Offshore electricity transmission
Decision on 2025-26 Interest During Construction rates for offshore transmission projects and cap and floor interconnectors
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This republished letter sets out our decision on the specific Interest During Construction (IDC) rates that will apply to those offshore transmission (OFTO) projects and electricity interconnectors granted the cap and floor regime that reach Final Investment Decision (FID) during 2025-26.
- OFTO projects – to set the IDC rate capped at 9.74% (pre-tax, nominal) for projects reaching FID in 2025-26 (9.48% in 2024-25).
- Window 3 interconnectors – to set the IDC rate at 5.37% (vanilla, real-CPIH) for projects reaching FID in 2025-26 (5.38% in 2024-25).
Main document
[Decision on Interest During Construction rates to be applied during 2025-26 to offshore transmission projects and electricity interconnectors granted the cap and floor regime [PDF, 236.95KB]
](https://www.ofgem.gov.uk/sites/default/files/2025-03/IDC-25-26-letter-final.pdf)