An ECC-to-S/4HANA migration is two projects in one: a technical transformation and a commercial re-licensing event, and the organisations that come out ahead are the ones that plan both on a single timeline rather than discovering the licensing consequences at go-live. S/4HANA is SAP's next-generation ERP, and with mainstream ECC maintenance ending, migration is on every SAP customer's agenda. This playbook lays out the migration approaches, how to sequence the work, and - the part buyers most often underplan - the licence conversion that rides alongside it. It sits beneath our SAP third-party support and ECC exit pillar.
The three migration approaches
There are three established routes to S/4HANA, and the choice shapes cost, risk, and timeline. A greenfield implementation rebuilds the ERP from a clean design, re-engineering processes and leaving legacy customisation behind. A brownfield (system conversion) migrates the existing ECC system in place, preserving processes, data, and much customisation while moving to the S/4HANA technical foundation. A selective or hybrid approach moves parts of the landscape on different timelines - for example, converting the core while re-implementing specific areas - balancing transformation against disruption.
| Approach | What it does | Best fit | Trade-off |
|---|---|---|---|
| Greenfield | New build, re-engineered processes | Heavy legacy debt; appetite for change | Largest change-management effort |
| Brownfield | Convert existing system in place | Stable, well-run ECC to preserve | Carries forward legacy complexity |
| Selective / hybrid | Mix of convert and re-implement | Large, heterogeneous landscapes | More complex to orchestrate |
Sequencing the work
Whatever the approach, a defensible sequence reduces risk. Start with discovery: a readiness assessment of your ECC system, custom code, data quality, and integrations. Move to design and a target operating model. Build and iterate in non-production, with realistic data - which is where masking and subsetting of production data matters. Test rigorously, including the integrations that touch the system indirectly. Then cut over, with a fallback plan. The technical milestones are well understood; the discipline is refusing to let the commercial workstream lag behind them.
The licence conversion question
This is the part that surprises buyers. Moving to S/4HANA is not a free continuation of your ECC entitlements - it generally requires converting to S/4HANA licensing. SAP offers contract conversion routes that translate legacy licence value into the new model, but the mapping of legacy named-user types and engine licences to S/4HANA's role-based model is where value can be lost or preserved. Done carefully, conversion can be a chance to right-size; done passively, it can lock in over-licensing. We cover the detail in mapping legacy SAP licences to S/4HANA user roles, which should be read in parallel with this playbook.
Convert on a measured user baseline, not the legacy count. The licence conversion is your best opportunity in years to align entitlements to actual usage - and your biggest risk of carrying forward shelfware. Before converting, measure how your ECC users actually consume the system, so legacy professional-user counts that no longer reflect reality are not simply translated into expensive S/4HANA roles. The conversion should be negotiated against measured usage, not accepted as a mechanical translation of what you happen to own.
Digital access comes with the move
Migrating to S/4HANA brings digital access in as the standard model for licensing indirect and automated use. Integrations that were handled under older indirect-access terms on ECC need to be considered under document-based digital access on S/4HANA. The migration is therefore the natural moment to settle your indirect-access position, ideally with a measured document baseline rather than an estimate - the mechanics are in our guides to the Digital Access Adoption Program and SAP API and indirect-access changes.
How maintenance funds the timeline
The migration does not happen instantly, and what you do about ECC maintenance in the interim shapes the budget. Staying on SAP extended maintenance keeps full vendor support but at an uplifted cost on a system you are leaving. Moving ECC to third-party support during the migration window typically lowers that interim cost and can fund the programme, at the price of forgoing new SAP releases you may not need on a system being retired. The trade-off is laid out in ECC extended maintenance vs third-party support. Either way, the maintenance decision and the migration plan share one timeline.
A buyer-side checklist
Five questions keep a migration commercially honest. Which approach - greenfield, brownfield, or selective - fits your landscape and appetite for change? What is the realistic timeline, and how will you maintain ECC across it? How will legacy licences convert, and on what measured user baseline? What is your digital-access position on the target system? And is the whole programme - technical and commercial - governed as one plan with one budget? Answer these and S/4HANA becomes a planned transformation rather than a series of unbudgeted surprises.
On-premise, cloud, and RISE
The migration approach is only half the destination decision; the other half is the deployment and commercial model for S/4HANA itself. You can run S/4HANA on-premise under perpetual licences with annual maintenance, in a private cloud, or through SAP's subscription-based transformation offering that bundles software, infrastructure, and services into a single contract. These models differ not just in cost shape - capital versus operating expenditure - but in who operates the system, how upgrades are handled, and how you are licensed and audited. A subscription model moves much of the licensing-compliance surface into the subscription terms, while an on-premise model keeps you in the familiar named-user-and-engine world. The right choice depends on your operating preferences, your appetite for vendor-managed infrastructure, and a careful multi-year total-cost comparison. Crucially, this decision interacts with the migration approach: a greenfield build lends itself to a fresh subscription commitment, while a brownfield conversion may align more naturally with carrying forward perpetual entitlements. Decide the deployment model alongside the migration approach, not after it.
For the licence conversion detail, continue to mapping legacy licences to S/4HANA roles. For the wider framing, return to the SAP third-party support and ECC exit pillar. For an engagement on your migration's commercial workstream, see our SAP licensing experts service and the SAP vendor hub.