Nearly half of middle-class Americans are not confident they'll be able to save enough for a comfortable retirement, according to a study done by Wells Fargo & Co. 

A total of 48 percent say they are not confident, and 34 percent say they will work until they are "at least 80" because they have not saved enough for retirement. The "at least 80" number is up from 25 percent in 2011 and 30 percent in 2012. 

The study of 1,000 interviews with middle-class Americans ages 25 to 75 found that 59 percent of respondents list their top day-to-day financial concern as "paying the monthly bills," an increase from 52 percent who gave that response in 2012. Only 13 percent called saving for retirement a priority. A total of 42 percent said saving and paying for bills is not possible. 

It appears that people who have a written plan for retirement are more confident. Of the 29 percent of respondents who said they had a written plan, 70 percent described themselves as confident about their future. Only 44 percent of those who do not have a plan were confident. 

Also of note: People in their 30s are saving a median of 6 percent of their income, 1 percentage point higher than people in their 20s and 40s. 

For more information on the survey, click here.