Social Security’s annual inflation adjustment is one of the program’s most valuable features. But it’s time to adjust the adjustment.

Retirees will get a 1.7 percent bump in their Social Security benefit next year, according to the Social Security Administration, which announced the annual cost-of-living adjustment (COLA) on Wednesday. Recipients of disability benefits and Supplemental Security Income also will receive the COLA.

That reflects continuing slow inflation in the economy -- the COLA has averaged 1.6 percent over the past four years - but it's not enough to keep up with the higher inflation retirees face.

My in-box fills up with angry e-mail messages about the COLA every year. So if you’re gearing up to accuse Washington politicians of conspiring against seniors, please note: By law, the COLA is determined by a formula that ties it to the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W), which is compiled by the U.S. Bureau of Labor Statistics (BLS).

There is good news about this year’s COLA: Beneficiaries will keep every penny. There won’t be any offset for a higher Medicare Part B premium, which typically is deducted from Social Security payments. The premium will stay at $104.90 for the third consecutive year.

Still, the COLA formula should be revised as part of the broader Social Security reform that Congress must tackle. Many economists and policymakers say the CPI-W doesn’t measure retiree inflation accurately.

“From an ideal math perspective, what you want is a calculation based on an index that matches retirees’ cost of living," says Polina Vlasenko, a senior research fellow at the American Institute for Economic Research. “The CPI-W is constructed to measure spending patterns of urban wage earners, and it’s pretty clear that retired people spend differently than wage earners.”

A recent national survey by the Senior Citizens League illustrates the cost pressures seniors, especially those living on fixed, lower amounts of income, face. Half of retirees said their monthly expenses rose more than $119 this year, while an even higher percentage (65 percent) said their benefits rose by less than $19 per month.

Other research by the group, based on BLS data, shows that Social Security beneficiaries have lost 31 percent of their buying power since 2000. Among big-ticket items, the largest price hikes were for property taxes (104 percent), gasoline (160 percent), some types of food and healthcare expenses.

Low COLAs also cut into future benefits for Americans who are eligible for benefits (ages 62 to 70) but haven’t yet filed. When you delay taking benefits until a later age – say, full retirement age (66) - you get full benefits increased by the COLAs awarded for the intervening years.