP integrator is not enough. You need a partner who also understands your supply chain business processes.

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Conclusion

2027 is two years away. For an 18-month project, the ideal launch window is now. Every month of delay reduces your margin and increases the risk of a last-minute migration under pressure.

But beyond the calendar, the real question is: do you simply want to change systems, or use this to transform your supply chain? Your answer will determine your strategy, your investment, and most importantly, your results.

Discuss your SAP S/4HANA projeContactct with Achraf ZIAT — free first conversation →

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