Two-thirds of Americans are restricting their spending, according to a monthly survey, an ominous sign for retailers as they stock shelves for the holiday season. Of those limiting their spending, 32 percent say stagnant income is the main reason (the same portion that said so last year), another 29 percent cite the need to save more, and 16 percent say they worry about the economy.

“Sustainable growth in household income is the missing ingredient from this economic recovery and the leading culprit for why consumers are holding back on monthly spending,” said Greg McBride, chief financial analyst.

Surveys trying to gauge how Americans will spend money this year have given mixed reviews. The closely watched consumer confidence index from the Conference Board fell in September after rising each of the previous four months. Consumers say they are less confident about job growth, according to the index. Meanwhile, the University of Michagan's consumer sentiment index rose to a 14-month high in September with consumers reporting improved outlooks on the U.S. economy. Consumer spending accounts for about 70 percent of the nation's economic output. 

According to Bankrate, young adults just entering the workforce are the most likely to say they limit their spending to save more. Among millennials (18- to 29-year-olds), nearly half said they spend less to save more. The explanation is less common as age increases. One-third of 30- to 49-year-olds, 18 percent of 50- to 64-year-olds and 12 percent of those 65 and older say they spend less because they need to save. Most seniors aren’t saving enough for retirement, a separate study by found last week.

On the other hand, the concern over wages seems to grow with age. Only 19 percent of 18- to 29-year-olds said they were concerned about the lack of growth in their income, compared with 28 percent of 30- to 49-year-olds and 33 percent of 50- to 64-year-olds. Half of seniors, those 65 and older, said they can’t spend more because their income hasn’t changed.

Seniors are also the most likely to say they worry about the economy, but Americans’ overall concern about the economy has decreased this year.

“Worries about the economy have dissipated somewhat over the past year while consumers’ desire to forego additional spending in order to save more has increased,” McBride said.

Princeton Survey Research Associates International conducted’s survey and included answers from 1,007 adults in the continental U.S.