Return on regulatory equity: Electricity transmission (RIIO-T1)


Source: RIIO electricity transmission annual report 2017-18.

Information correct as of: March 2019

This chart is an indicator of financial performance. It shows our estimates of electricity transmission owners’ return on regulatory equity (RoRE). It is our current view of an eight-year average RoRE over RIIO-T1.

We update this chart on an annual basis. Click the ‘more information’ tab above for a summary of the latest trends, details of how to interpret the figures and for information on methodology.

Policy Areas:

  • Electricity - transmission

Data Table

Return on regulatory equity: Electricity transmission (RIIO-T1)
Network companiesCurrent eight-year view
National Grid Electricity Transmission (excl. System Operator)10.4%
Scottish Hydro Electricity Transmission10.4%
Scottish Power Transmission8.0%

More information

Return on regulatory equity (RoRE): At-a-glance summary

  • It ranges from 10.4% for National Grid Electricity Transmission & Scottish Power Transmission to 8% for Scottish Hydro Electricity Transmission.

Relevance and further info

  • RoRE helps us monitor the financial performance of network companies under the price control.
  • RoRE should be compared to the cost of equity allowed at the start of the price control. For all electricity transmission owners, this was 7.0%
  • No electricity transmission owners are forecast to earn returns below their cost of equity.
  • The numbers include the impact of the Mid-Period Review and National Grid’s voluntary deferral.


  • Our RoRE calculation measures companies’ performance for the RIIO-1 period, this includes the first five years actual return and their forecast performance for the remaining three years of RIIO-1.
  • We report RoRE values for the companies compared against the assumptions we set for RIIO-1. Our RoRE now includes their actual and forecast financing (cost of debt) and tax performance. This is a new way of reporting RoRE, and values may not be comparable with the values we have published in the past. 
  • Our calculation assumes all outputs will be delivered. 
Date correct
March 2019
Policy area