MHHS Timeline
Industry ReformsThe phased schedule for Market-wide Half-Hourly Settlement, running from go-live on 22 September 2025 to all meters migrated by 7 May 2027.
Market-wide Half-Hourly Settlement is not a single switch-on. It is a multi-year migration managed by Elexon as programme manager, with industry-wide milestones. Knowing where the programme sits helps explain why some meters already settle half-hourly while others still use estimated profiles.
Key milestones:
| Milestone | Date | What happens |
|---|---|---|
| Go-live | 22 Sep 2025 | Industry code changes take effect; supply number format moves to 22 digits |
| First migrations | 22 Oct 2025 | Suppliers begin moving meters to half-hourly settlement |
| Load Shaping Service live | Oct 2025 | Replaces D0018 profile coefficients for load shapes |
| All suppliers qualified | 28 Oct 2026 | Target for every supplier qualified to operate under MHHS |
| All meters migrated | 7 May 2027 | Target for the full meter population on half-hourly settlement |
| Shortened settlement | 2 Jul 2027 | The reconciliation timetable shortens |
Why it runs in phases: Around 30 million meters must move without disrupting settlement. Suppliers qualify, then migrate portfolios in tranches. During the transition, legacy and MHHS reference data coexist, which is why systems must handle both 21 and 22-digit supply numbers.
The practical read: Until a meter migrates, it still settles on estimated profiles and keeps its legacy Profile Class. After migration it moves to Profile Class 00 and settles on actual half-hourly data. Reconciliation of pre-migration periods continues for months after, so legacy reference data stays relevant into 2028.
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