Brownfield vs greenfield for S/4HANA: a decision tree

If you can keep your ECC configuration and most of its history, a system conversion (brownfield) is usually the shortest route to S/4HANA. If you need to shed history, redesign core processes or untangle a messy organizational structure, look at a new implementation (greenfield) or a selective data transition. The path you pick sets your test scope more than almost any other decision in the program, so make it on evidence. For the full map of the move, start with our ECC to S/4HANA migration guide.

Three technical paths, three different test loads

SAPinsider frames the technical choice as one of three routes from ERP 6.0 to S/4HANA: system conversion, new implementation and selective data transition. Each route carries a different data scope, a different custom code outcome and a different regression burden.

Question	System conversion	New implementation	Selective data transition
What moves	Whole system, configuration, code and history	Master data and open items into a rebuilt design	A shell or mix-and-match build, plus the data slices you choose
Custom code	Converted and adapted in place	Rebuilt against standard processes	Only the parts you carry across
Duration reference	ASUG 2026 brownfield average: 15.8 months	ASUG 2026 greenfield average: 20.2 months	No separate ASUG 2026 average found; plan against your data scope
Main test burden	Full regression of retained processes and simplification items	End-to-end testing of the new design plus data load rehearsals	Reconciliation of the selected slice plus regression of carried-over configuration

Decide the technical path before you look at the contract

Your commercial model does not answer the path question. The RISE or GROW contract governs how you buy and host the system, while the conversion method governs what changes inside it. SAPinsider makes the same split in its ECC to S/4HANA path comparison, and I agree with it. Teams that let the hosting deal drive the design usually discover the mismatch during blueprint, when it is expensive to fix.

Walk the decision tree

Use the three questions below in order. They are a starting filter for the steering committee, not a substitute for a Readiness Check and an honest data profile.

1. Do you need to keep your ECC configuration and history?Yes → go to question 2 · No → go to question 3
2. Is it a single instance with custom code you can live with?Yes → System conversion. Reference: ASUG 2026 brownfield average of 15.8 months. Test burden: full regression of retained processes · No → Selective data transition. No separate ASUG 2026 average found; test burden: reconciliation of the selected slice plus regression of retained configuration
3. Are SAP standard processes acceptable to the business?Yes → New implementation on SAP S/4HANA Cloud, public edition. Reference: ASUG 2026 greenfield average of 20.2 months (ASUG does not split public from private). Test burden: end-to-end on the standard scope plus data load rehearsals · No → New implementation on Cloud ERP Private or on-premise. Same reference; test burden adds custom build and interface testing

Two cautions on reading the tree. First, question 2 is where most teams stall, because "acceptable custom code" needs a number from the Readiness Check and the custom code scan, not an opinion from the ABAP lead. Second, the ASUG durations are averages across members, so your own scope decides where you land inside or outside them.

What the benchmarks say, and what they do not

In ASUG's 2026 research, brownfield was the most common approach at 47%, and greenfield took the longest on average. The same study puts brownfield at 15.8 months and greenfield at 20.2 months, against an overall average go-live of about 1.4 years, according to SAPinsider's read of the same data.

Those averages are not a plan. The three biggest scope factors SAPinsider's 2025 respondents named were the complexity of the existing data landscape, custom code that must be replaced or re-engineered, and data harmonization and cleansing. Those three are exactly what question 2 of the tree is asking about.

The ISG research points in a similar direction from a different sample. ISG reports that six in ten S/4HANA migrations miss both the projected budget and the deadline. Its split across approaches was different from ASUG's, with brownfield at 34%, greenfield at 18% and a hybrid middle ground at about half, so do not treat any one survey's mix as the market.

Deadlines that narrow the choice

Mainstream maintenance for SAP ERP 6.0 and the other Business Suite 7 core applications ends in 2027, with extended maintenance available through 2030. That is about 14 months from today, which is less time than a greenfield program averages. Extended maintenance carries a premium on the maintenance basis, so a slow path also costs money.

SAP's Transition Option is the piece that teams misread. SAP says systems must move to SAP ERP, private edition on SAP HANA before 31 December 2030, with a minimum system size of 2 TB and the max success plan. SAP's October 2026 update still describes a time-bound subscription running from 2031 through 2033, while an SAP community post now describes the window as extended through 2035. Check the current SAP note against your contract before you rely on either date.

Pricing is the other open point. SAPinsider reports that customers who committed by the end of 2025 can switch in 2031 on comparable terms, 2026 sign-ups face a 20 percent uplift, and the uplift for 2027 and later has not been disclosed. My practitioner view: treat the Transition Option as a contingency for a system that is already on a HANA-based private edition path, not as the reason to choose a slower conversion. For the wider dates, see our ECC end-of-maintenance guide.

Selective data transition: choose it only when you can name the data

Selective data transition is an alternative to both a system conversion and a new implementation. SAP's own engagement page describes it as a value-based selection that can move relevant data regardless of status, including closed items.

In practice, SAP's Community blog describes two build patterns: a shell conversion that starts from a copy without master and transaction data, and a mix-and-match build on a new S/4HANA install. Both still need a full data migration of master data, balances and open items. Hybrid variants add a warning that matters for testing: historical transactions cannot be moved with standard posting methods, so only current open orders, open items, balances and stock transfer.

Before you sign a selective path, write down four things: the company codes in scope, the history rule (for example, a two-year slice plus open items), the reconciliation totals per object, and the list of configuration you are carrying across. If any of the four is blank, you are not ready to pick this route. Our free course on transition paths walks through the same trade-offs in more depth.

What each path asks of your test team

• System conversion: regression across every retained process, plus targeted tests for each simplification item that touches your custom code. Plan the SPDD and SPAU adjustments as test items, as our SPDD and SPAU guide explains.
• Selective data transition: a reconciliation test for each migrated slice, business partner and customer-vendor checks before the first postings, and regression on the configuration you carried across.
• New implementation: a process test of the rebuilt design, repeated data load rehearsals and a fit-to-standard evidence trail that shows which gaps you accepted.

Whatever path you pick, the test plan has to be written against the same scope list. Our phase-by-phase testing plan covers how to turn the path decision into test cases and entry and exit criteria.

Frequently asked questions

Is system conversion always faster than greenfield?

Usually, but not always. ASUG's 2026 averages put brownfield at 15.8 months and greenfield at 20.2 months, yet the spread around those averages is wide. A brownfield project with heavy custom code and a messy data landscape can run longer than a greenfield project with a narrow scope.

Can we switch from conversion to a new implementation after the blueprint?

You can, but expect the data scope, the test scope and the cutover plan to be rebuilt. Make the choice before the blueprint closes, and record the reasons so the steering committee can see what changed if the decision is revisited.

Does choosing RISE with SAP force a particular path?

No. SAPinsider describes RISE as a cloud and commercial offering that leaves the technical route open. You can run a conversion or a new implementation under RISE, and the test obligations follow the path, not the contract.

Do I need the Readiness Check before choosing a path?

Yes. Run the Readiness Check and the Simplification Item Check on a production-like copy before the steering decision, since they show the custom code and simplification load that question 2 depends on. Our guide to running and reading the Readiness Check shows how to do this. Keep the output in your decision record.

Sources

1. Navigating Your RISE with SAP Journey: Updates for SAP ERP, Private Edition, Transition Option, SAP News Center, August 2025
2. Planning Beyond 2030: What SAP Business Suite 7 and SAP NetWeaver Customers Need to Know, SAP News Center, October 2026
3. Navigating Your Path to SAP Cloud ERP Private, SAP Community, 2026
4. SAP Support Deadlines Companies Should Be Planning for Now, SAPinsider, 2026
5. SAP S/4HANA Migration Timelines: The Average, the Range, and the Factors Behind Both, SAPinsider, 2026
6. How are ERP customers faring with AI readiness? ASUG research reveals that S/4HANA migrations are accelerating, diginomica (ASUG research), 2026-10-06
7. Six out of ten SAP migrations exceed budget and deadline, ITdaily (ISG 2026 State of SAP Migrations), 2026-02-06
8. ECC to S/4HANA: Brownfield, Greenfield, or Selective Data Transition?, SAPinsider, 2026
9. Move to SAP S/4HANA with Selective Data Transition, SAP Community, updated December 2025
10. Selection of optimal scenario for Selective Data Transition to SAP S/4HANA, SAP Community, 2026
11. Selective Data Transition Engagement, SAP Support
12. Conversion Guide for SAP S/4HANA 2025 (Document Version 3.0, FPS02), SAP Help Portal, 2026-10-07