Here's how much Americans have saved for retirement

As a group, Americans have shockingly little saved for retirement.

Northwestern Mutual's 2018 Planning & Progress Study, which surveyed 2,003 adults, found that 21 percent of Americans have nothing saved at all for their golden years, and a third of Americans have less than $5,000. To put that into perspective, it means that 31 percent of U.S. adults could last only a few months on their savings if they had to retire tomorrow.

That's probably why an increasing number of Americans say they'll rely on Social Security payouts, according to Gallup, but many also fear it won't be a reliable source of retirement income. Only 24 percent of Northwestern Mutual respondents say it's 'extremely likely' that Social Security will be available when they retire. Unfortunately, it's true that, if Congress doesn't act to shore it up, Social Security could be insolvent by 2034.

The average amount Americans have socked away for the future is slightly higher, but it's still just $84,821 — far less than the $1 million typically recommended by experts to supplement Social Security, pensions and any other sources of funding you may have.

Young people who haven't had as much time to save aren't skewing the statistics, either. The report found that 33 percent of boomers have $25,000 or less in retirement savings.

Additionally, 78 percent of Americans say they're 'extremely' or 'somewhat' concerned about not having enough money for retirement and another 66 percent believe that they'll outlive their retirement savings.

For that reason, many people are forced to stay in the workforce longer. Over half of the survey respondents believe they'll have to continue to working past the typical retirement age out of necessity.

"Continuing to work later in life should be a personal choice, not a mandatory requirement for survival," says Rebekah Barsch, vice president of planning for Northwestern Mutual. "Proactive financial planning can be the difference between a desired and a default retirement lifestyle."

To ensure that you'll have enough to comfortably cover your expenses in retirement, it's crucial to start investing as early as you can. For most people, contributing to an employer-sponsored 401(k) plan is the simplest way to start saving for retirement. If your employer offers a match, you're essentially getting free money.

If your company doesn't offer a 401(k) plan, or even if it does, consider other helpful, tax-advantaged retirement funds such as a Roth IRA or traditional IRA. Read up on the different types of retirement accounts here.

Anyone looking to lower their expenses can consider downsizing their home, trimming their grocery bill or making it a priority to eliminate debt. And those with the capacity to take on additional work can bring in extra cash by renting out spare rooms, reselling items online or taking on freelance work. Here's how much the most common side hustles pay.

Don't miss: 67% of Americans say they'll outlive their retirement savings—here's how many have nothing saved at all

Like this story? Like CNBC Make It on Facebook!