NEW YORK — Workers are saving more for retirement, and the youngest – not exactly known for squirreling money away – are boosting their savings rates faster than any other age group.

Millennials between the ages of 25 and 34 are saving a median of 7.5 percent of their pay for retirement, including whatever match they get from their jobs, according to a survey by Fidelity Investments of 4,650 households with at least $20,000 of annual income. That’s up from 5.8 percent two years ago, when the last survey was conducted, and it is the largest jump among all age groups.

That’s still not enough, but at least the trend is getting better. Financial advisers suggest socking away 15 percent of pay, and more if workers haven’t saved in their earlier years.

Younger workers had the most room for improvement, because they were saving such a pittance. Older workers were already saving more of their paychecks. Workers aged 35 to 50 are now socking away 8.2 percent of their income, up from 7.7 percent two years ago. The oldest workers, aged 51 to 69, are saving 9.7 percent, up from 8.1 percent.

Several reasons are behind the rise, said John Sweeney, executive vice president of retirement and investment strategies at Fidelity, including an improving job market and economy. The unemployment rate is at its lowest level since 2008, and workers are feeling more comfortable in their jobs and with their finances.

Some workers are also saving more without knowing it, because their 401(k) and other retirement plans are automatically enrolling them and increasing how much they contribute each year.

The survey was Fidelity’s attempt at measuring how prepared workers are for retirement. Fidelity looked at how much workers make, spend and save, as well as when they expect to retire, among other factors. It found that 45 percent are likely to afford at least their essential expenses in retirement, up from 38 percent two years ago.

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