Participation in 401(k) plans, regardless of age or income, rises according to the size of a company, according to a report from the Employee Benefit Research Institute.

Size definitely matters, EBRI said. Workers at firms with fewer employees are significantly less likely to participate in a retirement plan than are workers at large firms. Participation in a retirement plan also is affected by the employer’s size, with participation increasing for full-time, full-year private-sector wage and salary workers ages 21 to 64 as firm size grows.

In companies with fewer than 10 employees, an average of 20.2% of workers contributed to their 401(k) or other retirement plan. In companies with 10 to 24 employees, 30.4% participated. In companies with 25 to 99 employees, the participation rate was 44.1%. If the company employed between 100 and 499, the rate jumped to 54.4%. For companies at the next stage, 500 to 999 employees, the contribution rate was 58.6%, and for the last category measured, companies with 1,000 or more employees, an average 66.4% of people contributed to the plan.

EBRI found that workers at small employers had a persistently lower level of participation across all age groups. Even among workers making $50,000 or more, a considerable disparity exists; 31% of people in this income bracket working for the smallest employers participated in a plan, compared with 88% of those working for employers with 1,000 or more employees.

Among all company sizes, 55% of full-time, full-year wage and salary workers age 21 to 64 participated in a retirement plan in 2008, virtually unchanged from the just over 55% who participated in 2007.

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