Hawaiian Electric Co. is adjusting its base rate to reflect savings from the new federal tax bill, resulting in a lower monthly electrical bill for Oahu customers.

The freshly calculated savings passed on from HECO’s lower tax bill will more than offset the 2.3 percent increase the Public Utilities Commission granted HECO last month, the first increase to base rates in six years.

That adjustment translated to an increase of $2.60 for a residential bill for 500 kilowatt-hours. The latest adjustment translated to a monthly savings of $3.36 for the same kilowatt- hours, producing a net savings of 76 cents from what the rate was prior to the February increase.

Hawaiian Electric made similar rate reductions in 1987 and 1989 following changes to federal tax law.

The PUC has yet to set the effective date of the new rate for Oahu customers. HECO was given until Friday to file its updated tariffs for final regulatory review. HECO said tax savings for Maui Electric and Hawaii Electric Light customers are still being determined, and subsequent rate adjustments will require regulatory approval.