Adjustment to GMC rates and WEIM administrative fees effective trade date 10/1/26

The California ISO (ISO) is experiencing year-to-date over-recovery in the Grid Management Charge (GMC) Market Services category, driven by higher-than-forecasted Extended Day-Ahead Market (EDAM) volumes.

To better align forecasted year-end collections with the budgeted revenue requirement, the ISO will decrease the Market Services rate effective Oct. 1, 2026, trade date. The adjustment is intended to reduce continued over-collection and minimize the amount that would otherwise need to be reflected in future rates.

Because the Western Energy Imbalance Market (WEIM) Services rate is derived from the Market Services rate, it will also decrease.

The chart below outlines the GMC category revenue collections forecast for the year.

Pursuant to Appendix F, Schedule 1, Part B of the ISO Tariff, the ISO will adjust the applicable GMC rate components effective Oct. 1, 2026, trade date.

All other service charge rates remain unchanged.

The ISO will continue to monitor revenue collections throughout the year and will make additional rate adjustment recommendations, upward or downward, as necessary and in accordance with the ISO Tariff. 

An updated GMC rates sheet with the new rates effective as of the Oct. 1, 2026, trade date is available on the Settlements page of the ISO website.

Contact your Customer Service representative or call ISO Customer Service at 916-608-7320 with any questions.