ERP migration from SAP ECC to S/4HANA

The transition from SAP ECC (ERP Central Component, the foundation of SAP Business Suite since the early 2000s) to SAP S/4HANA is the largest ERP programme most German Mid-Market operators will run this decade. The deadline is no longer theoretical: SAP's mainstream maintenance for ECC ends in 2027, with extended maintenance available until 2030 at a meaningful premium and no SAP-backed support thereafter. Around 30,000 customers globally still run ECC, with several thousand of those headquartered in DACH, and the migration window is closing fast. This guide frames the three viable migration paths — greenfield, brownfield and bluefield/selective — with realistic timelines, cost ranges, partner-selection criteria and the failure modes that derail Mid-Market programmes most often. It is written for finance directors, IT directors and programme sponsors who need a clear-eyed view of what they are getting into.

Why migration is unavoidable

SAP's commitment to ECC ends in two visible steps. Mainstream maintenance, which covers regulatory updates and full support, ends on 31 December 2027. Extended maintenance, with a meaningful surcharge on the maintenance base, runs until 31 December 2030. After 2030, ECC will receive no SAP-backed updates — including no further regulatory patches for German tax law, e-invoicing mandates such as the rolling out of mandatory B2B e-invoicing in Germany from 2025/2027, or ESG reporting obligations under CSRD. Beyond the maintenance cliff, the platform reality is unforgiving: S/4HANA runs only on the SAP HANA in-memory database; ECC's traditional row-store databases (Oracle, IBM Db2, MS SQL) are not a forward path. The HANA shift forces a database migration regardless of the functional migration approach. The economic case is therefore not whether to migrate but when and how: deferring into 2029 or 2030 leaves no contingency for the inevitable timeline overruns and pushes the organisation into extended-maintenance pricing for the duration. Most Mid-Market programmes that started in 2024 or 2025 will only just complete by the 2027 mainstream cut-off; programmes starting in 2026 are effectively committed to extended maintenance for at least one year.

The three migration paths

SAP and the analyst community recognise three viable migration paths. Greenfield means a complete re-implementation: a fresh S/4HANA system is built to SAP Best Practices, business processes are realigned to the standard, master and transactional data are migrated selectively, and the old ECC system is retired. Greenfield maximises clean-core discipline and process simplification but discards the customisation and configuration accumulated over fifteen or twenty years. Brownfield, also called system conversion, is a technical in-place upgrade using the SAP Software Update Manager (SUM) toolchain with the Database Migration Option (DMO) for the move to HANA. The existing customer code, configuration and data move to S/4HANA, then simplification happens incrementally afterwards. Brownfield preserves investment but inherits accumulated technical debt. Bluefield, also called selective data transition, is a hybrid using third-party tools (SNP CrystalBridge, cbs ET, Datavard) to copy selected configuration, customisation and data from ECC into a freshly installed S/4HANA system, allowing the customer to keep what is valuable and leave the rest behind. Bluefield combines the cleanliness of greenfield with significant investment preservation, at a higher tooling and consulting cost. For the German Mid-Market, brownfield is by some distance the most common path, chosen by roughly 60 to 70 per cent of mid-market programmes; greenfield typically suits organisations with very high custom-code volume and a willingness to redesign processes; bluefield is gaining ground for upper-mid-market customers who want a structured middle option.

Critical preparation steps

Three preparation streams determine whether a migration runs to plan. Custom-code remediation is the first and most underestimated. ECC customers typically run between 5,000 and 50,000 custom ABAP objects accumulated over years; a significant minority of these are incompatible with HANA, with S/4HANA simplifications, or with the new data model. SAP's ABAP Test Cockpit (ATC) and the Usage Procedure Logging (UPL) capability identify which custom objects are actually used and which are HANA-incompatible. Best practice is to retire 30 to 50 per cent of custom objects (the unused tail) and remediate the rest before the technical conversion. Data-volume reduction is the second. Years of transactional history bloat the ECC database; archiving and selective deletion before the HANA migration cuts downtime, reduces hardware sizing for HANA, and lowers ongoing licence costs (HANA is sized on compressed data volume). Business-partner conversion is the third and most disruptive structural change. In ECC, customers and suppliers live in separate master tables (KNA1 for customers, LFA1 for suppliers); in S/4HANA they are unified under the Business Partner (BUT000) framework. The conversion must be planned, simulated multiple times in test systems, and aligned with downstream interfaces. Beyond these three, every Mid-Market programme should also run a Custom Code Migration Worklist and a Simplification List analysis (SAP Note 2502552) to scope process and code changes by S/4HANA release.

Realistic timelines and costs

A typical German Mid-Market brownfield programme for a 500- to 1,500-user ECC system runs 12 to 24 months end-to-end: 3 to 6 months for assessment, custom-code analysis and architecture decisions; 6 to 12 months for technical conversion, custom-code remediation and testing; 3 to 6 months for hyper-care and post-go-live stabilisation. Greenfield programmes at comparable scope run 18 to 36 months because the process redesign and data-migration design phases are substantially longer. Bluefield typically sits between the two at 15 to 30 months. Cost ranges for a 1,000-user Mid-Market programme: brownfield typically EUR 4 to 10 million all-in including licence, infrastructure, partner services and internal effort; greenfield EUR 8 to 20 million; bluefield EUR 6 to 14 million. The licence-conversion question is its own gotcha: perpetual ECC licences with annual maintenance convert to S/4HANA subscription (Cloud Public, Cloud Private or RISE-with-SAP), which is operationally simpler but typically increases the licence run-rate by 30 to 80 per cent over five years. On-premises S/4HANA remains available and is the closest economic equivalent to the ECC perpetual model for customers who genuinely cannot move to a cloud commercial structure. RISE-with-SAP bundles licence, infrastructure and managed services and is now the default for new S/4HANA programmes at most Big-4 and SAP-anchored partners.

Common failure modes and partner selection

Three failure modes account for the majority of distressed S/4HANA programmes in the German Mid-Market. Under-budgeted custom-code remediation: programmes start with a custom-code count that turns out to be 30 to 50 per cent higher in practice, and remediation effort balloons in mid-project. Ignored data-quality issues: the business-partner conversion exposes years of duplicate, inconsistent or orphan records that nobody had time to clean while ECC was running; the cleanup happens under migration pressure rather than in calm preparation. Insufficient business-process alignment: technical brownfield conversions deliver S/4HANA without a process redesign, leaving the organisation with the same workflows on a more expensive platform — the business value never materialises. The partner-selection landscape splits into three tiers. Big-4 firms (Deloitte, EY, KPMG, PwC) bring scale, methodology and global reach but are expensive and may not engage senior staff on mid-market programmes. SAP-anchored specialists (All for One, NTT DATA Business Solutions, abat, Camelot, FIS) typically offer the best price-quality balance for German Mid-Market programmes and bring deep S/4HANA-specific tooling. Regional Mid-Market consultancies can be excellent for smaller, well-scoped brownfield conversions but lack scale for greenfield or multi-country programmes. The decisive criteria are: number of comparable S/4HANA migrations completed in the last 24 months, named senior consultants committed by contract, and a willingness to put fixed-fee structure on the technical conversion phase.

Practical recommendation for the Mid-Market

For a typical German Mid-Market ECC customer with 500 to 1,500 users, 10,000 to 25,000 custom objects, and a stable industry-standard process landscape, the pragmatic recommendation is a disciplined brownfield programme with selective greenfield for new business units or recently acquired entities. The reasoning: brownfield protects the configuration and master-data investment, the technical conversion is well-tooled (SUM with DMO), the timeline is the most predictable of the three paths, and the cost envelope is the most controllable. The selective-greenfield carve-out for new entities prevents the migration from importing decades of accumulated complexity into otherwise clean operations. Customers who can credibly retire most of their custom code — either because the business has changed substantially or because the customisation was always more cosmetic than essential — should consider a RISE-with-SAP greenfield, accepting the longer programme in exchange for a cleaner long-term operating model. Customers who genuinely sit between the two should evaluate bluefield with SNP or cbs, accepting the higher tooling cost in exchange for structured investment preservation. In all three cases, the most important decision is timing: start the assessment in 2026 to be safely live before the 2027 mainstream cut-off, or accept at least one year of extended-maintenance premium and the operational risk of running mission-critical processes on a soon-to-be-unsupported platform. The cost of starting too late is materially higher than the cost of starting too early.

Also consider:SAP Business One · Oracle Fusion Cloud ERP

Häufig gestellte Fragen

By when do I have to migrate from SAP ECC to S/4HANA?

Mainstream maintenance for SAP ERP 6.0 (ECC) with Enhancement Packages 6 to 8 ends on 31 December 2027; paid extended maintenance prolongs support until the end of 2030 for a surcharge of about two percentage points on the maintenance fee (for releases without or with EHP 0-5, maintenance already expired at the end of 2025). For complex existing customers, SAP additionally offers an ERP Private Edition transition option under which ECC can continue to run with support until the end of 2033 after moving to an SAP-managed RISE private cloud environment and migrating to the HANA database. Since migration projects take roughly 9 to 48 months depending on size, mid-sized companies should make the decision well before 2027 and large corporations should start correspondingly earlier. Those who let the deadline and extension options pass unused will subsequently depend on expensive third-party or custom maintenance.

What is the difference between brownfield, greenfield and selective data transition?

In a brownfield conversion, the existing ECC system is technically converted to S/4HANA using SAP tooling (DMO in the Software Update Manager), with customising, data and custom code largely preserved. Greenfield means a complete re-implementation based on SAP Best Practices, in which legacy baggage is cleaned up but existing customising is lost and data migration is more elaborate. Selective data transition (also called bluefield) is a hybrid form in which a new system is built while selected historical data and valuable custom logic are deliberately carried over. Which path fits depends on the quality of the existing processes, the volume of custom code and the audit requirements.

How much does an S/4HANA migration cost and how long does it take?

Durations range from about 9 to 18 months for a brownfield conversion in the mid-market to 30 to 48 months for a greenfield migration in a multi-country corporate group. Total costs cover licences, implementation, training and cloud/hardware expenditure and, in the mid-market, lie roughly between half a million and several million euros, while corporate projects can reach double-digit millions. The licence usually accounts for only about 15 to 30 percent of total costs; the largest block consists of consulting, internal effort and custom code adaptation (together often 45 to 60 percent). Note that daily rates for S/4HANA specialists have recently risen by around 30 to 50 percent due to scarce availability, making projects even more expensive.

Should we run S/4HANA as public cloud, private cloud or on-premise?

The public cloud (via GROW with SAP) is standards-driven and cheaper, but severely restricts customising (extensions only via defined frameworks, no backend GUI access) and is primarily suited to companies with standardised processes. The Private Cloud Edition via RISE with SAP runs as a single tenant in an SAP-managed hyperscaler environment and allows full ABAP development as well as carrying over existing Z-code, BAdI and extension logic from ECC, which is why it is the preferred route for many existing customers with historically grown customising. The on-premise variant with your own infrastructure and perpetual licence offers maximum control but entails the highest in-house operations and infrastructure effort. Mid-sized companies mostly start with public or private cloud, while on-premise tends to remain reserved for special cases with particular data sovereignty or compliance requirements.

What happens to our custom code and Z-objects during the migration?

Before any conversion, a custom code inventory should be run via the ABAP Test Cockpit (ATC) against the S/4HANA simplification items, which frequently produces many findings and forms the basis for the effort estimate. In the brownfield approach, custom code is carried over as part of the conversion; many standard findings can be resolved via quick fixes in the ABAP Development Tools, but numerous routines must be adjusted manually because the data model has changed (for instance through the Universal Journal with the ACDOCA table). In the greenfield approach, custom code is not carried over; instead the logic is re-implemented, ideally as clean extensions via BAdIs or ABAP Cloud. Experience shows that custom code effort is the most frequently underestimated item, because the business value of many Z-objects can no longer be assessed after all the years.

How much does the user experience change with Fiori?

S/4HANA relies on the role-based SAP Fiori interface, which differs markedly from the classic, transaction-oriented SAP GUI, even though many GUI transactions remain accessible via the Fiori Launchpad. User acceptance depends heavily on early and continuous training, because navigation, search and reporting logic change and the new embedded analytics functions only reveal themselves with practice. If training starts only a few weeks before go-live, productivity often drops noticeably after the cutover. It is advisable to involve key users early, prepare role-specific launchpads and plan intensive hypercare support for the first four to eight weeks.