Monthly transmission loss data (4l)

On this page, you’ll find the total volume of historic transmission losses broken down by month. 

Previously, under Special Condition 4i of our Transmission Licence - “Requirement to Report on System Transmission Losses”, we were required to publish certain information regarding transmission Losses on the National Electricity System.  From 1st April 2021, this condition has now been removed from our new RIIO-2 Licence Conditions.

In future if there is still sufficient interest, we may publish this losses information annually on our Data Portal here:

For an introduction to transmission losses and to find out how we calculate these losses, please download our guide below.

Download ‘How transmission losses are calculated’


Future transmission losses

You can find information on the drivers that impact future transmission losses in our Electricity Ten Year Statement (ETYS).

Go to electricity ten-year statement



These documents show the monthly total volume of historic transmission losses and an indication of the cost. We also provide some information on how losses are taken into account when carrying out the balancing services activity.