Brownfield or greenfield: a four-question test before your S/4HANA program

Every S/4HANA program eventually arrives at the same fork: brownfield (carry the existing instance forward) or greenfield (rebuild from scratch). The honest answer is almost always somewhere in between, and the framing dominates the program for the next two years.

We ask four questions before recommending a path. None of them are 'how clean is your data', that's a downstream question.

1. How much custom code is load-bearing?

Custom code count is a vanity metric. What matters is which custom code is actually called by business processes the company can't change. We profile the production system for two weeks before kickoff, ranking objects by call frequency. Programs that can rewrite or retire 70%+ of load-bearing custom code get a greenfield recommendation; programs where load-bearing custom is high and tied to regulator-defined processes lean brownfield with selective replacement.

2. Is the master data lineage worth keeping?

Brownfield carries 14 years of master data lineage forward, including the bad parts. If your customer master, vendor master, and financial dimensions are well-governed, that's an asset. If they're a graveyard of inactive records and merger artifacts, greenfield gives you a one-time chance to fix it. Most companies underestimate how rarely they get this chance.

3. What's the regulator-driven freeze window?

Banks, hospitals, government entities and regulated manufacturers have hard windows where systems can't change. If your fiscal close, regulatory reporting cycle or accreditation review falls inside the program timeline, plan around it from week one. Greenfield is friendlier here because you can run parallel; brownfield forces a single cutover.

4. What is the team's appetite for process change?

Greenfield is a process-change program with technology delivery attached. Brownfield is technology delivery with selective process change. If the executive sponsor isn't ready to drive process change through 200+ functional users, don't pretend the program is greenfield.