By late 2026, your executive committee is asking the same question they asked in 2024 and 2025: “When are we moving to S/4HANA?” The 31 December 2027 deadline is no longer abstract — it’s arriving fast. And yet, the most consequential decision of your transformation programme has often not been made: which migration path should you choose?
Greenfield, Brownfield, or Selective Data Transition (SDT): these three approaches are not interchangeable. Choosing the wrong one can cost you an additional 12 to 18 months, leave your ERP carrying unresolved technical debt, or deliver a programme whose complexity was underestimated by 40%. This guide helps you decide before you engage a system integrator.
The Calendar Pressure: Why the Choice Must Be Made Now
The End of SAP ECC Mainstream Maintenance: What the 2027 Deadline Actually Means
SAP has unambiguously confirmed the end of mainstream maintenance for SAP Business Suite 7 (including ECC): 31 December 2027. After that date, SAP will no longer deliver standard corrections, legal and regulatory updates, or support packages under the standard maintenance contract.
One extension option exists: Extended Maintenance to 31 December 2030, at an additional charge of approximately 2 percentage points on annual maintenance fees — raising the effective support rate from roughly 22% to around 24% of net licence value (SAP Licensing Experts, Extended Maintenance 2027-2030 analysis). In practice, initial SAP commercial proposals tend to be negotiated upward — some organisations report opening rates 30 to 50% above market.
The maintenance extension buys time. It does not resolve technical debt, the growing compatibility risk with cloud ecosystems, or the widening gap with native S/4HANA capabilities (AI, SAP BTP, SAP Joule).
Where Are SAP ECC Customers Today?
According to Gartner data cited by SAPinsider, 37% of SAP ECC customers had subscribed to S/4HANA licences by Q2 2024 — and 30% were in production on S/4HANA Cloud Private Edition in 2025, up from 19% the year before. Progress is real, but more than 60% of ECC customers had yet to migrate by early 2026, with a 24-month window remaining before the standard deadline.
For mid-market and enterprise customers running heavily customised SAP ECC with active PP/QM modules and legacy EDI interfaces — a common profile across manufacturing and distribution — timelines are particularly tight: a Brownfield project averages 12 to 18 months, and a Greenfield typically runs 18 to 30 months. Organisations that have not yet started their scoping risk missing the mainstream end-of-support date without paying for the extension.
The Risks of Standing Still
Remaining on SAP ECC beyond 2027 without extended maintenance creates three categories of risk that CIOs must present to their executive leadership:
- Security: no vulnerability patches, leaving the ERP exposed to unaddressed attack vectors on a business-critical system.
- Legal and regulatory compliance: tax and regulatory changes — including mandatory B2B e-invoicing frameworks being rolled out across the EU and UK — will no longer be integrated into standard SAP ECC updates.
- Resource scarcity: the ABAP ECC talent pool is shrinking. Integrators with S/4HANA conversion expertise are already concentrating their teams on active S/4HANA programmes. The longer you wait, the narrower the available profile window becomes.
The 3 Migration Paths Explained
Path 1 — Greenfield: Start Fresh with Best Practices
A Greenfield deployment means standing up a new SAP S/4HANA instance starting from SAP’s standard configuration (“Best Practices”), without carrying over existing ECC code or configuration. Historical transactional data is not migrated into the production system — it is archived in a cold storage system or data lake.
What you gain: a natively Clean Core system, fully enabled for SAP BTP, SAP Joule (SAP’s AI agents), and future cloud innovations. Zero technical debt carried forward. Processes are redesigned against the SAP standard, which forces a functional rethink that is often overdue.
What you lose: operational transaction history (orders, invoices, stock movements), customisations that addressed genuine business requirements, and above all, time — Greenfield projects typically run 18 to 30 months depending on functional scope.
Best suited for: organisations with a high volume of custom Z-code (more than 60% of code outside the SAP standard), an explicit ambition for end-to-end process transformation, or those that have gone through successive acquisitions that make their ECC difficult to convert cleanly.
Path 2 — Brownfield: Convert the Existing System
Brownfield, or “system conversion”, involves converting the SAP ECC instance directly to SAP S/4HANA using dedicated SAP tooling. The central tool is SUM with the DMO option (Software Update Manager + Database Migration Option): it combines, in a single guided procedure, the database migration to SAP HANA, the application version upgrade, and Unicode conversion (SAP Help, Conversion to SAP S/4HANA using SUM).
What you keep: the full history of transactional data, all customisations (Z-code, BADIs, user exits), and the organisational structure. Timeline is shorter: 12 to 18 months for a standard scope.
The main risk: you carry technical debt into S/4HANA without having addressed it. Problematic Z-code in ECC will remain problematic in S/4HANA — and it will be harder to remediate after migration than before. A Brownfield executed without prior code remediation and without a Clean Core ambition can deliver a “dirty” S/4HANA that limits activation of cloud features.
Best suited for: organisations with a relatively clean ECC (Z-object remediation rate below 30%), a constrained deadline, and a willingness to adopt Clean Core Strategy progressively after migration.
Path 3 — Selective Data Transition (SDT)
SDT — sometimes called “Bluefield” by certain integrators — is a hybrid approach: a new S/4HANA instance is built (as in Greenfield) while selectively migrating certain data perimeters and processes (as in Brownfield). Tools used include SAP LT Replication Server and the SAP Landscape Transformation family.
The advantages: maximum flexibility — you choose which processes to modernise and which historical data to bring across. For a multi-entity group with subsidiaries at different maturity levels, SDT allows one clean subsidiary to migrate as a full Greenfield while a heavily customised entity undergoes selective conversion.
The main risk: complexity is consistently underestimated. Every scope extension — an additional country, an intercompany flow, a legacy module to bring across — increases test workload and coordination exponentially. Typical timelines run from 15 to 24 months, but can extend significantly depending on scope. Cost is generally higher than a standard Brownfield.
Best suited for: groups with heterogeneous subsidiaries, recent acquisitions not yet harmonised, or mixed perimeters where some processes warrant a clean-slate rebuild and others should be preserved as-is.
The 6-Question Decision Matrix
Before deciding, work through these six questions with your internal team and your candidate integrator:
Q1 — What Is Your Volume of Z-Programs and Non-Standard Customisations?
Ask your SAP Basis team to run the Custom Code Migration Worklist (SPDD/SPAU + analysis report). If more than 40 to 50% of your code sits outside the SAP standard, Brownfield risks delivering a long-term unsupportable S/4HANA. Greenfield then becomes the more honest path.
Q2 — What Is Your Estimated Technical Debt?
The SAP EarlyWatch Alert tool — included at no additional cost in your maintenance contract and accessible via SAP for Me — generates a health report for your ECC instance (SAP Support, EarlyWatch Alert). It identifies deprecated objects, unmigrated BADIs, and risk zones. This is the first tool to activate before committing to any migration path.
Q3 — What Is Your Hard Deadline?
If you must be live before 31 December 2027, a Greenfield on a complex ECC is probably out of reach. Brownfield or a reduced-scope SDT are the only realistic options. If you are prepared to pay for extended maintenance through 2030, you regain three years of runway — but at an additional cost that needs to be modelled in your business case.
Q4 — Is Your Clean Core and SAP BTP Ambition Real or Aspirational?
SAP Joule and native SAP BTP extensions are technically activatable on a Brownfield, but their deployment is constrained if the core is not clean. If your 3-to-5-year roadmap includes genuine adoption of SAP AI and cloud extensions, Greenfield — or a Brownfield with an explicit Clean Core remediation plan — is a prerequisite.
Q5 — Is Your Scope Homogeneous or Heterogeneous?
A single-instance ECC with a stable geographic and functional perimeter lends itself well to Brownfield. A group with five ECC instances, subsidiaries across multiple regions, recent acquisitions on different SAP versions, and non-harmonised processes is a natural candidate for SDT — despite the complexity.
Q6 — What Is Your Budget and Operational Risk Tolerance?
Brownfield is generally the least expensive of the three paths, but demands a technically riskier cutover window (switching over a live ECC instance). Greenfield distributes risk over time but requires a higher total programme budget. SDT accumulates both risk types.
7-Criteria Comparison Table
| Criterion | Greenfield | Brownfield | SDT |
|---|---|---|---|
| Average timeline | 18-30 months | 12-18 months | 15-24 months |
| Relative cost | High | Medium | High |
| Historical data retention | No (archive) | Yes | Partial |
| Operational risk level | Moderate (new system) | High (live ECC cutover) | High (hybrid complexity) |
| Native Clean Core compatibility | Maximum | Conditional | Variable |
| Prerequisite for full SAP Joule/BTP | Recommended | Possible with remediation plan | Varies by scope |
| SAP recommendation for low Z-code customers | — | Priority | Alternative |
Pitfalls to Avoid on Each Path
Greenfield Without OOTB Discipline
Greenfield starts with the intention of running SAP out of the box (OOTB). In practice, functional scoping workshops generate customisation requests that business teams consider non-negotiable. If project governance lacks a decision body capable of saying no to deviations from the standard, Greenfield ends up recreating the same Z-objects under a different name. The result: a Greenfield S/4HANA with the same flaws as the ECC it replaced.
Big-Bang Brownfield on a Critical ERP During Peak Activity
The SUM+DMO conversion requires a cutover window that takes the production system offline — typically 2 to 5 days depending on data volumes. Planning this switch during a critical period (year-end close, seasonal order peak, harvest campaign for an agri-food business) is a project governance failure. Brownfield demands rigorous planning of the maintenance window.
SDT With Scope Creep
SDT’s flexibility is both its main strength and its main trap. Every additional entity brought into the migration scope — a regional subsidiary added mid-project, an intercompany flow that was not in the original scope — multiplies test cases and dependencies. SDT projects have a documented tendency to see scope expand under pressure from business stakeholders, generating timeline and budget overruns. Strict scope governance is a non-negotiable prerequisite.
What SAP Officially Recommends in 2026
RISE with SAP and GROW with SAP: Commercial Programmes, Not Technical Paths
A common source of confusion in conversations with SAP sales teams is conflating RISE with SAP or GROW with SAP with technical migration paths. These are commercial engagement programmes: RISE targets ECC customers migrating to S/4HANA Cloud Private Edition through a bundled contract (licence + infrastructure + SAP managed services + BTP credits), while GROW targets midmarket organisations on S/4HANA Cloud Public Edition. For a full comparison, read our RISE vs GROW decision guide 2026.
On the technical side, RISE with SAP supports all three migration paths. GROW with SAP is structurally tied to Greenfield (Public Edition does not support direct conversion of a customised ECC).
SAP Clean Core Strategy: The Official SAP Direction
SAP officially steers its customers toward a Clean Core posture, regardless of the path chosen. This strategy — articulated across five dimensions (processes, extensions, data, integrations, operations) — has become a prerequisite for fully activating S/4HANA’s AI and cloud capabilities. For Brownfield customers, SAP recommends integrating a Z-code remediation plan within 12 to 18 months of migration. For everything related to Clean Core strategy and its impact on your migration, read our comprehensive guide on SAP Clean Core and BTP 2026.
SAP Resources Available Before You Choose
Three free SAP tools can be activated before engaging a system integrator:
- SAP EarlyWatch Alert — an ECC health report included in your maintenance contract. Activate this first.
- SAP Transformation Navigator — a free online self-assessment tool that generates a personalised S/4HANA roadmap based on your IT landscape and business objectives (SAP Community, official blog).
- SAP Custom Code Migration Worklist — analysis of existing Z-code to estimate remediation effort based on the chosen path.
These three tools together give you the input data for an informed decision — and for a more structured conversation with candidate integrators, who will find it harder to challenge figures produced by their own tooling.
Conclusion: Decide Now, Formalise in Writing
The choice of migration path is not a decision you can delegate to your integrator. It is a strategic decision that belongs to the CIO, aligned with the CFO (multi-year budget), the CHRO (change management based on the scale of the transformation), and general management (process transformation ambition versus operational continuity).
If you are running a mid-market manufacturing or distribution organisation on a relatively clean SAP ECC instance with a hard 2027 deadline, Brownfield with a post-migration Clean Core plan is generally the most pragmatic path. If your ECC is heavily customised and your leadership is prepared to invest in genuine process transformation, Greenfield will give you a more durable system. If your group is heterogeneous and some perimeters merit being preserved, SDT can be justified — provided you build a governance structure capable of enforcing strict scope control.
The worst decision is no decision: every month of delay shrinks your migration window, increases competition for available S/4HANA profiles, and moves the standard maintenance deadline closer.
To go further and quantify the cost of inaction, read our article on how to calculate your ageing ERP’s technical debt and build a business case for your leadership. Or download our ERP evaluation grid — 30 criteria across 100 points to benchmark your situation before choosing a migration path.
