Retirees can look forward to the largest Social Security cost-of-living adjustment next year since 2012 - but don’t break out the champagne just yet. For many, higher Medicare premiums will take a big bite out of their raise.

The 2018 Social Security cost-of-living adjustment (COLA) will not be announced until October, but inflation trends point toward an increase of about 2 percent, according to a recent forecast by the Senior Citizens League. That would be a welcome change compared with the 0.3 percent bump in 2017, and 2016 when no COLA was made.

COLAS are determined by an automatic formula tied to the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W). From 2013 to 2015, the annual increases have ranged around 1.5 percent.

For a retiree receiving the average monthly Social Security benefit of $1,360, a 2 percent raise would translate to an increase of $27.20. But for most beneficiaries, Medicare Part B premiums are deducted from Social Security. And the impact of the Part B premium on net benefits next year will vary due to what is known as the “hold harmless” provision governing Social Security.