The most common mistakes organisations make during SAP S/4HANA migration are underestimating data quality issues, starting data migration activities too late, neglecting change management, rushing cutover planning, and failing to align the implementation approach with the organisation’s actual situation. These mistakes are not rare edge cases — they show up repeatedly across industries and company sizes. The sections below break down each one and explain what you can do differently.
Why do so many SAP S/4HANA migrations go over budget?
SAP S/4HANA migrations go over budget most often because the initial scope is underestimated and the organisation’s actual readiness is never properly assessed before commitments are made. Without a clear baseline, teams discover complexity mid-project, forcing unplanned work, extended timelines, and additional resources that were never budgeted for.
The root cause is usually a missing starting point. Organisations jump straight from decision to roadmap without understanding where they actually stand. A maturity assessment changes that. It gives you a realistic picture of your processes, data, systems, and people before a single euro is committed to implementation. That clarity directly reduces the risk of budget overruns because the scope is grounded in reality, not assumptions.
Other common budget drivers include poor requirements definition, scope creep from stakeholders who were not involved early enough, and underinvestment in testing. When test management is treated as a final-stage checkbox rather than an ongoing quality activity, defects surface late and cost significantly more to fix. Integrating test management from the start of the programme protects both quality and budget.
What happens when data migration is not planned early enough?
When data migration is not planned early enough in an SAP S/4HANA project, teams face data quality issues, incomplete mappings, and failed test loads that push go-live dates back. Data migration is not a technical task you hand off at the end — it is a workstream that needs to run in parallel with the rest of the programme from the beginning.
Starting late means there is no time to cleanse legacy data properly. Duplicate records, inconsistent formats, and missing fields that look manageable in an ERP export become serious blockers when you try to load them into S/4HANA. The later these issues surface, the more pressure they put on the entire programme.
A structured approach involves an As-Is/To-Be analysis of your current data structures early in the project. This tells you what data you have, what condition it is in, and what needs to change before migration. Rigorous testing procedures — running multiple mock migration cycles — then validate that the data loads correctly and completely before you ever get to cutover. This is exactly how we approach data migration management: with the goal of protecting data integrity at every step, not just at the end.
How does poor change management affect SAP go-live success?
Poor change management is one of the leading reasons SAP go-live projects technically succeed but operationally fail. The system goes live on schedule, but users do not adopt it, workarounds multiply, and the business case never materialises. Change management is what bridges the gap between a working system and a working organisation.
The mistake most organisations make is treating change management as a training programme. Training tells people how to use the system. Change management addresses why the change is happening, what it means for different roles, and how to support people through the transition. Without that, resistance builds quietly and surfaces as low adoption, data entry errors, and frustrated teams after go-live.
Effective change management starts during the design phase, not the week before go-live. It involves identifying impacted roles early, communicating clearly and consistently throughout the programme, and building advocates inside the business who can support their colleagues. Post-go-live, the work continues — monitoring adoption, resolving issues quickly, and providing ongoing support as people build confidence in the new system.
What cutover planning mistakes cause the most go-live disruptions?
The cutover planning mistakes that cause the most go-live disruptions are starting too late, underestimating the time required for individual tasks, and not running realistic rehearsals before the actual cutover weekend. When any of these go wrong, organisations face extended system downtime, data inconsistencies, and operational chaos at exactly the moment when the business needs everything to work.
Cutover is the most compressed, highest-risk phase of any SAP S/4HANA migration. Every task has a dependency, and most of them have a hard deadline. A common mistake is building a cutover plan on paper without testing it against reality. Mock cutovers — full rehearsals that simulate the actual sequence under realistic conditions — reveal timing gaps and technical issues that cannot be found any other way.
Other mistakes include not defining clear go/no-go criteria, failing to assign ownership for each task, and not planning for contingencies. If something goes wrong at 2am on cutover night, you need a decision-making process that is already agreed upon, not one you are inventing under pressure. We manage cutover end-to-end, including real-time monitoring during the transition window and hypercare support in the days immediately after go-live, so operational continuity is never left to chance.
Should organisations choose greenfield or brownfield for S/4HANA migration?
Organisations should choose greenfield when they want to redesign their processes from scratch and move away from legacy customisations, and brownfield when they need to preserve existing configurations and move to S/4HANA faster with less disruption. Neither approach is universally better — the right choice depends on your business complexity, timeline, budget, and appetite for change.
What greenfield means in practice
A greenfield implementation treats S/4HANA as a clean start. You adopt SAP’s standard best-practice processes rather than replicating what you had before. This takes longer and costs more upfront, but it removes technical debt and gives you a modern, maintainable system. It works well for organisations that have outgrown their current setup or are undergoing significant business model changes.
What brownfield means in practice
A brownfield conversion moves your existing SAP ECC system to S/4HANA while keeping your current configurations, data, and customisations largely intact. It is faster and less disruptive, but you carry forward any inefficiencies that already exist. Brownfield suits organisations that need to meet a deadline, have a stable process landscape, or cannot absorb the disruption of a full redesign.
In practice, many organisations take a hybrid approach — converting the core system while selectively redesigning specific processes that are genuinely broken. The decision requires an honest assessment of your current state, which is why a maturity assessment is a useful starting point before committing to either path. We support both approaches across SAP, Microsoft Dynamics 365, and other ERP environments, covering our full range of services from programme management and data migration through to change management.
How Optinus helps with SAP S/4HANA migration
We work with multinational organisations navigating complex SAP S/4HANA migrations — and we cover the full journey, not just individual phases. That means you get one partner from maturity assessment through to post-go-live hypercare, without handover gaps between specialisms.
- Maturity assessment to establish a clear baseline before any roadmap or budget is committed
- Programme and project management with consultants who have hands-on experience of real SAP migrations at leading multinationals
- Data migration management using As-Is/To-Be analysis and rigorous testing to prevent data loss and errors
- Cutover management with meticulous planning, mock rehearsals, real-time monitoring, and hypercare included
- Change management that drives genuine user adoption, not just training delivery
- Available on-site and remote, across the Netherlands, Belgium, and internationally
If you are planning or already running an SAP S/4HANA migration and want a partner who covers the full spectrum, get in touch with our team or learn more about what we do.
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