SAP ends mainstream maintenance for ECC on December 31, 2027, with paid extended maintenance available through 2030 at a 2 percent surcharge on top of the existing 22 percent base, which means every ECC organization must decide its S/4HANA path now rather than treating the deadline as distant. The choice is not whether to move but how: a technical conversion of the existing system, a greenfield reimplementation, or a selective hybrid, each with very different cost, risk, and timeline. This comparison sets out the differences between ECC and S/4HANA, the three migration paths, and an explicit rule for which path fits.
Inside This Guide
The 2027 deadline and what it means
SAP has committed to mainstream maintenance for SAP Business Suite 7, which includes ECC 6.0, through the end of 2027, followed by optional extended maintenance through the end of 2030 at a premium. After that, ECC moves to customer-specific maintenance, which provides no new fixes or legal and regulatory updates, an untenable position for most production systems. The deadline is therefore a hard planning constraint, not a soft recommendation.
The practical reading is that an organization wanting to be safely on S/4HANA before mainstream support ends needs to start the program well before 2027, because large conversions run 12 to 30 months. Treating 2027 as the start date rather than the finish date is the most common and most expensive planning error, and it is the reason our SAP ECC 2027 end-of-life strategy guide pushes organizations to decide the path early while options and negotiating power are widest.
How S/4HANA differs from ECC
S/4HANA is not a version upgrade of ECC but a re-architected product. It runs exclusively on the HANA in-memory database rather than the traditional databases ECC supported, uses a simplified data model that collapses many ECC tables, replaces the classic interface with the Fiori experience, and changes core processes in finance, materials management, and other modules. Custom code written for ECC frequently needs remediation to run on S/4HANA, and some ECC functionality is replaced rather than carried forward.
Those architectural changes are the reason a move to S/4HANA is a project rather than a patch, and they are also the source of its benefits: faster reporting, a simpler data model, embedded analytics, and a foundation for newer SAP capabilities. The depth of change is why the migration path matters so much, since it determines how much of the existing investment carries forward. The licensing implications are set out in our SAP licensing complete guide.
Three migration paths
There are three routes to S/4HANA, and the choice shapes cost, risk, and how much of the legacy estate survives. A system conversion, sometimes called brownfield, takes the existing ECC system and converts it technically to S/4HANA, preserving configuration, history, and custom code that passes remediation. A greenfield reimplementation builds a new S/4HANA system from a clean template, redesigning processes and migrating selected data. A selective or hybrid approach blends the two, carrying forward parts of the legacy system while redesigning others.
| Path | What it does | Best when |
|---|---|---|
| System conversion (brownfield) | Technical conversion of existing ECC | Processes are sound, history must be kept |
| Greenfield reimplementation | New build on a clean template | Processes need redesign, heavy custom debt |
| Selective / hybrid | Mix of carry-forward and redesign | Large, complex multi-entity estates |
Brownfield is usually faster and cheaper because it preserves the existing investment, but it carries forward technical debt and any process problems baked into the legacy system. Greenfield is the chance to redesign on standard processes and shed custom debt, but it costs more and takes longer. The right path depends on the health of the current ECC estate, which is why an honest assessment of custom code and process quality precedes the decision.
Licensing and conversion credits
Moving from ECC to S/4HANA is also a license conversion, and SAP offers contract conversion and product conversion options that credit the value of existing ECC licenses against the new S/4HANA estate. The terms of that credit are negotiable and material, because they determine how much of the prior investment carries forward versus how much net-new license must be bought. Handled poorly, a conversion can leave an organization paying twice for capability it already owns.
The conversion-credit lever: SAP's conversion programs can credit a large share of existing ECC license value toward S/4HANA, but the default offer is rarely the best available. The credit basis, the treatment of shelfware, and the new digital-access exposure are all negotiable, and getting them right can change the license cost of a migration by seven figures. Negotiate the conversion, do not accept the first proposal.
The conversion also reopens the indirect and digital access question, because S/4HANA uses the document-based digital access model that many ECC estates never adopted. An organization converting needs to size its digital-access exposure as part of the license negotiation, a topic our SAP S/4HANA conversion credits guide and the SAP practice address directly.
Cost and timeline by path
The cost and duration of a migration vary widely by path and estate complexity. The table gives representative ranges for a mid-to-large organization, recognizing that scope, custom code, and data quality move the numbers substantially.
| Path | Typical duration | Relative cost | Primary risk |
|---|---|---|---|
| System conversion | 9 to 18 months | Lower | Carried-forward technical debt |
| Greenfield | 18 to 30 months | Higher | Scope and redesign effort |
| Selective / hybrid | 18 to 36 months | Highest | Integration complexity |
Beyond the deployment model, the host decision adds another cost dimension, since S/4HANA can run on-premise, in a private cloud under RISE, or in a public cloud edition. Each carries a different cost and control profile, compared in our RISE, GROW, and HEC guide. The deployment and host decisions interact, so they are best made together rather than in sequence.
Risk and the cost of waiting
The dominant risk in the ECC-to-S/4HANA decision is not the migration itself but waiting too long to start it. As 2027 approaches, system integrator capacity tightens, skilled SAP resources become scarcer and pricier, and an organization that starts late loses the negotiating power that comes from having time and options. Extended maintenance through 2030 buys time, but at a recurring premium and without new innovation, so it is a bridge rather than a destination.
The cost of waiting is therefore both direct, in the extended-maintenance premium, and indirect, in higher implementation costs and a weaker negotiating position as the deadline nears. The organizations that come out best are those that decided their path early, used the runway to negotiate both the license conversion and the implementation, and treated the deadline as a planning anchor. The full user-type and license model that underpins the new estate is in our SAP user types reference.
Side-by-side decision matrix
| Factor | Stay on ECC | Move to S/4HANA |
|---|---|---|
| Mainstream support | Ends 2027 | Current, long-term |
| Extended maintenance | To 2030 at a premium | Not needed |
| Innovation and new features | Frozen | Ongoing |
| Database | Traditional databases | HANA only |
| Process model | Classic ECC | Simplified, Fiori |
| Cost posture | Rising maintenance, no benefit | Migration cost, then modern run |
| Best for | Short bridge only | Every organization, on the right timeline |
The verdict: choose which path when
Choose a system conversion when your ECC processes are sound, your custom code is manageable, and you need to preserve transaction history and configuration. Brownfield is the faster, cheaper route for a healthy estate, and it gets you onto S/4HANA with the least disruption, which is why it is the most common path for organizations that have run ECC well.
Choose a greenfield reimplementation when your processes need redesign, your custom-code debt is heavy, or a major business change makes a clean start worthwhile. The higher cost and longer timeline buy a standardized, lower-debt estate that is cheaper to run for years afterward. A selective hybrid fits only the largest, most complex multi-entity organizations where neither pure path is feasible.
The practical rule: The decision to move is already made by the 2027 deadline; the only real choice is the path and the timing. Assess your custom code and process health now, choose brownfield for a healthy estate and greenfield for a debt-heavy one, and start early enough to negotiate both the license conversion and the implementation from a position of time and options.
The business case beyond the deadline
Treating the migration purely as a compliance deadline understates the case and weakens the program, because a move justified only by avoiding lost support tends to be scoped to do the minimum and delivers little business value. The stronger framing is that the deadline forces a decision the organization should make anyway, and the migration is the moment to capture real operational gains: a simplified data model that speeds reporting, embedded analytics that remove separate tools, and a foundation for newer SAP finance and supply-chain capabilities.
The finance organization is usually where the benefit lands first. The S/4HANA universal journal collapses the separate ledgers and reconciliation steps that ECC carried, which shortens the close, removes manual reconciliation effort, and gives a single source of financial truth. For organizations that have struggled with a slow or fragile financial close on ECC, that improvement alone can carry a meaningful part of the business case, independent of the support deadline.
There is also a real-options value in moving while the runway is wide. An organization that converts early gains the ability to adopt new SAP capabilities as they ship, rather than carrying a frozen estate that falls further behind each year. The longer an estate stays on ECC, the larger the eventual gap to close and the more disruptive the eventual move, so an early migration is partly an investment in keeping future change small and incremental rather than large and forced.
Set against those gains is the honest cost of disruption, and a credible business case prices both. The migration consumes management attention, carries a productivity dip around go-live, and competes with other priorities for capital and skilled people. The organizations that build the strongest case are those that quantify the operational benefits rather than relying on the deadline alone, then weigh them against a realistic, contingency-loaded cost. That balanced case is what survives board scrutiny and keeps the program funded through the inevitable mid-flight pressure.
One more point of timing deserves emphasis for boards weighing the decision. The extended maintenance window to 2030 is often misread as three extra years of comfortable runway, when in practice it is a paid bridge that should be used to complete a migration already under way, not to delay starting one. An organization that waits until 2028 to begin, relying on extended maintenance, still faces the same multi-year program with less integrator capacity, higher rates, and no negotiating room, having paid the surcharge for the privilege.