Merger assessment guidelines
The Competition and Markets Authority’s (CMA) approach to assessing mergers.
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These guidelines set out the CMA’s approach when investigating mergers.
The guidelines are designed to help businesses and their advisers assess if competition concerns might arise in a merger.
We updated these guidelines on 3 September 2026, after reviewing how we assess rivalry-enhancing efficiencies. The new version of the guidelines replaces the section on merger efficiencies. The rest of the guidelines are unchanged (except for changes to paragraph numbers where relevant).
The new guidelines will take effect from 3 September 2026 and will apply to cases where the formal phase 1 investigation commences on or after 3 September 2026.
We updated these guidelines on 18 March 2021 after consulting on updates.
Updates to this page
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Guidance on merger efficiencies updated.
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Consultation published on draft revised guidance on our approach to efficiencies
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Updated merger assessment guidelines published.
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First published.