The overwhelming majority of 401(k) account holders are not contributing enough of their income to retire by age 65, according to a new report.

Nyhart, an independent actuarial and employee benefits consulting firms, based that conclusion on a six-month study of nearly 10,000 retirement accounts held by employees at 110 private and public companies.

The data showed that the amount employees were contributing out of their paychecks was exerting the biggest drag on their ability to save enough for retirement, according to Nyhart.

"The decision of how much employees contribute to their 401(k) far exceeds the importance of which investment funds they choose," said Thomas Totten, senior actuary and lead researcher for the study. "By increasing your contribution by just 2% to 4% of total income, you can shave years off the age you retire."

Among the study's findings:

    Eighty-one percent of employees 18 or older will not be able to afford to retire by the age of 65.
    Employees above the age of 55 will need to contribute more than 45% of pay through the remainder of their career to retire by age 65. Employees age 45-55 must contribute 19% of pay to retire by 65.
    The average participant, relying on their 401(k) as a primary retirement vehicle, will not be able to retire until the age of 73.
    Most employees 60 to 64 years old will likely need to work until the age of 75 to be able to afford to retire at their current levels of contribution to their 401(k).
    Thirty percent of employees 24 and under do not participate in a 401(k) benefit.
    Seven in ten employees 24 and under are not expected to retire by age 65.