The latest official figures show the median time spent waiting for a promotion in federal government jobs has grown by more than six months in the space of just one year.

A mid-ranking departmental official could expect to wait five-and-half years before taking their next step up the career ladder, according to the Australian Public Service Commission's 2013-2014 figures, up from 4.9 years the previous year.

Five years ago the median time spent on each classification was just 3.2 years.

The careers slowdown is also hitting the executive ranks, the figures reveal, with the median "length at level" for the senior executive service 5.5 years at June 2014, up from 5.0 years in 2013.

For junior and middle managers at executive level, it was 5.8 years, up from 5.2 years in 2013.

Five years ago the median length at level for SES and ELs was 3.6 years.

Public sector employment expert Linda Colley, from Central Queensland University, said she was not surprised by the figures with the job market, both within the service and in the broader economy, growing tighter.

"If you have a recruitment freeze or if you have a tight labour market and there's no jobs outside, then nobody is leaving the public service," Dr Colley said.

"The jobs aren't being created, people are afraid to retire because they don't know what their superannuation is doing."

"All those things mean there's no vacancies, which means there is a big queue of people internally waiting to move upwards who can't."

Dr Colley said a resulting lack of workers who were relatively new to the service was resulting in a stagnation of the workforce.

"The other thing that is shrinking is the number of people with less than five years' experience as the hiring freeze really kicks in," she said.

"With fewer and fewer of those people who are new to the service, you have less rejuvenation at that end, more stagnation at the other end.

"It doesn't sound like a healthy recipe for a happy workforce."