The Revised IDW S 1 (2026 Edition): Key changes and their practical implications

Published on 8 April 2026, the revised IDW S 1 (2026 edition) modernises Germany’s primary valuation standard — unchanged since 2008 — to reflect 18 years of developments in valuation practice, case law and theory. The following main changes stand at the centre of the reform: the introduction of the plausibilised decision value, the expansion of the auditor’s functions from three to four roles through the introduction of the neutral expert (‘neutraler Sachverständiger’), and the replacement of the real/pseudo synergy distinction with a unified expectability criterion. The revision also formally embeds graded plausibility requirements and links the depth of review to the selected valuation concept and auditor function. “The revised IDW S 1 (2026) is not a comprehensive overhaul, but a targeted evolution at precisely those points where the previous version could no longer reflect changed valuation practice,” write Zimny and Bahr.

The plausibilised decision value replaces the former subjective decision value and closes a longstanding gap in transaction-related engagements: for the first time, a professionally quality-assured valuation concept is available for M&A contexts, requiring both internal and external plausibility assessment. On synergies, the new expectability criterion resolves the previously difficult-to-apply distinction between real and pseudo synergies — though practitioners should note that German courts in squeeze-out proceedings still apply the old categorisation, creating a documentation tension for valuations that serve both transaction and legal purposes.

For valuation practice, the implications are clear: value concept, auditor function, and depth of plausibility assessment must be specified before work begins. Documentation requirements — particularly around synergy assumptions — rise materially across the board.

Read the full article by Gregor Zimny and Simon Bahr published in KoR, Issue 07-08, 10 July 2026, pp. 272–277.