Custom Code Remediation: The Budget Line Everyone Underestimates

Custom Code Remediation: The Budget Line Everyone Underestimates

Years of ABAP customizations built up on ECC don't disappear during a migration — they surface, all at once, usually costing more to fix than anyone assessed up front.

Ask a system integrator what has most consistently blown up an S/4HANA budget in their experience, and “custom code” comes up more often than almost anything else. A joint Precisely and ASUG survey released in late 2025 asked organizations directly what their top barriers to migration were, and the results confirm the pattern: business process change was cited by 49% of respondents, customizations by 44%, and organizational resistance by 37%. Customizations, in other words, sit near the very top of the list — not as an edge case, but as one of the two or three defining challenges of the entire migration.

The reason custom code is so disruptive is structural. ECC systems that have been in production for a decade or more accumulate ABAP customizations the way any long-running system accumulates technical debt — gradually, incrementally, usually for good reasons at the time, and rarely documented as thoroughly as anyone would like in hindsight. S/4HANA's simplified data model and Fiori-based interface mean a meaningful share of that custom code either breaks outright, needs rewriting to work with the new architecture, or turns out to duplicate standard functionality S/4HANA now provides natively — and none of that becomes fully visible until someone does the technical assessment.