from US Census
The median number of years that wage and salary workers had been with their current employer was 4.6 years in January 2014, unchanged from January 2012.
Information on employee tenure has been obtained from supplemental questions in the Current Population Survey (CPS) every 2 years since 1996. These data are collected as part of the Displaced Worker Supplement, which is sponsored by the Employment and Training Administration of the U.S. Department of Labor. The CPS is a monthly sample survey of about 60,000 households that provides information on the labor force status of the civilian noninstitutional population age 16 and over. The questions about employee tenure measure how long workers had been with their current employer at the time of the survey. A number of factors can affect median tenure of workers, including changes in the age profile among workers, as well as changes in the number of hires and separations. For further information about the CPS, see the Technical Note.
Demographic Characteristics
In January 2014, median employee tenure (the point at which half of all workers had more tenure and half had less tenure) for men was 4.7 years, unchanged from January 2012. For women, median tenure in January 2014 was 4.5 years, about unchanged from January 2012. Among men, 30 percent of wage and salary workers had 10 years or more of tenure with their current employer, compared with 28 percent for women.
Median employee tenure was generally higher among older workers than younger ones. For example, the median tenure of workers ages 55 to 64 (10.4 years) was more than three times that of workers ages 25 to 34 years (3.0 years). A larger proportion of older workers than younger workers had 10 years or more of tenure. Among workers ages 60 to 64, 58 percent were employed for at least 10 years with their current employer in January 2014, compared with only 12 percent of those ages 30 to 34.
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Source: http://www.bls.gov/news.release/pdf/tenure.pdf