Monthly Social Security and Supplemental Security Income (SSI) benefits for more than 66 million Americans will increase 2 percent in 2018.

In its announcement Oct.13 of the increase, the Social Security Administration said the cost-of-living adjustment (COLA) will begin with benefits payable to more than 61 million Social Security beneficiaries in January 2018. Increased payments to more than 8 million SSI beneficiaries will begin this year on Dec. 29.

Some people receive both Social Security and SSI benefits.

According to the Social Security Administration, the average monthly Social Security benefits beginning in January will be $1,404 for all retired workers, $2,340 for couples in which both people receive benefits, $1,336 for a widowed person living alone, $2,771 for a widowed mother and two children, and $1,197 for disabled workers.

The Social Security Act ties the annual COLA to the increase in the Consumer Price Index as determined by the U.S. Department of Labor’s Bureau of Labor Statistics.

Some other adjustments that take effect in January of each year are based on the increase in average wages. Under that criteria, the maximum amount of earnings subject to the Social Security tax (taxable maximum) will increase to $128,700 from the previous $127,200.

Of the estimated 175 million workers who will pay Social Security taxes in 2018, about 12 million will pay more because of the increase in the taxable maximum, officials said.

Information about Medicare changes for 2018, when announced, will be available at www.medicare.gov.